# TinkerPop Upgrade Information

This document helps users of Apache TinkerPop™ to understand the changes that come with each software release. It outlines new features, how to resolve breaking changes and other information specific to a release. This document is useful to end-users who are building applications on TinkerPop, but it is equally useful to TinkerPop providers, who build libraries and other systems on the core APIs and protocols that TinkerPop exposes.

These providers include:

- Graph System Provider

  - Graph Database Provider

  - Graph Processor Provider

- Graph Driver Provider * Graph Language Provider

- Graph Plugin Provider

# TinkerPop 3.5.0

The Sleeping Gremlin: No. 18 Entr’acte Symphonique

## TinkerPop 3.5.1

Release Date: July 19, 2021

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### tx() in Javascript

Javascript is now the first non-JVM variant of Gremlin to get support for remote transactions. An example of the `tx()` syntax can be found in the Javascript Transaction Section.

See: TINKERPOP-2557

## TinkerPop 3.5.0

Release Date: May 3, 2021

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Host Language Runtimes

TinkerPop implements Gremlin in a variety of different programming languages. For 3.5.0, there are a number of major upgrades to those programming language environments:

- Java - TinkerPop now builds and is compatible with Java 11.

- Python - Support for Python 2.x has been dropped completely. Users must use Python 3 going forward. For the most part, from a user’s perspective, there are no specific API changes to consider as a result of this change.

- Javascript - Upgraded to support Node version 10.

- Jython - Support for Jython has been removed and gremlin-python no longer produces a JVM-based artifact. This change means that the `GremlinJythonScriptEngine` no longer exists and there is no way to write native Python lambdas that can execute in Gremlin Server. All lambdas should be written using gremlin-groovy if they are needed.

- .NET - Gremlin.NET no longer targets .NET Standard 1.3, but only .NET Standard 2.0. Since .NET Core 2.0 and .NET Framework 4.6.1 already support this .NET Standard version, most users should not be impacted by this.

See: TINKERPOP-2076, TINKERPOP-2317, TINKERPOP-2335

#### Gremlint

Gremlint, the JavaScript library powering gremlint.com, is now part of the TinkerPop project. It provides utilities for formatting Gremlin queries, taking parameters such as indentation, maximum line length and dot placement into account.

Until recently Gremlint has been an independent project maintained by Øyvind Sæbø, a developer at Ardoq. Ardoq has since donated Gremlint, as well as gremlint.com, to TinkerPop so that it can serve as TinkerPop’s canonical Gremlin code formatter.

See: TINKERPOP-2530

#### Translators

`Translator` implementations were moved from a mostly quiet and internal feature of TinkerPop to a documented and more readily accessible form in 3.4.9. For 3.5.0, the functionality has been expanded significantly in a number of ways. First, for Java, `gremlin-core` now has a `JavascriptTranslator` and a `DotNetTranslator` which completes the set of Gremlin translation functions for the programming languages that TinkerPop supports. It is therefore now possible to convert Gremlin bytecode to string representations that can compile in C#, Groovy, Javascript and Python.

The following example demonstrates what this functionality looks like in Javascript but it is quite similar for each `Translator` implementation:

    // gremlin-core module
    import org.apache.tinkerpop.gremlin.process.traversal.translator.JavascriptTranslator;

    GraphTraversalSource g = ...;
    Traversal<Vertex,Integer> t = g.V().has("person","name","marko").
                                    where(in("knows")).
                                    values("age").
                                    map(Lambda.function("it.get() + 1"));

    Translator.ScriptTranslator javascriptTranslator = JavascriptTranslator.of("g");
    System.out.println(javascriptTranslator.translate(t).getScript());
    // OUTPUT: g.V().has("person","name","marko").where(__.in_("knows")).values("age").map(() => "it.get() + 1")

In addition, a native Python `Translator` implementation has been added that will generate a string of Gremlin that will compile on the JVM.

    from gremlin_python.process.translator import *

    g = ...
    t = (g.V().has('person','name','marko').
              where(__.in_("knows")).
              values("age"))

    # Groovy
    translator = Translator().of('g');
    print(translator.translate(t.bytecode));
    # OUTPUT: g.V().has('person','name','marko').where(__.in('knows')).values('age')

See: TINKERPOP-2451, TINKERPOP-2452, TINKERPOP-2527

#### Versions and Dependencies

Apache Commons

There is a major breaking change in the use of `Configuration` objects. Prior to 3.5.0, `Configuration` objects were from the Apache Commons `commons-configuration` library, but in this version, they are of `commons-configuration2`. While this is a breaking change, the fix for most implementations will be quite simple and amounts to changing the import statements from:

    org.apache.commons.configuration.*

to

    org.apache.commons.configuration2.*

It is also worth noting that default list handling in configurations is treated differently. TinkerPop largely disabled the default list handling approach in `Configuration` 1.x, but if that functionality is still needed, it can be reclaimed by setting the `LegacyListDelimiterHandler` - details for doing taking this step and other relevant upgrade information can be found in the 2.x Upgrade Documentation.

Neo4j

There were two key changes to the `neo4j-gremlin` module:

- The underlying Neo4j version moved from the 3.2.x line to 3.4.x line. Please see the Neo4j Upgrade FAQ for more information as features and configuration options may have changed.

- Experimental support for multi/meta-properties in Neo4j which were previously deprecated have now been permanently removed.

Groovy Dependency in Java Driver

The `gremlin-driver` module made its dependency on Groovy `optional` as its only reason for inclusion was to support `JsonBuilder` serialization and this feature is little known and perhaps even less used. Read more about this change here in the Upgrade Documentation in the Serialization Section under the subsection title "GraphSON and JsonBuilder".

See: TINKERPOP-2185

#### Shaded Java Driver

The `gremlin-driver` has an additional packaging which may make it easier to upgrade for some users who may have extensive dependency chains.

    <dependency>
       <groupId>org.apache.tinkerpop</groupId>
       <artifactId>gremlin-driver</artifactId>
       <version>3.5.1</version>
       <classifier>shaded</classifier>
    </dependency>

The above dependency with the `shaded` classifier shades all the non-optional dependencies of `gremlin-driver` and includes `gremlin-core` and `tinkergraph-gremlin` in an unshaded form. The slf4j dependency was not included because shading it can cause problems with its operations.

See: TINKERPOP-2476

#### Serialization

Java and Gryo

Since the first release of TinkerPop 3.x, Gryo has been the default serialization format for Gremlin Server and Java Driver. It was also used as the default serialization format for Gremlin Console remote connectivity to Gremlin Server. As of this release, Gryo has been replaced as the default by GraphBinary. All packaged configuration files and programmatic defaults have been modified as such.

It is still possible to utilize Gryo as a message serialization format by modifying Gremlin Server configuration files to include the appropriate Gryo configurations. If using Gryo, do not use earlier versions of the driver and server with 3.5.0. Use a 3.5.0 client to connect to a 3.5.0 server. Generally speaking, mixed version combinations will appear to work properly, but problems will likely occur during general course of usage and it is therefore not advisable to take this approach.

For best compatibility between 3.4.x and 3.5.x, please use GraphBinary.

GraphSON and JsonBuilder

GraphSON serialization support for Groovy’s `JsonBuilder` has been present since the first version of GraphSON. That approach to returning results has never materialized as a standardized way to use Gremlin as originally envisioned. While support for this serialization form is still present, the dependency on Groovy in `gremlin-driver` has been changed to "optional", which means that users who wish to continue to return `JsonBuilder` results for some reason must explicitly include `groovy` and `groovy-json` dependencies in their applications. For Maven this would mean adding the following dependencies:

    <dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy</artifactId>
        <version>${groovy.version}</version>
        <classifier>indy</classifier>
    </dependency>
    <dependency>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-json</artifactId>
        <version>${groovy.version}</version>
        <classifier>indy</classifier>
        <exclusions>
            <!-- exclude non-indy type -->
            <exclusion>
                <groupId>org.codehaus.groovy</groupId>
                <artifactId>groovy</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

The `${groovy.version}` should match the version specified in TinkerPop’s root pom.xml.

.NET: GraphBinary

Gremlin.NET now also supports GraphBinary. GraphSON 3 however still remains the default serialization format as GraphBinary should be considered experimental for this version in .NET:

    var client = new GremlinClient(new GremlinServer("localhost", 8182), new GraphBinaryMessageSerializer());
    var g = Traversal().WithRemote(new DriverRemoteConnection(client));

.NET: New JSON Library

Gremlin.NET now uses `System.Text.Json` instead of Newtonsoft.Json as `System.Text.Json` is already included in .NET Core 3.0 and higher which removes a dependency and offers better performance. Most users should not notice this change, however users who have implemented their own GraphSON serializers or deserializers will need to modify them accordingly. The same applies to users that let Gremlin.NET return data without deserializing it first as the returned data types will change in this case, for example from Newtonsoft.Json’s `JObject` or `JToken` to `JsonElement` with `System.Text.Json`.

Python dict Deserialization

In Gremlin it is common to return a `dict` or `list` as a key value in another `dict`. The problem for Python is that these values are not hashable and will result in an error. By introducing a `HashableDict` and `Tuple` for those keys (respectively), it is now possible to return these types of results and not have to work around them:

    >>> g.V().has('person', 'name', 'marko').elementMap("name").groupCount().next()
    {{<T.id: 1>: 1, <T.label: 4>: 'person', 'name': 'marko'}: 1}

See: TINKERPOP-2259, TINKERPOP-2349, TINKERPOP-2395, TINKERPOP-2407, TINKERPOP-2460, TINKERPOP-2472, Custom JSON serialization with Gremlin.NET

#### Transaction Improvements

The TinkerPop Transaction API and its related features have not changed much since TinkerPop 3.x was initially released. Transactions that extend beyond the scope of a single traversal (or request) have remained a feature for embedded use cases and script execution (where supported) even in the face of the rise of remote graph use cases. With the varying contexts that exist for how and when transactions can be used, it has led to a fair bit of confusion.

For 3.5.0, TinkerPop introduces a change in approach to transactions that has the goal of unifying the API and features for all use cases, while addressing the more current state of the graph ecosystem which has shifted heavily toward remote communication and more diverse programming language ecosystems beyond the JVM.

Note | The old transaction API remains intact in 3.5.0, so this version should be backward compatible with the old model for embedded transactions.

The new model for using a transaction looks like this:

    g = traversal().withEmbedded(graph)
    // or
    g = traversal().withRemote(conn)

    tx = g.tx() // create a Transaction object
    gtx = tx.begin()  // spawn a GraphTraversalSource from the Transaction
    assert tx.isOpen() == true
    gtx.addV('person').iterate()
    gtx.addV('software').iterate()
    tx.commit() // alternatively you could explicitly rollback()
    assert tx.isOpen() == false

    // it is still possible to use g, but gtx is "done" after it is closed so use
    // tx.begin() to produce a new gtx instance for a fresh transaction
    assert 2 == g.V().count().next()

The first important point to take away here is that the same transaction code will work for either embedded or remote use cases. The second important point is that for remote cases, transaction support with bytecode is a wholly new feature, which was implemented by providing support for bytecode in sessions. Up until this time, sessions could only support script-based requests, so that makes another added feature related to this one.

Important | The `g.tx()` is only supported in Java at this time. Support for other languages will come available in future releases on the 3.5.x line.

See: TINKERPOP-2537, Reference Documentation - Transactions

#### Anonymous Child Traversals

TinkerPop conventions for child traversals is to spawn them anonymously from `__`, therefore:

    g.addV('person').addE('self').to(__.V(1))

or more succinctly via static import as:

    g.addV('person').addE('self').to(V(1))

Some users have chosen to instead write the above as:

    g.addV('person').addE('self').to(g.V(1))

which spawns a child traversal from a `GraphTraversalSource`. When spawned this way, a traversal is bound to a "source" and therefore is not anonymous. While the above code worked, it is important that there be less ways to do things with Gremlin so as to avoid confusion in examples, documentations and mailing list answers.

As of 3.5.0, attempting to use a traversal spawned from a "source" will result in an exception. Users will need to modify their code if they use the unconventional syntax.

See: TINKERPOP-2361

#### Use of null

Gremlin has traditionally disallowed `null` as a value in traversals and not always in consistent ways:

    gremlin> g.inject(1, null, null, 2, null)
    java.lang.NullPointerException
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n
    gremlin> g.V().has('person','name','marko').property('age', null)
    The AddPropertyStep does not have a provided value: AddPropertyStep({key=[age]})
    Type ':help' or ':h' for help.
    Display stack trace? [yN]
    gremlin> g.addV("person").property("name", 'stephen').property("age", null)
    ==>v[13]
    gremlin> g.V().has('person','name','stephen').elementMap()
    ==>[id:13,label:person,name:stephen]
    gremlin> g.V().constant(null)
    gremlin>

Note how `null` can produce exception behavior or act as a filter. For 3.5.0, TinkerPop has not only made `null` usage consistent, but has also made it an allowable value within a `Traversal`:

    gremlin> g.inject(1, null, null, 2, null)
    ==>1
    ==>null
    ==>null
    ==>null
    ==>2
    gremlin> g.V().constant(null)
    ==>null
    ==>null
    ==>null
    ==>null
    ==>null
    ==>null

TinkerGraph can be configured to support `null` as a property value and all graphs may not support this feature (for example, Neo4j does not). Please be sure to check the new `supportsNullPropertyValues()` feature (or the documentation of the graph provider) to determine if the `Graph` implementation allows `null` as a property value.

With respect to `null` in relation to properties, there was a bit of inconsistency in the handling of `null` in calls to `property()` depending on the type of mutation being executed demonstrated as follows in earlier versions:

    gremlin> g.V(1).property("x", 1).property("y", null).property("z", 2)
    The AddPropertyStep does not have a provided value: AddPropertyStep({key=[y]})
    Type ':help' or ':h' for help.
    Display stack trace? [yN]N
    gremlin> g.addV("test").property("x", 1).property("y", null).property("z", 2)
    ==>v[13]
    gremlin> g.V(13).properties()
    ==>vp[x->1]
    ==>vp[z->2]

This behavior has been altered to become consistent. First, assuming `null` is not supported as a property value, the setting of a property to `null` should have the behavior of removing the property in the same way in which you might do `g.V().properties().drop()`:

    gremlin> g.V(1).property("x", 1).property("y", null).property("z", 2)
    ==>v[1]
    gremlin> g.V(1).elementMap()
    ==>[id:1,label:person,name:marko,x:1,z:2,age:29]
    gremlin> g.V().hasLabel('person').property('age',null).iterate()
    gremlin> g.V().hasLabel('person').elementMap()
    ==>[id:1,label:person,name:marko]
    ==>[id:2,label:person,name:vadas]
    ==>[id:4,label:person,name:josh]
    ==>[id:6,label:person,name:peter]

Then, assuming `null` is supported as a property value, it would simply store the `null` for the key:

    gremlin> g.addV("person").property("name", 'stephen').property("age", null)
    ==>v[13]
    gremlin> g.V().has('person','name','stephen').elementMap()
    ==>[id:13,label:person,name:stephen,age:null]
    gremlin> g.V().has('person','age',null)
    ==>v[13]

The above described changes also have an effect on steps like `group()` and `groupCount()` which formerly produced exceptions when keys could not be found:

    gremlin> g.V().group().by('age')
    The property does not exist as the key has no associated value for the provided element: v[3]:age
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n

For situations where the key did not exist, the approach was to filter away vertices that did not have the available key so that such steps would work properly or to write a more complex `by()` modulator to better handle the possibility of a missing key. With the latest changes however none of that is necessary unless desired:

    gremlin> g.V().groupCount().by('age')
    ==>[null:2,32:1,35:1,27:1,29:1]

In conclusion, this improved support of `null` may affect the behavior of existing traversals written in past versions of TinkerPop as it is no longer possible to rely on `null` to expect a filtering action for traversers. Please review existing Gremlin carefully to ensure that there are no unintended consequences of this change and that there are no opportunities to improve existing logic to take greater advantage of this expansion of `null` semantics.

See: TINKERPOP-2235, TINKERPOP-2099

#### ByModulatorOptimizationStrategy

The new `ByModulatorOptimizationStrategy` attempts to re-write `by()` modulator traversals to use their more optimized forms which can provide a major performance improvement. As a simple an example, a traversal like `by(id())` would be replaced by `by(id)`, thus replacing a step-based traversal with a token-based traversal.

See: TINKERPOP-1682

#### SeedStrategy

The new `SeedStrategy` allows the user to set a seed value for steps that make use of `Random` so that the traversal has the ability to return deterministic results. While this feature is useful for testing and debugging purposes, there are also some practical applications as well.

    gremlin> g.V().values('name').fold().order(local).by(shuffle)
    ==>[josh,marko,vadas,peter,ripple,lop]
    gremlin> g.V().values('name').fold().order(local).by(shuffle)
    ==>[vadas,lop,marko,peter,josh,ripple]
    gremlin> g.V().values('name').fold().order(local).by(shuffle)
    ==>[peter,ripple,josh,lop,marko,vadas]
    gremlin> g.withStrategies(new SeedStrategy(22323)).V().values('name').fold().order(local).by(shuffle)
    ==>[lop,peter,josh,marko,vadas,ripple]
    gremlin> g.withStrategies(new SeedStrategy(22323)).V().values('name').fold().order(local).by(shuffle)
    ==>[lop,peter,josh,marko,vadas,ripple]
    gremlin> g.withStrategies(new SeedStrategy(22323)).V().values('name').fold().order(local).by(shuffle)
    ==>[lop,peter,josh,marko,vadas,ripple]

See: TINKERPOP-2014

#### by(T) for Property

The `Property` interface is not included in the hierarchy of `Element`. This means that an edge property or a meta-property are not considered elements the way that a `VertexProperty` is. As a result, some usages of `T` in relation to properties do not work consistently. One such example is `by(T)`, a token-based traversal, where the following works for a `VertexProperty` but will not for edge properties or meta-properties:

    gremlin> g.V(1).properties().as('a').select('a').by(key)
    ==>name
    ==>age

For a `Property` you would need to use `key()`-step:

    gremlin> g.E(11).properties().as('a').select(last,'a').by(key())
    ==>weight

Aside from the inconsistency, this issue also presents a situation where performance is impacted as token-based traversals are inherently faster than step-based ones. In 3.5.0, this issue has been resolved in conjunction with the introduction of `ByModulatorOptimizationStrategy` which will optimize `by(key())` and `by(value())` to their appropriate token versions automatically.

See: TINKERPOP-1682

#### match() Consistency

The `match()` step behavior might have seemed inconsistent those first using it. While there are a number of examples that might demonstrate this issue, the easiest one to consume would be:

    gremlin> g.V().match(__.as("a").out("knows").as("b"))
    ==>[a:v[1],b:v[2]]
    ==>[a:v[1],b:v[4]]
    gremlin> g.V().match(__.as("a").out("knows").as("b")).unfold()
    gremlin> g.V().match(__.as("a").out("knows").as("b")).identity()
    ==>[]
    ==>[]

The output is unexpected if there isn’t awareness of some underlying optimizations at play, where `match()` as the final step in the traversal implies that the user wants all of the labels as part of the output. With the addition of the extra steps, `unfold()` and `identity()` in the above case, the implication is that the traversal must be explicit in the labels to preserve from match, thus:

    gremlin> g.V().match(__.as("a").out("knows").as("b")).select('a','b').unfold()
    ==>a=v[1]
    ==>b=v[2]
    ==>a=v[1]
    ==>b=v[4]
    gremlin> g.V().match(__.as("a").out("knows").as("b")).select('a','b').identity()
    ==>[a:v[1],b:v[2]]
    ==>[a:v[1],b:v[4]]

Being explicit, as is the preference in writing Gremlin to good form, helps restrict the path history required to execute the traversal and therefore preserves memory. Of course, making `match()` a special form of end step is a confusing approach as the behavior of the step changes simply because another step is in play. Furthermore, correct execution of the traversal, relies on the execution of traversal strategies when the same traversal should produce the same results irrespective of the strategies applied to it.

In 3.5.0, we look to better adhere to that guiding design principle and ensure a more consistent output for these types of traversals. While the preferred method is to specify the labels to preserve from `match()` with a following `select()` step as shown above, `match()` will now consistently return all labels when they are not specified explicitly.

    gremlin> g.V().match(__.as("a").out("knows").as("b"))
    ==>[a:v[1],b:v[2]]
    ==>[a:v[1],b:v[4]]
    gremlin> g.V().match(__.as("a").out("knows").as("b")).identity()
    ==>[a:v[1],b:v[2]]
    ==>[a:v[1],b:v[4]]
    gremlin> g.V().match(__.as("a").out("knows").as("b")).unfold()
    ==>a=v[1]
    ==>b=v[2]
    ==>a=v[1]
    ==>b=v[4]

See: TINKERPOP-2481, TINKERPOP-2499

#### Gremlin Server

Remote SideEffects

Remote traversals no longer support the retrieval of remote side-effects. Users must therefore directly return side-effects as part of their query if they need that data. Note that server settings for `TraversalOpProcessor`, which formerly held the cache for these side-effects, no longer have any effect and can be removed.

Audit Logging

The `authentication.enableAuditlog` configuration property is deprecated and replaced by the `enableAuditLog` property to also make it available to `Authorizer` implementations. With the new setting enabled, there are slight changes in the formatting of audit log messages. In particular, the name of the authenticated user is included in every message.

Authorization

While Gremlin Server has long had authentication options to determine if a user can connect to the server, it now also contains the ability to apply a level of authorization to better control what a particular authenticated user will have access to. Authorization is controlled by the new `Authorizer` interface, which can be implemented by users and graph providers to provide this custom functionality.

UnifiedChannelizer

Gremlin Server uses a `Channelizer` abstraction to configure different Netty pipelines which can then offer different server behaviors. Most commonly, users configure the `WebSocketChannelizer` to enable the websocket protocol to which the various language drivers can connect.

TinkerPop 3.5.0 introduces a new `Channelizer` implementation called the `UnifiedChannelizer`. This channelizer is somewhat similar to the `WsAndHttpChannelizer` in that combines websocket and standard HTTP protocols in the server, but it provides a new and improved thread management approach as well as a more streamlined execution model. The `UnifiedChannelizer` technically replaces all existing implementations, but is not yet configured by default in Gremlin Server. To use it, modify the `channelizer` setting in the server yaml file as follows:

    channelizer: org.apache.tinkerpop.gremlin.server.channel.UnifiedChannelizer

As the `UnifiedChannelizer` is tested further, it will eventually become the default implementation. It may however be the preferred channelizer when using large numbers of short-lived sessions as the the threading model of the `UnifiedChannelizer` is better suited for such situations. If using this new channelizer, there are a few considerations to keep in mind:

- The `UnifiedChannelizer` does not use the `OpProcessor` infrastructure, therefore those configurations are no longer relevant and can be ignored.

- It is important to read about the `gremlinPool` setting in the Tuning Section of the reference documentation and to look into the new configurations available related to this channelizer: `maxParameters`, `sessionLifeTimeout`, `useGlobalFunctionCacheForSessions`, and `useCommonEngineForSessions`.

- Generally speaking, if current usage patterns involve mixing heavy loads of sessionless requests with arbitrary numbers of long-run sessions that have unpredictable end times, then the `UnifiedChannelizer` may not be the right choice for that situation. The long-run sessions will consume threads that would normally be available to sessionless requests and eventually slow their processing. On the other hand, if usage patterns involve mixing heavy loads of sessionless requests with short-lived sessions of similar execution time or if usage patterns allow the ability to predict the size of the pool that will support the workload then the `UnifiedChannelizer` will greatly improve performance over the old model.

See: TINKERPOP-2245, TINKERPOP-2269, TINKERPOP-2389, Reference Documentation

#### Retry Conditions

Some error conditions are temporary in nature and therefore an operation that ends in such a situation may be tried again as-is to potential success. In embedded use cases, an exception that implements the `TemporaryException` interface implies that the failing operation can be retried. For remote use cases, a `ResponseStatusCode` of `596` which equates to `SERVER_ERROR_TEMPORARY` is an indicator that a request may be retried.

With this more concrete and generalized approach to determining when retries should happen, the need to trap provider specific exceptions or to examine the text of error messages are removed. Before replacing existing code that might do these things currently, it may be best to include this sort of retry checking in addition to current methods as it may take time for providers to support these new options. Alternatively, if you can confirm that a provider does support this functionality then feel free to proceed wholly with this generalized TinkerPop approach.

Finally, it is important to note that TinkerPop drivers do not automatically retry when these conditions are met. It is up to the application to determine if retry is desired and how best to do so.

See: TINKERPOP-2517

#### Python Transport Layer

With the removal of Python 2.x support the transport layer of gremlin-python has been rewritten to use a library that utilizes the asyncio event loop of Python 3. AIOHTTP utilizes Python 3’s event loop with a minimal HTTP abstraction and is now used for the transport layer. From a user’s perspective there is not much of a change except there is now new configuration options available through named parameters, see AIOHTTP ws_connect for more details. This change fixed a number of issues that were related to the IOLoop of the old Tornado transport layer, which has been completely removed from the library. An additional config which enables the driver to be used from within an event loop has been added and can be used by setting `call_from_event_loop=True` when connecting.

See: TINKERPOP-1886, TINKERPOP-2388, TINKERPOP-2484, TINKERPOP-2546,

#### Python Kerberos Support

The Python Driver now supports Kerberos based authentication:

    g = traversal().withRemote(DriverRemoteConnection(
        'ws://localhost:8182/gremlin', 'g', kerberized_service='gremlin@hostname.your.org'))

See: TINKERPOP-1641, Reference Documentation

#### Deprecation Removal

The following deprecated classes, methods or fields have been removed in this version:

- `gremlin-core`

  - `org.apache.tinkerpop.gremlin.process.computer.bulkdumping.BulkDumperVertexProgram`

  - `org.apache.tinkerpop.gremlin.process.computer.bulkloading.BulkLoader`

  - `org.apache.tinkerpop.gremlin.process.computer.bulkloading.BulkLoaderVertexProgram`

  - `org.apache.tinkerpop.gremlin.process.computer.bulkloading.IncrementalBulkLoader`

  - `org.apache.tinkerpop.gremlin.process.computer.bulkloading.OneTimeBulkLoader`

  - `org.apache.tinkerpop.gremlin.process.computer.clustering.peerpressure.PeerPressureVertexProgram.Builder#traversal(*)`

  - `org.apache.tinkerpop.gremlin.process.computer.ranking.pagerank.PageRankVertexProgram.Builder#traversal(*)`

  - `org.apache.tinkerpop.gremlin.process.computer.ranking.pagerank.PageRankVertexProgram.Builder#vertexCount()`

  - `org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.PageRankVertexProgramStep.modulateBy(*)`

  - `org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.PageRankVertexProgramStep.modulateTimes()`

  - `org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.PeerPressureVertexProgramStep.modulateBy(*)`

  - `org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.PeerPressureVertexProgramStep.modulateTimes()`

  - `org.apache.tinkerpop.gremlin.process.remote.traversal.AbstractRemoteTraversalSideEffects`

  - `org.apache.tinkerpop.gremlin.process.remote.traversal.EmbeddedRemoteTraversalSideEffects`

  - `org.apache.tinkerpop.gremlin.process.remote.traversal.RemoteTraversalSideEffects`

  - `org.apache.tinkerpop.gremlin.process.remote.traversal.RemoteTraversal#getSideEffects()`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.decr`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.incr`

  - `org.apache.tinkerpop.gremlin.process.traversal.TraversalSource#withRemote(*)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversalSource#withRemote(*)`

  - `org.apache.tinkerpop.gremlin.process.traversal.step.map.PropertyMapStep(Traversal.Admin, boolean, PropertyType, String…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.step.map.PropertyMapStep#isIncludeTokens()`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.BytecodeUtil`

  - `org.apache.tinkerpop.gremlin.structure.util.star.StarGraph#builder()`

  - `org.apache.tinkerpop.gremlin.structure.util.star.StarGraph.Builder#create()`

- `gremlin-driver`

  - `org.apache.tinkerpop.gremlin.driver.Tokens#ARGS_SCRIPT_EVAL_TIMEOUT`

  - `org.apache.tinkerpop.gremlin.driver.Channelizer#createKeepAliveMessage()`

  - `org.apache.tinkerpop.gremlin.driver.Channelizer#supportsKeepAlive()`

  - `org.apache.tinkerpop.gremlin.driver.Cluster.Builder#keyCertChainFile(String)`

  - `org.apache.tinkerpop.gremlin.driver.Cluster.Builder#keyFile(String)`

  - `org.apache.tinkerpop.gremlin.driver.Cluster.Builder#keyPassword(String)`

  - `org.apache.tinkerpop.gremlin.driver.Cluster.Builder#maxWaitForSessionClose(Integer)`

  - `org.apache.tinkerpop.gremlin.driver.Cluster.Builder#trustCertificateChainFile(String)`

  - `org.apache.tinkerpop.gremlin.driver.handler.NioGremlinRequestEncoder`

  - `org.apache.tinkerpop.gremlin.driver.handler.NioGremlinResponseDecoder`

  - `org.apache.tinkerpop.gremlin.driver.remote.DriverRemoteTraversalSideEffects`

  - `org.apache.tinkerpop.gremlin.driver.remote.DriverRemoteTraversal#getSideEffects()`

  - `org.apache.tinkerpop.gremlin.driver.simple.NioClient`

- `gremlin-python`

  - `org.apache.tinkerpop.gremlin.python.jsr223.*`

- `gremlin-server`

  - `org.apache.tinkerpop.gremlin.server.Settings.scriptEvaluationTimeout`

  - `org.apache.tinkerpop.gremlin.server.Settings.SslSettings.keyCertChainFile`

  - `org.apache.tinkerpop.gremlin.server.Settings.SslSettings.keyFile`

  - `org.apache.tinkerpop.gremlin.server.Settings.SslSettings.keyPassword`

  - `org.apache.tinkerpop.gremlin.server.Settings.SslSettings.trustCertificateChainFile`

  - `org.apache.tinkerpop.gremlin.server.ResponseHandlerContext`

  - `org.apache.tinkerpop.gremlin.server.channel.NioChannelizer`

  - `org.apache.tinkerpop.gremlin.server.handler.NioGremlinBinaryRequestDecoder`

  - `org.apache.tinkerpop.gremlin.server.handler.NioGremlinResponseFrameEncoder`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractEvalOpProcessor.evalOpInternal(ResponseHandlerContext, Supplier, BindingSupplier)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.generateMetaData(ChannelHandlerContext, RequestMessage, ResponseStatusCode, Iterator)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.handleIterator(ResponseHandlerContext, Iterator)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.makeFrame(ChannelHandlerContext, RequestMessage, MessageSerializer, boolean, List, ResponseStatusCode, Map)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.makeFrame(Context, RequestMessage, MessageSerializer, boolean, List, ResponseStatusCode, Map)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.makeFrame(ResponseHandlerContext, RequestMessage, MessageSerializer, boolean, List, ResponseStatusCode, Map)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor.makeFrame(ResponseHandlerContext, RequestMessage, MessageSerializer, boolean, List, ResponseStatusCode, Map, Map)`

  - `org.apache.tinkerpop.gremlin.server.op.traversal.TraversalOpProcessor.onSideEffectSuccess(Graph, Context)`

  - `org.apache.tinkerpop.gremlin.server.util.SideEffectIterator`

- `neo4j-gremlin`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.Neo4jGraph#getTrait()`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.Neo4jGraph#CONFIG_META_PROPERTIES`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.Neo4jGraph#CONFIG_MULTI_PROPERTIES`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.trait.MultiMetaNeo4jTrait`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.trait.NoMultiNoMetaNeo4jTrait`

  - `org.apache.tinkerpop.gremlin.neo4j.structure.trait.Neo4jTrait`

Certain elements of the API were not or could not be deprecated in prior versions and were simply renamed for this release:

- `org.apache.tinkerpop.gremlin.driver.message.ResponseStatusCode#SERVER_ERROR_SCRIPT_EVALUATION` became `SERVER_ERROR_EVALUATION`

See: TINKERPOP-2080, TINKERPOP-2231, TINKERPOP-2233, TINKERPOP-2239, TINKERPOP-2269, TINKERPOP-2273, TINKERPOP-2455, 3.2.10 Upgrade Documentation for SSL

### Upgrading for Providers

#### Graph System Providers

##### Server Authorization

Gremlin Server now supports an extension model that enables authorization. Graph providers are not required to implement this functionality in any way, but it can be helpful for those graphs that wish to provide this functionality through Gremlin Server. Graphs Systems may still choose to rely on their own native authorization functionality if they so choose.

See: TINKERPOP-2389, Reference Documentation, Provider Documentation

##### ScalarMapStep

Previous versions of `MapStep` had a single abstract method that needed to be implemented:

    protected abstract E map(final Traverser.Admin<S> traverser);

This method made it easy to implement new implementations because it hid certain processing logic and made it so that the implementer only had to reason about how to take the current object from the `Traverser` and transform it to a new value. As 3.5.0 changed semantics around how `null` is processed, this method became a bit of a hindrance to the more complex logic which those semantics entailed. Specifically, this method could not easily communicate to underlying processing what a `null` might mean - is the `null` the end of the traversal stream or should the `null` be promoted down the stream as a value to be processed.

Interestingly, the method that enabled the handling of this more complex decision making already existed in `AbstractStep`:

    protected Traverser.Admin<E> processNextStart()

It returns a whole `Traverser` object and forces manual retrieval of the "next" `Traverser`. At this level it becomes possible to make choices on `null` and return it if it should be propagated or dismiss it and return an `EmptyTraverser`. To better accommodate the `MapStep` which provides the nice helper `map(Traverser)` method as well as the more flexible version that doesn’t need that infrastructure, `ScalarMapStep` was added to extend `MapStep`. The `map(Traverser)` was then moved to `ScalarMapStep` and those steps that could rely on that helper method now extend from it. All other steps of this sort still extend `MapStep` and directly implement `processNextStart()`.

Providers will get compile errors if they extended `MapStep`. The easy solution will be to simply modify that code so that their step instead extends `ScalarMapStep`. As a secondary task, providers should then examine their step implementation to ensure that `null` semantics as presented in 3.5.0 apply properly. If they do not, then it is likely that the step should simply implement `MapStep` directly and former `map(Traverser)` logic should be migrated to `processNextStart()`.

See: TINKERPOP-2235, TINKERPOP-2099

##### TraversalStrategy Application

The methodology for strategy application has been altered and the change is most easily described by example. Given a traversal with the structure:

    a(b(),c(d()))

Strategies were formerly applied in the following order:

    StrategyA on a
    StrategyB on a
    StrategyA on b
    StrategyB on b
    StrategyA on c
    StrategyB on c
    StrategyA on d
    StrategyB on d

This approach has always prevented strategies from performing global operations across the traversal and all decedents effectively as children will not have been processed by preceding strategies yet. As of this release, the approach has been altered to apply strategies as follows:

    StrategyA on a
    StrategyA on b
    StrategyA on c
    StrategyA on d
    StrategyB on a
    StrategyB on b
    StrategyB on c
    StrategyB on d

In this way, strategy B can check if it is being applied to the root traversal and if it is it knows that A has been applied globally.

This revised methodology could represent a breaking change for `TraversalStrategy` implementations if they somehow relied on the old ordering of application. It may also present an opportunity to revise how a `TraversalStrategy` is written to gain some processing benefit to the new order. Please be sure to review any custom strategies carefully when upgrading to this version.

As part of this change, there have been some adjustments to the `Traversal` and `Traversal.Admin` interfaces which have helped to clarify coding intent. There is now an `isRoot()` method which determines whether or not the traversal has a parent or not. Under revised semantics for 3.5.0, a traversal’s parent must be an `EmptyStep` instance and should not be `null`. With this change, provider `TraversalStrategy` implementations should be reviewed to evaluate if `isRoot()` semantics cause any breaks in logic to existing code.

In addition, `TraversalStrategies` now implements `Iterable` and exposes an `iterator()` method which may be preferred over the old `toList()` style construction for getting the list of configured strategies.

See: TINKERPOP-1568, TINKERPOP-2310, TINKERPOP-2311

##### Null Semantics

Graph providers should take note of the changes to `null` semantics described in the "users" section of these upgrade notes. As `null` is now acceptable as a `Traverser` object, this change may affect custom steps. Further note that `null` now works more consistently with mutation steps and graph providers may need to include additional logic to deal with those possible conditions. Please see the console sessions below which uses TinkerGraph to demonstrate the current behavioral expectations.

    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>false
    gremlin> g.addV(null).property(id, null).property('name',null)
    ==>v[0]
    gremlin> g.V().elementMap()
    ==>[id:0,label:vertex]
    ...
    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>true
    gremlin> g.addV(null).property(id, null).property('name',null)
    ==>v[0]
    gremlin> g.V().elementMap()
    ==>[id:0,label:vertex,name:null]

In the above example, `addV()` defaults to `Vertex.DEFAULT_LABEL`, the `id` is generated and setting the "name" property to `null` results in the value not being set. If the property value is set to an actual value and then set to `null` TinkerGraph will remove the property key all together:

    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>false
    gremlin> g.addV().property('name','stephen')
    ==>v[0]
    gremlin> g.V().elementMap()
    ==>[id:0,label:vertex,name:stephen]
    gremlin> g.V().has('vertex','name','stephen').property('name',null)
    ==>v[0]
    gremlin> g.V().elementMap()
    ==>[id:0,label:vertex]
    ...
    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>true
    gremlin> g.addV().property('name','stephen')
    ==>v[2]
    gremlin> g.V().has('vertex','name','stephen').property('name',null)
    ==>v[2]
    gremlin> g.V().elementMap()
    ==>[id:2,label:vertex,name:null]

The above examples point out the default operations of TinkerGraph, but it can be configured to actually accept the `null` as a property value and it is up to graph providers to decided how they wish to treat a `null` property value. Providers should use the new `supportsNullPropertyValues()` feature to indicate to users how `null` is handled.

For edges, the `label` still cannot be defaulted and must be specified, therefore:

    gremlin> g.V(0L).as('a').addE(null).to('a')
    Label can not be null
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n
    gremlin> g.V(0L).as('a').addE(constant(null)).to('a')
    Label can not be null
    Type ':help' or ':h' for help.
    Display stack trace? [yN]

Also, edges have similar behavior to vertices when it comes to setting properties (again, the default configuration for TinkerGraph is being used here):

    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>false
    gremlin> g.addV().property('name','stephen')
    ==>v[0]
    gremlin> g.V().has('vertex','name','stephen').as('a').addE('knows').to('a').property(id,null).property('weight',null)
    ==>e[2][0-knows->0]
    gremlin> g.E().elementMap()
    ==>[id:2,label:knows,IN:[id:0,label:vertex],OUT:[id:0,label:vertex]]
    gremlin> g.E().property('weight',0.5)
    ==>e[2][0-knows->0]
    gremlin> g.E().elementMap()
    ==>[id:2,label:knows,IN:[id:0,label:vertex],OUT:[id:0,label:vertex],weight:0.5]
    gremlin> g.E().property('weight',null)
    ==>e[2][0-knows->0]
    gremlin> g.E().elementMap()
    ==>[id:2,label:knows,IN:[id:0,label:vertex],OUT:[id:0,label:vertex]]
    ...
    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>true
    gremlin> g.addV().property('name','stephen')
    ==>v[8]
    gremlin> g.V().has('vertex','name','stephen').as('a').addE('knows').to('a').property(id,null).property('weight',null)
    ==>e[10][8-knows->8]
    gremlin> g.E().elementMap()
    ==>[id:10,label:knows,IN:[id:8,label:vertex],OUT:[id:8,label:vertex],weight:null]
    gremlin> g.E().property('weight',0.5)
    ==>e[10][8-knows->8]
    gremlin> g.E().elementMap()
    ==>[id:10,label:knows,IN:[id:8,label:vertex],OUT:[id:8,label:vertex],weight:0.5]
    gremlin> g.E().property('weight',null)
    ==>e[10][8-knows->8]
    gremlin> g.E().elementMap()
    ==>[id:10,label:knows,IN:[id:8,label:vertex],OUT:[id:8,label:vertex],weight:null]

Graphs that support multi/meta-properties have some issues to consider as well as demonstrated with TinkerGraph:

    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>false
    gremlin> g.addV().property(list,'foo',"x").property(list,"foo", null).property(list,'foo','bar')
    ==>v[0]
    gremlin> g.V().elementMap()
    ==>[id:0,label:vertex,foo:bar]
    gremlin> g.V().valueMap()
    ==>[foo:[x,bar]]
    gremlin> g.V().property('foo',null)
    ==>v[0]
    gremlin> g.V().valueMap(true)
    ==>[id:0,label:vertex]
    ...
    gremlin> g.addV().property(list,'foo','bar','x',1,'y',null)
    ==>v[0]
    gremlin> g.V().properties('foo').valueMap(true)
    ==>[id:1,key:foo,value:bar,x:1]
    gremlin> g.V().properties('foo').property('x',null)
    ==>vp[foo->bar]
    gremlin> g.V().properties('foo').valueMap(true)
    ==>[id:1,key:foo,value:bar]
    ...
    gremlin> g.getGraph().features().vertex().supportsNullPropertyValues()
    ==>false
    gremlin> g.addV().property(list,'foo',"x").property(list,"foo", null).property(list,'foo','bar')
    ==>v[11]
    gremlin> g.V().elementMap()
    ==>[id:11,label:vertex,foo:bar]
    gremlin> g.V().valueMap()
    ==>[foo:[x,null,bar]]
    ...
    gremlin> g.addV().property(list,'foo','bar','x',1,'y',null)
    ==>v[0]
    gremlin> g.V().properties('foo').valueMap(true)
    ==>[id:1,key:foo,value:bar,x:1,y:null]
    gremlin> g.V().properties('foo').property('x',null)
    ==>vp[foo->bar]
    gremlin> g.V().properties('foo').valueMap(true)
    ==>[id:1,key:foo,value:bar,x:null,y:null]

See: TINKERPOP-2235, TINKERPOP-2099

##### AbstractOpProcessor API Change

The `generateMetaData()` method was removed as it was deprecated in a previous version. There already was a preferred method called `generateResultMetaData()` that took an extra `Settings` parameter. To fix compilation issues simply replace implementations of the `generateMetaData()` method with `generateResultMetaData()`. Gremlin Server has only been calling `generateResultMetaData()` since the deprecation, so this correction should be straightforward.

##### StoreStep and AggregateStep

Note that `StoreStep` has been renamed to `AggregateLocalStep` and `AggregateStep` has been renamed to `AggregateGlobalStep`. The renaming is important to consider if any custom `TraversalStrategies` have been written that rely on the old step names.

See: TINKERPOP-2254

##### Session Close

TinkerPop drivers no longer send the session "close" message to kill a session. The close of the connection itself should be responsible for the close of the session. It is also expected that a session is bound to the client that created it. Closing the session explicitly by closing the connection will act as a force close where transaction are not explicitly rolled-back by Gremlin Server. Such transactions would be handled by the underlying graph system in the manner that they provide.

See: TINKERPOP-2336

##### TemporaryException and SERVER_ERROR_TEMPORARY

The `gremlin-core` module now has a `TemporaryException` interface. This interface allows providers to throw an exception that will be considered by users to be generally retryable. In addition, the Gremlin Server protocol now also has a `ResponseStatusCode.SERVER_ERROR_TEMPORARY` status which indicates the same situation. Throwing an exception that implements `TemporaryException` will be recognized by Gremlin Server to return this error code. This notion of "temporary failure" is helpful to providers as it allows them to let users know that a failure is transient and related to the system state at the time of the request. Without this indicator, users are left to parse exception messages to determine when it is considered acceptable to retry an operation.

See: TINKERPOP-2517

##### gremlin-language

The new `gremlin-language` module contains an ANTLR4 grammar for the Gremlin language along with the generated parser code. The grammar is still under development but covers most of the Gremlin language, with the idea that it will eventually drive the ongoing design of the language, as opposed to driving it from Java.

The grammar is currently tested against the Gremlin traversals in the entire Gherkin test suite, as well as a major portion of the Gremlin used for examples in the Reference Documentation. The grammar has the following limitations:

- It does not support lambdas or Groovy syntax

- The following steps are not yet fully supported:

  - `withComputer()`

  - `io()`

  - `withoutStrategies()`

  - `program()`

  - `connectedComponent()`

  - `fill()` terminator step

- `Vertex` and `Edge` instance definitions

See: TINKERPOP-2533

##### UnifiedChannelizer

The `UnifiedChannelizer` is a new `Channelizer` implementation. It exposes new a new `Session` interface that allows this channelizer to be extended with custom functionality specific to a providers environment. As of 3.5.0, this channelizer is not the default and only fits certain workload patterns. The interfaces should therefore be considered volatile and may change.

See: TINKERPOP-2245

#### Graph Driver Providers

##### TraversalOpProcessor Side-effects

`TraversalOpProcessor` no longer holds a cache of side-effects and more generally the entire side-effect protocol has been removed and is no longer supported in the server or drivers.

See: TINKERPOP-2269

##### Close Message

The functionality of the "close" message is no longer in place in Gremlin Server. Sending the message (from older drivers for example) will simply result in a no-op on the server and the expected return of the `NO_CONTENT` message. From 3.5.0 forward, drivers need not send this message to close the session and simply rely on the close of the connection to kill the session.

See: TINKERPOP-2336

# TinkerPop 3.4.0

Avant-Gremlin Construction #3 for Theremin and Flowers

## TinkerPop 3.4.12

Release Date: July 19, 2021

Please see the changelog for a complete list of all the modifications that are part of this release.

## TinkerPop 3.4.11

Release Date: May 3, 2021

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### barrier() Control

Various `TraversalStrategy` implementations inject `barrier()` instances to improve traversal performance. It is often helpful in debugging situations or in tweaking traversal performance activities that it may be necessary to prevent automated `barrier()` injection. Formerly, that involved removing `LazyBarrierStrategy`, `RepeatUnrollStrategy`, and `PathRetractionStrategy` as all three of those strategies had the potential to add a `barrier()`. While this approach would work, it may be hard to recall those three strategies easily and you may be removing optimizations that might have been useful in addition to the `barrier()`.

In 3.4.11, it is only necessary to remove `LazyBarrierStrategy`. Doing so will disable `barrier()` additions in other strategies and as this is the new model of execution, it can be expected to work as the approach in the future even if other strategies attempt to add `barrier()` steps for some reason. Note of course that this rule only applies to TinkerPop-enabled strategies. It is possible that provider-specific strategies could add `barrier()`-steps and thus still require direct removal.

    gremlin> g.V().repeat(out()).times(2).in().explain()
    ==>Traversal Explanation
    ====================================================================================================================================================================================
    Original Traversal                 [GraphStep(vertex,[]), RepeatStep([VertexStep(OUT,vertex), RepeatEndStep],until(loops(2)),emit(false)), VertexStep(IN,vertex)]

    ConnectiveStrategy           [D]   [GraphStep(vertex,[]), RepeatStep([VertexStep(OUT,vertex), RepeatEndStep],until(loops(2)),emit(false)), VertexStep(IN,vertex)]
    RepeatUnrollStrategy         [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    IncidentToAdjacentStrategy   [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    MatchPredicateStrategy       [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    PathRetractionStrategy       [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    FilterRankingStrategy        [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    InlineFilterStrategy         [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    AdjacentToIncidentStrategy   [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    CountStrategy                [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    EarlyLimitStrategy           [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    LazyBarrierStrategy          [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]
    TinkerGraphCountStrategy     [P]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]
    TinkerGraphStepStrategy      [P]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]
    ProfileStrategy              [F]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]
    StandardVerificationStrategy [V]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]

    Final Traversal                    [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(OUT,vertex), NoOpBarrierStep(2500), VertexStep(IN,vertex)]
    gremlin> g.withoutStrategies(LazyBarrierStrategy).V().repeat(out()).times(2).in().explain()
    ==>Traversal Explanation
    =================================================================================================================================================================
    Original Traversal                 [GraphStep(vertex,[]), RepeatStep([VertexStep(OUT,vertex), RepeatEndStep],until(loops(2)),emit(false)), VertexStep(IN,vertex)]

    ConnectiveStrategy           [D]   [GraphStep(vertex,[]), RepeatStep([VertexStep(OUT,vertex), RepeatEndStep],until(loops(2)),emit(false)), VertexStep(IN,vertex)]
    RepeatUnrollStrategy         [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    CountStrategy                [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    EarlyLimitStrategy           [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    MatchPredicateStrategy       [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    FilterRankingStrategy        [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    IncidentToAdjacentStrategy   [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    PathRetractionStrategy       [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    InlineFilterStrategy         [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    AdjacentToIncidentStrategy   [O]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    TinkerGraphCountStrategy     [P]   [GraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    TinkerGraphStepStrategy      [P]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    ProfileStrategy              [F]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]
    StandardVerificationStrategy [V]   [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]

    Final Traversal                    [TinkerGraphStep(vertex,[]), VertexStep(OUT,vertex), VertexStep(OUT,vertex), VertexStep(IN,vertex)]

See: TINKERPOP-1994

## TinkerPop 3.4.10

Release Date: January 18, 2021

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Python Timeout Issue

In version 3.4.9, it became possible to set client-side read/write timeouts. Those timeouts were defaulted to thirty seconds which could put the client at odds with other timeout settings which could then cause unexpected failures. The client-side timeouts have now been defaulted to `None` leaving it to users to set the timeout themselves if they so desire. In this way, 3.4.10 has the same timeout behavior as 3.4.8 without any additional workarounds.

The timeouts can be configured as shown in the below example:

    from gremlin_python.driver.tornado.transport import TornadoTransport

    graph=Graph()
    connection = DriverRemoteConnection(endpoint,'g',
                     transport_factory=lambda: TornadoTransport(read_timeout=60, write_timeout=60))

    g = graph.traversal().withRemote(connection)

See: TINKERPOP-2505

## TinkerPop 3.4.9

Release Date: December 7, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

Warning | Python users should prefer use of 3.4.10 to avoid an issue with a default timeout setting that requires direct configuration described in TINKERPOP-2505.

### Upgrading for Users

#### Translator Implementations

One of the silent features of Gremlin is the `ScriptTranslator`. More specifically, the implementation of this interface which will convert a `Traversal` object (or Gremlin `Bytecode`) into a proper `String` representation that is syntactically correct for the implementation language.

    gremlin> import org.apache.tinkerpop.gremlin.process.traversal.translator.*
    ==>org.apache.tinkerpop.gremlin.structure.*, org.apache.tinkerpop.gremlin.structure.util.*, ...
    gremlin> translator = GroovyTranslator.of('g')
    ==>translator[g:gremlin-groovy]
    gremlin> translator.translate(g.V().has("person","name","marko").has("age",gt(20)).where(outE("knows")))
    ==>g.V().has("person","name","marko").has("age",P.gt((int) 20)).where(__.outE("knows"))
    gremlin> translator = PythonTranslator.of('g')
    ==>translator[g:gremlin-python]
    gremlin> translator.translate(g.V().has("person","name","marko").has("age",gt(20)).where(outE("knows")))
    ==>g.V().has('person','name','marko').has('age',P.gt(20)).where(__.outE('knows'))

Some Gremlin users may already be aware of the implementations for Groovy and Python from previous versions. These classes have largely been used for testing purposes, but users have found helpful use cases for them and they have now been promoted to `gremlin-core` from their original locations. The old versions in `gremlin-groovy` and `gremlin-python` have been deprecated. There have been some improvements to the `GroovyTranslator` such that the Gremlin generated will not match character for character with the deprecated version. There may also be some potential for the newer version in 3.4.9 to generate scripts that will not work in earlier versions. It is therefore best to use 3.4.9 translators within environments where 3.4.9 is uniformly supported. If older versions are in place, it may be better to continue use of the deprecated versions.

See: TINKERPOP-2461

#### Bytecode Command Improvements

The `:bytecode` command in the Gremlin console includes two new options: `reset` and `config`. Both options provide ways to better control the `GraphSONMapper` used internally by the command. The `reset` option will replace the current `GraphSONMapper` with a new one with some basic defaults: GraphSON 3.0 with extension and `TinkerIoRegistry` if present. The `config` option provides a way to specify a custom `GraphSONMapper` or additional configurations to the default one previously described.

See: TINKERPOP-2479

#### withStrategies() Groovy Syntax

The `withStrategies()` configuration step accepts a variable number of `TraversalStrategy` instances. In Java, those instances are typically constructed with `instance()` if it is a singleton or by way of a builder pattern which provides a fluent, type safe method to create the object. For Groovy, which is highly applicable to those who use Gremlin scripts in their applications or work a lot within tools similar to the Gremlin Cosnole, the builder syntax can work but doesn’t really match the nature of the Groovy language. Using a strategy in this script context would look something like:

    g.withStrategies(ReadOnlyStrategy.instance(),
                     SubgraphStrategy.build().vertexProperties(hasNot('endTime')).create())

While this method will still work, it is now possible to use a more succinct syntax for Groovy scripts:

    g.withStrategies(ReadOnlyStrategy,
                     new SubgraphStrategy(vertexProperties: __.hasNot('endTime')))

The rules are straightforward. If a strategy can be instantiated with `instance()` as a singleton then use just the class name as a shortcut. Interestingly, many users try this syntax when they first get started and obviously fail. With the syntax present, they will have one less error to contend with in their early days of Gremlin. For strategies that take configurations, these strategies will use named arguments in the constructor where the names match the expected builder methods. This named argument syntax is common to Groovy and not something special to Gremlin - it is just now exposed for this purpose.

See: TINKERPOP-2466

#### withEmbedded()

The `AnonymousTraversalSource` was introduced in 3.3.5 and is most typically used for constructing remote `TraversalSource` instances, but it also provides a way to construct a `TraversalSource` from an embedded `Graph` instance:

    gremlin> g = traversal().withGraph(TinkerFactory.createModern())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g = traversal().withRemote(DriverRemoteConnection.using('localhost',8182))
    ==>graphtraversalsource[emptygraph[empty], standard]

The `withGraph(Graph)` method is now deprecated in favor the new `withEmbedded(Graph)` method that is more explicit about its intent:

    gremlin> g = traversal().withEmbedded(TinkerFactory.createModern())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]

This change is mostly applicable to JVM languages where embedded `Graph` instances are available. For Gremlin Language Variants not on the JVM, the `withGraph(Graph)` method has simply been deprecated and not replaced (with the preference to use `withRemote()` variants).

See: TINKERPOP-2413

#### TraversalStrategy in Javascript

Using `SubgraphStrategy`, `PartitionStrategy` and other `TraversalStrategy` implementations is now possible in Javascript.

    const sg = g.withStrategies(
              new SubgraphStrategy({vertices:__.hasLabel("person"), edges:__.hasLabel("created")}));

See: TINKERPOP-2054

#### WebSocket Compression

Gremlin Server now supports standard WebSocket compression (per RFC 7692). Both the Java and Python drivers support this functionality from the client’s perspective. Compression is enabled by default and should be backward compatible, thus allowing older versions of the driver to connect to newer versions of the server and vice versa. Using the compression-enabled drivers with a server that also supports that functionality will greatly reduce network IO requirements.

See: TINKERPOP-2441, TINKERPOP-2453

#### Connection Management Improvements

The Java Driver was designed with the idea that a `Cluster` instance would be created once and then used for the life of the application. As a result, the cost of setup and termination of that instance was typically sunk into the general startup and shutdown of the application itself. In some environments, where applications were short-lived, this cost was quite apparent and undesirable given that it might take several seconds to initialize and then a similar amount of time for proper shutdown.

In 3.4.9, the initialization and shutdown of the `Cluster` object has been improved dramatically, which should be especially helpful to those aforementioned ephemeral environments. The following micro-benchmark results demonstrate the difference in performance between 3.4.8 and 3.4.9:

Benchmark | 3.4.8 | 3.4.9
--- | --- | ---
setup and close 100 connections | 2116 ms | 35 ms
setup and close 32 connections | 2081 ms | 13 ms
setup and close 1 connection | 2046 ms | 2 ms

See: TINKERPOP-2445

#### Per Request Options

With Java it has been possible to pass per-request settings for both scripts and bytecode. While Javascript, Python, and .NET allowed this in various ways, it wasn’t quite as convenient as Java, nor was it well documented. In this release, the approach for making this sort of per-request configurations is now much more consistent across languages. We see this most evident in bytecode based requests:

Java

    g.with(Tokens.ARGS_EVAL_TIMEOUT, 500L).V().out("knows");

C#

    g.With(Tokens.ArgsEvalTimeout, 500).V().Out("knows").Count();

Javascript

    g.with_('evaluationTimeout', 500).V().out('knows');

Python

    g.with_('evaluationTimeout', 500).V().out('knows')

Please see the new "Per Request Settings" sections for each language in the Gremlin Drivers and Variants section for information on how to send scripts with specific request configurations.

See: TINKERPOP-2296, TINKERPOP-2420, TINKERPOP-2421

#### GraphManager Extension

The `org.apache.tinkerpop.gremlin.server.util.CheckedGraphManager` can be used instead of `org.apache.tinkerpop.gremlin.server.util.DefaultGraphManager` (in gremlin-server.yml to ensures that Gremlin Server fails to start if all graphs fails. This configuration option can be useful for a number of different situations (e.g. use `CheckedGraphManager` on a Kubernetes cluster to ensure that a pod will be restarted when it cannot properly handle requests.) As a final note, `DefaultGraphManager` is no longer `final` and thus can be extended.

See: TINKERPOP-2436

#### Lambdas in gremlin-javascript

Lambda scripts can now be utilized in `gremlin-javascript` and follows roughly the same pattern as Python does:

    g.V().has('person','name','marko').
      values('name').map(() => "it.get()[1]")

See: TINKERPOP-2001

### Upgrading for Providers

#### Graph System Providers

##### Custom TraverserSet

It is now possible to provide a custom `TraverserSet` to `Step` implementations that make use of those objects to introduce new logic for how they are populated and managed. Providers can take advantage of this capability by constructing their own `Traversal` implementation and overriding the `getTraverserSetSupplier()` method. When new `TraverserSet` instances are needed during traversal execution, steps will consult this method to get those instances.

See: TINKERPOP-2396

## TinkerPop 3.4.8

Release Date: August 3, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin.NET: Automatic Reconnect

The Gremlin.NET driver now automatically tries to reconnect to a server when no open connection is available to submit a request. This should enable the driver to handle cases where the server is only temporarily unavailable or where the server has closed connections which some graph providers do when no requests were sent for some time.

See: TINKERPOP-2288

## TinkerPop 3.4.7

Release Date: June 1, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Clear Screen Command

Gremlin Console now has the `:cls` command to clear the screen. This feature acts as an alternative to platform specific clear operations and provides a common way to perform that function.

TINKERPOP-2357

## TinkerPop 3.4.6

Release Date: February 20, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### drop() Properties

In 3.4.5 the equality of the `Property` object changed to allow language features like `dedup()` to work more consistently. An unnoticed side-effect of that change was that calling `drop()` on properties that had the same values would not properly remove all their instances. This problem affected edge and meta property instances but not the properties of vertices as their equality definitions had not changed.

This issue is now resolved with the side-effect being that the inclusion of `drop()` will disable `LazyBarrierStrategy` which prevents automatic bulking. In most common cases, the impact of that optimization loss should be minimal and could be added back manually with `barrier()` steps in the appropriate places.

See: TINKERPOP-2338

## TinkerPop 3.4.5

Release Date: February 3, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

Warning | A bug was noted in 3.4.5 soon after release and was quickly patched. Users and providers should avoid version 3.4.5 and should instead prefer usage of 3.4.6.

### Upgrading for Users

#### by(String) Modulator

It is quite common to use the `by(String)` modulator when doing some for of selection operation where the `String` is the key to the value of the current `Traverser`, demonstrated as follows:

    gremlin> g.V().project('name').by('name')
    ==>[name:marko]
    ==>[name:vadas]
    ==>[name:lop]
    ==>[name:josh]
    ==>[name:ripple]
    ==>[name:peter]
    gremlin> g.V().order().by('name').values('name')
    ==>josh
    ==>lop
    ==>marko
    ==>peter
    ==>ripple
    ==>vadas

Of course, this approach usually only works when the current `Traverser` is an `Element`. If it is not an element, the error is swift and severe:

    gremlin> g.V().valueMap().project('x').by('name')
    java.util.LinkedHashMap cannot be cast to org.apache.tinkerpop.gremlin.structure.Element
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n

and while it is perhaps straightforward to see the problem in the above example, it is not always clear exactly where the mistake is. The above example is the typical misuse of `by(String)` and comes when one tries to treat a `Map` the same way as an `Element` (which is quite reasonable).

In 3.4.5, the issue of using `by(String)` on a `Map` and the error messaging have been resolved as follows:

    gremlin> g.V().valueMap().project('x').by('name')
    ==>[x:[marko]]
    ==>[x:[vadas]]
    ==>[x:[lop]]
    ==>[x:[josh]]
    ==>[x:[ripple]]
    ==>[x:[peter]]
    gremlin> g.V().elementMap().order().by('name')
    ==>[id:4,label:person,name:josh,age:32]
    ==>[id:3,label:software,name:lop,lang:java]
    ==>[id:1,label:person,name:marko,age:29]
    ==>[id:6,label:person,name:peter,age:35]
    ==>[id:5,label:software,name:ripple,lang:java]
    ==>[id:2,label:person,name:vadas,age:27]
    gremlin> g.V().values('name').project('x').by('name')
    The by("name") modulator can only be applied to a traverser that is an Element or a Map - it is being applied to [marko] a String class instead
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n

See: TINKERPOP-2314

#### hasKey() Step and hasValue() Step

Previously, `hasKey()`-step and `hasValue()`-step only applied to vertex properties. In order to support more generalized scenarios, the behavior of these steps were modified to allow them to be applied to both edge properties and meta-properties.

The original behavior is demonstrated as follows:

    gremlin> graph = TinkerFactory.createTheCrew()
    ==>tinkergraph[vertices:6 edges:14]
    gremlin> g = graph.traversal()
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:14], standard]
    gremlin> g.E().properties().hasKey('since')
    ==>TinkerProperty cannot be cast to Element
    gremlin> g.V().properties("location").properties().hasKey("startTime")
    ==>TinkerProperty cannot be cast to Element
    gremlin> g.E().properties().hasValue(2010)
    ==>TinkerProperty cannot be cast to Element
    gremlin> g.V().properties("location").properties().hasValue(2005)
    ==>TinkerProperty cannot be cast to Element

The new behavior of `hasKey()` with edge property can be seen as:

    gremlin> g.E().properties().hasKey('since')
    ==>p[since->2009]
    ==>p[since->2010]
    ==>p[since->2010]
    ==>p[since->2011]
    ==>p[since->2012]

Similar behavior of for `hasKey()` can be seen with meta-properties:

    gremlin> g.V().properties().hasKey('location').properties().hasKey('startTime')
    ==>p[startTime->1997]
    ==>p[startTime->2001]
    ==>p[startTime->2004]
    ==>p[startTime->2004]
    ==>p[startTime->2005]
    ==>p[startTime->2005]
    ==>p[startTime->1990]
    ==>p[startTime->2000]
    ==>p[startTime->2006]
    ==>p[startTime->2007]
    ==>p[startTime->2011]
    ==>p[startTime->2014]
    ==>p[startTime->1982]
    ==>p[startTime->2009]

The new behavior for `hasValue()` with edge property is as follows:

    gremlin> g.E().properties().hasValue(2010)
    ==>p[since->2010]
    ==>p[since->2010]

and similarly with `hasValue()` for meta-properties:

    gremlin> g.V().properties().hasKey('location').properties().hasValue(2005)
    ==>p[endTime->2005]
    ==>p[endTime->2005]
    ==>p[startTime->2005]
    ==>p[startTime->2005]

TINKERPOP-1733

#### Properties Equality

There was some inconsistency in terms of `Property` equality in earlier versions of Gremlin. Equality is now defined as follows: two properties are equal only if their key and value are equal, even if their parent elements are not equal. It makes sense when comparing properties regardless of parent elements to just focus on the property itself as it yields more uniform and concise results to reason about. The benefit of this change is that the behavior of property comparison and `dedup()`-step are predictable, and it will not affect the result if the property is detached from the parent element.

Note | The "property" here refer to edge properties and meta-properties, thus excluding vertex property.

The old behavior can be shown using "The Crew" toy graph as follows:

    gremlin> g.E().properties().count()
    ==>13
    gremlin> g.E().properties()
    ==>p[since->2009]
    ==>p[since->2010]
    ==>p[skill->4]
    ==>p[skill->5]
    ==>p[since->2010]
    ==>p[since->2011]
    ==>p[skill->5]
    ==>p[skill->4]
    ==>p[since->2012]
    ==>p[skill->3]
    ==>p[skill->3]
    ==>p[skill->5]
    ==>p[skill->3]
    gremlin> g.E().properties().dedup().count()
    ==>13
    gremlin> g.E().dedup().properties()
    ==>p[since->2009]
    ==>p[since->2010]
    ==>p[skill->4]
    ==>p[skill->5]
    ==>p[since->2010]
    ==>p[since->2011]
    ==>p[skill->5]
    ==>p[skill->4]
    ==>p[since->2012]
    ==>p[skill->3]
    ==>p[skill->3]
    ==>p[skill->5]
    ==>p[skill->3]

The new more consistent behavior is demonstrated below:

    gremlin> g.E().properties().count()
    ==>13
    gremlin> g.E().properties()
    ==>p[since->2009]
    ==>p[since->2010]
    ==>p[skill->4]
    ==>p[skill->5]
    ==>p[since->2010]
    ==>p[since->2011]
    ==>p[skill->5]
    ==>p[skill->4]
    ==>p[since->2012]
    ==>p[skill->3]
    ==>p[skill->3]
    ==>p[skill->5]
    ==>p[skill->3]
    gremlin> g.E().properties().dedup().count()
    ==>7
    gremlin> g.E().properties().dedup()
    ==>p[since->2009]
    ==>p[since->2010]
    ==>p[skill->4]
    ==>p[skill->5]
    ==>p[since->2011]
    ==>p[since->2012]
    ==>p[skill->3]

See: TINKERPOP-2318

### Upgrading for Providers

#### Graph Driver Providers

##### GraphBinary API Change

In GraphBinary serialization, Java `GraphBinaryReader` and `GraphBinaryWriter`, along with `TypeSerializer<T>` interface now take a `Buffer` instance instead of Netty’s `ByteBuf`, that way we avoid exposing Netty’s API in our own public API.

Using our own `Buffer` interface, wrapping Netty’s buffer API, allowed us to move `TypeSerializer<T>` implementations, the reader and the writer to `org.apache.tinkerpop.gremlin.structure.io.binary` package in `gremlin-core`.

Additionally, `GraphBinaryReader` and `GraphBinaryWriter` methods now throw an java’s `IOException`, instead of our own `SerializationException`.

See: TINKERPOP-2305

## TinkerPop 3.4.4

Release Date: October 14, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Python GraphBinary

There is now support for GraphBinary in Python. As with Java, it remains a working but experimental format that is still under evaluation. This new serializer can be used by first ensuring that it is available on the server and then configuring the connection as follows:

    from gremlin_python.driver.serializer import GraphBinarySerializersV1
    gremlin_server_url = "ws://172.17.0.2:45940/gremlin"
    remote_conn = DriverRemoteConnection(gremlin_server_url, 'g',
                                         message_serializer=GraphBinarySerializersV1())
    g = Graph().traversal().withRemote(remote_conn)

TINKERPOP-2279

#### elementMap() Step

Since graph elements (i.e. `Vertex`, `Edge`, and `VertexProperty`) are returned from remote sources as references (i.e. without properties), one of the more common needs for Gremlin users is the ability to easily return a `Map` representation of the elements that they are querying. Typically, such transformations are handled by `valueMap()`:

    gremlin> g.V().has('person','name','marko').valueMap(true)
    ==>[id:1,label:person,name:[marko],age:[29]]
    gremlin> g.V().has('person','name','marko').valueMap().by(unfold())
    ==>[name:marko,age:29]

or by way of `project()`:

    gremlin> g.V().has('person','name','marko').
    ......1>   project('name','age','vid','vlabel').
    ......2>     by('name').
    ......3>     by('age').
    ......4>     by(id).
    ......5>     by(label)
    ==>[name:marko,age:29,vid:1,vlabel:person]

While `valueMap()` works reasonably well for `Vertex` and `VertexProperty` transformations it does less well for `Edge` as it fails to include incident vertices:

    gremlin> g.E(11).valueMap(true)
    ==>[id:11,label:created,weight:0.4]

This limitation forces a fairly verbose use of `project()` for what is a reasonably common requirement:

    gremlin> g.E(12).union(valueMap(true),
    ......1>               project('inV','outV','inVLabel','outVLabel').
    ......2>                 by(inV().id()).
    ......3>                 by(outV().id()).
    ......4>                 by(inV().label()).
    ......5>                 by(outV().label())).unfold().
    ......6>               group().
    ......7>                 by(keys).
    ......8>                 by(select(values))
    ==>[inV:3,id:12,inVLabel:software,weight:0.2,outVLabel:person,label:created,outV:6]

By introducing `elementMap()`-step, there is now a single step that covers the most common transformation requirements for all three graph elements:

    gremlin> g.V().has('person','name','marko').elementMap()
    ==>[id:1,label:person,name:marko,age:29]
    gremlin> g.V().has('person','name','marko').elementMap('name')
    ==>[id:1,label:person,name:marko]
    gremlin> g.V().has('person','name','marko').properties('name').elementMap()
    ==>[id:0,key:name,value:marko]
    gremlin> g.E(11).elementMap()
    ==>[id:11,label:created,IN:[id:3,label:software],OUT:[id:4,label:person],weight:0.4]

See: TINKERPOP-2284, Reference Documentation

## TinkerPop 3.4.3

Release Date: August 5, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Deprecated store()

The `store()`-step and `aggregate()`-step do the same thing in different ways, where the former is lazy and the latter is eager in the side-effect collection of objects from the traversal. The different behaviors can be thought of as differing applications of `Scope` where `global` is eager and `local` is lazy. As a result, there is no need for both steps when one will do.

As of 3.4.3, `store(String)` is now deprecated in favor of `aggregate(Scope, String)` where the `Scope` should be set to `local` to ensure the same functionality as `store()`. Note that `aggregate('x')` is the same as `aggregate(global,'x')`.

See: TINKERPOP-1553

#### Deprecate Gryo in Gremlin Server

Gryo is now deprecated as a serialization format for Gremlin Server, however, it is still configured as a default option in the sample configuration files packaged with the server. The preferred serialization option should now be GraphBinary. Note that Gremlin Console is now configured to use GraphBinary by default.

See: TINKERPOP-2250

### Upgrading for Providers

#### Graph Driver Providers

##### Gremlin Server Test Configuration

Gremlin Server has a test configuration built into its Maven build process which all integration tests and Gremlin Language Variants use to validate their operations. While this approach has worked really well for test automation within Maven, there are often times where it would be helpful to simply have Gremlin Server running with that configuration. This need is especially true when developing Gremlin Language Variants which is something that is done outside of the JVM.

This release introduces a Docker script that will start Gremlin Server with this test configuration. It can be started with:

    docker/gremlin-server.sh

Once started, it is then possible to run GLV tests directly from a debugger against this instance which should hopefully reduce development friction.

see: Developer Documentation

## TinkerPop 3.4.2

Release Date: May 28, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Per Request Options

In 3.4.0, the notion of `RequestOptions` were added so that users could have an easier way to configure settings on individual requests made through the Java driver. While that change provided a way to set those configurations for script based requests, it didn’t include options to make those settings in a `Traversal` submitted via `Bytecode`. In this release those settings become available via `with()` step on the `TraversalSource` as follows:

    GraphTraversalSource g = traversal().withRemote(conf);
    List<Vertex> vertices = g.with(Tokens.ARGS_SCRIPT_EVAL_TIMEOUT, 500L).V().out("knows").toList()

See: TINKERPOP-2211

#### Gremlin Console Timeout

The Gremlin Console timeout that is set by `:remote config timeout x` was client-side only in prior versions, which meant that if the console timeout was less than the server timeout the client would timeout but the server might still be processing the request. Similarly, a longer timeout on the console would not change the server and the timeout would occur sooner than expected. These discrepancies often led to confusion.

As of 3.4.0, the Java Driver API allowed for timeout settings to be more easily passed per request, so the console was modified for this current version to pass the console timeout for each remote submission thus yielding more consistent and intuitive behavior.

See: TINKERPOP-2203

### Upgrading for Providers

#### Graph System Providers

##### Warnings

It is now possible to pass warnings over the Gremlin Server protocol using a `warnings` status attribute. The warnings are expected to be a string value or a `List` of string values which can be consumed by the user or tools that check for that status attribute. Note that Gremlin Console is one such tool that will respond to this status attribute - it will print the messages to the console as they are detected when doing remote script submissions.

See: TINKERPOP-2216

#### Graph Driver Providers

##### GraphBinary API Change

In GraphBinary serialization, Java `write()` and `writeValue()` from `TypeSerializer<T>` interface now take a Netty’s `ByteBuf` instance instead of an `ByteBufAllocator`, that way the same buffer instance gets reused during the write of a message. Additionally, we took the opportunity to remove the unused parameter from `ResponseMessageSerializer`.

See: TINKERPOP-2161

## TinkerPop 3.4.1

Release Date: March 18, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Mix SPARQL and Gremlin

In the initial release of `sparql-gremlin` it was only possible to execute a SPARQL query and have it translate to Gremlin. Therefore, it was only possible to write a query like this:

    gremlin> g.sparql("SELECT ?name ?age WHERE { ?person v:name ?name . ?person v:age ?age }")
    ==>[name:marko,age:29]
    ==>[name:vadas,age:27]
    ==>[name:josh,age:32]
    ==>[name:peter,age:35]
    gremlin> g.sparql("SELECT * WHERE { }")
    ==>v[1]
    ==>v[2]
    ==>v[3]
    ==>v[4]
    ==>v[5]
    ==>v[6]

In this release, however, it is now possible to further process that result with Gremlin steps:

    gremlin> g.sparql("SELECT ?name ?age WHERE { ?person v:name ?name . ?person v:age ?age }").select("name")
    ==>marko
    ==>vadas
    ==>josh
    ==>peter
    gremlin> g.sparql("SELECT * WHERE { }").out("knows").values("name")
    ==>vadas
    ==>josh

See: TINKERPOP-2171, Reference Documentation

### Upgrading for Providers

#### Graph Database Providers

##### GraphBinary Serializer Changes

In GraphBinary serialization, Java `write()` and `writeValue()` from `TypeSerializer<T>` interface now take a Netty’s `ByteBuf` instance instead of an `ByteBufAllocator`, that way the same buffer instance gets reused during the write of a message. Additionally, we took the opportunity to remove the unused parameter from `ResponseMessageSerializer`.

See: TINKERPOP-2161

## TinkerPop 3.4.0

Release Date: January 2, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### sparql-gremlin

The `sparql-gremlin` module is a SPARQL to Gremlin compiler, which allows SPARQL to be executed over any TinkerPop-enabled graph system.

    graph = TinkerFactory.createModern()
    g = graph.traversal(SparqlTraversalSource)
    g.sparql("""SELECT ?name ?age
                WHERE { ?person v:name ?name . ?person v:age ?age }
                ORDER BY ASC(?age)""")

See: TINKERPOP-1878, Reference Documentation

#### Gremlin.NET Driver Improvements

The Gremlin.NET driver now uses request pipelining. This allows connections to be reused for different requests in parallel which should lead to better utilization of connections. The `ConnectionPool` now also has a fixed size whereas it could previously create an unlimited number of connections. Each `Connection` can handle up to `MaxInProcessPerConnection` requests in parallel. If this limit is reached for all connections, then a `NoConnectionAvailableException` is thrown which makes this a breaking change.

These settings can be set as properties on the `ConnectionPoolSettings` instance that can be passed to the `GremlinClient`.

See: TINKERPOP-1774, TINKERPOP-1775, Reference Documentation

#### Indexing of Collections

TinkerPop 3.4.0 adds a new `index()`-step, which allows users to transform simple collections into index collections or maps.

    gremlin> g.V().hasLabel("software").values("name").fold().
    ......1>   order(local).
    ......2>   index().unfold()
    ==>[lop,0]
    ==>[ripple,1]
    gremlin> g.V().hasLabel("person").values("name").fold().
    ......1>   order(local).by(decr).
    ......2>   index().
    ......3>     with(WithOptions.indexer, WithOptions.map)
    ==>[0:vadas,1:peter,2:marko,3:josh]

#### Modulation of valueMap()

The `valueMap()` step now supports `by` and `with` modulation, which also led to the deprecation of `valueMap(true)` overloads.

##### by() Modulation

With the help of the `by()` modulator `valueMap()` result values can now be adjusted, which is particularly useful to turn multi-/list-values into single values.

    gremlin> g.V().hasLabel("person").valueMap()
    ==>[name:[marko],age:[29]]
    ==>[name:[vadas],age:[27]]
    ==>[name:[josh],age:[32]]
    ==>[name:[peter],age:[35]]
    gremlin> g.V().hasLabel("person").valueMap().by(unfold())
    ==>[name:marko,age:29]
    ==>[name:vadas,age:27]
    ==>[name:josh,age:32]
    ==>[name:peter,age:35]

##### with() Modulation

The `with()` modulator can be used to include certain tokens (`id`, `label`, `key` and/or `value`).

The old way (still valid, but deprecated):

    gremlin> g.V().hasLabel("software").valueMap(true)
    ==>[id:10,label:software,name:[gremlin]]
    ==>[id:11,label:software,name:[tinkergraph]]
    gremlin> g.V().has("person","name","marko").properties("location").valueMap(true)
    ==>[id:6,key:location,value:san diego,startTime:1997,endTime:2001]
    ==>[id:7,key:location,value:santa cruz,startTime:2001,endTime:2004]
    ==>[id:8,key:location,value:brussels,startTime:2004,endTime:2005]
    ==>[id:9,key:location,value:santa fe,startTime:2005]

The new way:

    gremlin> g.V().hasLabel("software").valueMap().with(WithOptions.tokens)
    ==>[id:10,label:software,name:[gremlin]]
    ==>[id:11,label:software,name:[tinkergraph]]
    gremlin> g.V().has("person","name","marko").properties("location").valueMap().with(WithOptions.tokens)
    ==>[id:6,key:location,value:san diego,startTime:1997,endTime:2001]
    ==>[id:7,key:location,value:santa cruz,startTime:2001,endTime:2004]
    ==>[id:8,key:location,value:brussels,startTime:2004,endTime:2005]
    ==>[id:9,key:location,value:santa fe,startTime:2005]

Furthermore, now there’s a finer control over which of the tokens should be included:

    gremlin> g.V().hasLabel("software").valueMap().with(WithOptions.tokens, WithOptions.labels)
    ==>[label:software,name:[gremlin]]
    ==>[label:software,name:[tinkergraph]]
    gremlin> g.V().has("person","name","marko").properties("location").valueMap().with(WithOptions.tokens, WithOptions.values)
    ==>[value:san diego,startTime:1997,endTime:2001]
    ==>[value:santa cruz,startTime:2001,endTime:2004]
    ==>[value:brussels,startTime:2004,endTime:2005]
    ==>[value:santa fe,startTime:2005]

As shown above, the support of the `with()` modulator for `valueMap()` makes the `valueMap(boolean)` overload superfluous, hence this overload is now deprecated. This is a breaking API change, since `valueMap()` will now always yield instances of type `Map<Object, Object>`. Prior this change only the `valueMap(boolean)` overload yielded `Map<Object, Object>` objects, `valueMap()` without the boolean parameter used to yield instances of type `Map<String, Object>`.

See: TINKERPOP-2059

#### Predicate Number Comparison

In previous versions `within()` and `without()` performed strict number comparisons; that means these predicates did not only compare number values, but also the type. This was inconsistent with how other predicates (like `eq`, `gt`, etc.) work. All predicates will now ignore the number type and instead compare numbers only based on their value.

Old behavior:

    gremlin> g.V().has("age", eq(32L))
    ==>v[4]
    gremlin> g.V().has("age", within(32L, 35L))
    gremlin>

New behavior:

    gremlin> g.V().has("age", eq(32L))
    ==>v[4]
    gremlin> g.V().has("age", within(32L, 35L))
    ==>v[4]
    ==>v[6]

See: TINKERPOP-2058

#### ReferenceElementStrategy

Gremlin Server has had some inconsistent behavior in the serialization of the results it returns. Remote traversals based on Gremlin bytecode always detach returned graph elements to "reference" (i.e. removes properties and only include the `id` and `label`), but scripts would detach graph elements and include the properties. For 3.4.0, TinkerPop introduces the `ReferenceElementStrategy` which can be configured on a `GraphTraversalSource` to always detach to "reference".

    gremlin> graph = TinkerFactory.createModern()
    ==>tinkergraph[vertices:6 edges:6]
    gremlin> g = graph.traversal().withStrategies(ReferenceElementStrategy.instance())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> v = g.V().has('person','name','marko').next()
    ==>v[1]
    gremlin> v.class
    ==>class org.apache.tinkerpop.gremlin.structure.util.reference.ReferenceVertex
    gremlin> v.properties()
    gremlin>

The packaged initialization scripts that come with Gremlin Server now pre-configure the sample graphs with this strategy to ensure that both scripts and bytecode based requests over any protocol (HTTP, websocket, etc) and serialization format all return a "reference". To revert to the old form, simply remove the strategy in the initialization script.

It is recommended that users choose to configure their `GraphTraversalSource` instances with `ReferenceElementStrategy` as working with "references" only is the recommended method for developing applications with TinkerPop. In the future, it is possible that `ReferenceElementStrategy` will be configured by default for all graphs on or off Gremlin Server, so it would be best to start utilizing it now and grooming existing Gremlin and related application code to account for it.

See: TINKERPOP-2075

#### Text Predicates

Gremlin now supports simple text predicates on top of the existing `P` predicates. Both, the new `TextP` text predicates and the old `P` predicates, can be chained using `and()` and `or()`.

    gremlin> g.V().has("person","name", containing("o")).valueMap()
    ==>[name:[marko],age:[29]]
    ==>[name:[josh],age:[32]]
    gremlin> g.V().has("person","name", containing("o").and(gte("j").and(endingWith("ko")))).valueMap()
    ==>[name:[marko],age:[29]]

See: TINKERPOP-2041

#### Changed Infix Behavior

The infix notation of `and()` and `or()` now supports an arbitrary number of traversals and `ConnectiveStrategy` produces a traversal with proper AND and OR semantics.

    Input: a.or.b.and.c.or.d.and.e.or.f.and.g.and.h.or.i

    *BEFORE*
    Output: or(a, or(and(b, c), or(and(d, e), or(and(and(f, g), h), i))))

    *NOW*
    Output: or(a, and(b, c), and(d, e), and(f, g, h), i)

Furthermore, previous versions failed to apply 3 or more `and()` steps using the infix notation, this is now fixed.

    gremlin> g.V().has("name","marko").and().has("age", lt(30)).or().has("name","josh").and().has("age", gt(30)).and().out("created")
    ==>v[1]
    ==>v[4]

See: TINKERPOP-2029

#### GraphBinary

GraphBinary is a new language agnostic, network serialization format designed to replace Gryo and GraphSON. At this time it is only available on the JVM, but support will be added for other languages in upcoming releases. The serializer has been configured in Gremlin Server’s packaged configuration files. The serializer can be configured using the Java driver as follows:

    Cluster cluster = Cluster.build("localhost").port(8182).
                              serializer(Serializers.GRAPHBINARY_V1D0).create();
    Client client = cluster.connect();
    List<Result> r = client.submit("g.V().has('person','name','marko')").all().join();

See: TINKERPOP-1942, IO Documentation

#### Status Attributes

The Gremlin Server protocol allows for status attributes to be returned in responses. These attributes were typically for internal use, but were designed with extensibility in mind so that providers could place return their own attributes to calling clients. Unfortunately, unless the client was being used with protocol level requests (which wasn’t convenient) those attributes were essentially hidden from view. As of this version however, status attributes are fully retrievable for both successful requests and exceptions.

See: TINKERPOP-1913

#### with() Step

This version of TinkerPop introduces the `with()`-step to Gremlin. It isn’t really a step but is instead a step modulator. This modulator allows the step it is modifying to accept configurations that can be used to alter the behavior of the step itself. A good example of its usage is shown with the revised syntax of the `pageRank()`-step which now uses `with()` to replace the old `by()` options:

    g.V().hasLabel('person').
      pageRank().
        with(PageRank.edges, __.outE('knows')).
        with(PageRank.propertyName, 'friendRank').
      order().
        by('friendRank',desc).
      valueMap('name','friendRank')

A similar change was made for `peerPressure()`-step:

    g.V().hasLabel('person').
      peerPressure().
        with(PeerPressure.propertyName, 'cluster').
      group().
        by('cluster').
        by('name')

Note that the `by()` modulators still work, but should be considered deprecated and open for removal in a future release where breaking changes are allowed.

See: TINKERPOP-1975, Reference Documentation

#### shortestPath() Step

Calculating the shortest path between vertices is a common graph use case. While the traversal to determine a shortest path can be expressed in Gremlin, this particular problem is common enough that the feature has been encapsulated into its own step, demonstrated as follows:

    gremlin> g.withComputer().V().has('name','marko').
    ......1>   shortestPath().with(ShortestPath.target, has('name','peter'))
    ==>[v[1],v[3],v[6]]

See: TINKERPOP-1990, Reference Documentation

#### connectedComponent() Step

In prior version of TinkerPop, it was recommended that the identification of Connected Component instances in a graph be computed by way of a reasonably complex bit of Gremlin that looked something like this:

    g.V().emit(cyclicPath().or().not(both())).repeat(both()).until(cyclicPath()).
      path().aggregate("p").
      unfold().dedup().
      map(__.as("v").select("p").unfold().
             filter(unfold().where(eq("v"))).
             unfold().dedup().order().by(id).fold()).
      dedup()

The above approach had a number of drawbacks that included a large execution cost as well as incompatibilities in OLAP. To simplify usage of this commonly use graph algorithm, TinkerPop 3.4.0 introduces the `connectedComponent()` step which reduces the above operation to:

    g.withComputer().V().connectedComponent()

It is important to note that this step does require the use of a `GraphComputer` to work, as it utilizes a `VertexProgram` behind the scenes.

See: TINKERPOP-1967, Reference Documentation

#### io() Step

There have been some important changes to IO operations for reading and writing graph data. The use of `Graph.io()` has been deprecated to further remove dependence on the Graph (Structure) API for users and to extend these basic operations to GLV users by making these features available as part of the Gremlin language.

It is now possible to simply use Gremlin:

    graph = ...
    g = graph.traversal()
    g.io(someInputFile).read().iterate()
    g.io(someOutputFile).write().iterate()

While `io()`-step is still single-threaded for OLTP style loading, it can be utilized in conjunction with OLAP which internally uses `CloneVertexProgram` and therefore any graph `InputFormat` or `OutputFormat` can be configured in conjunction with this step for parallel loads of large datasets.

It is also worth noting that the `io()`-step may be overridden by graph providers to utilize their native bulk-loading features, so consult the documentation of the implementation being used to determine if there are any improved efficiencies there.

See: TINKERPOP-1996, Reference Documentation

#### Per Request Options

The Java driver now allows for various options to be set on a per-request basis via new overloads to `submit()` that accept `RequestOption` instances. A good use-case for this feature is to set a per-request override to the `scriptEvaluationTimeout` so that it only applies to the current request.

    Cluster cluster = Cluster.open();
    Client client = cluster.connect();
    RequestOptions options = RequestOptions.build().timeout(500).create();
    List<Result> result = client.submit("g.V()", options).all().get();

See: TINKERPOP-1342

#### min() max() and Comparable

Previously `min()` and `max()` were only working for numeric values. This has been changed and these steps can now operate over any `Comparable` value. The common workaround was the combination of `order().by()` and `limit()` as shown here:

    gremlin> g.V().values('name').order().by().limit(1)      // workaround for min()
    ==>josh
    gremlin> g.V().values('name').order().by(decr).limit(1)  // workaround for max()
    ==>vadas

Any attempt to use `min()` or `max()` on non-numeric values lead to an exception:

    gremlin> g.V().values('name').min()
    java.lang.String cannot be cast to java.lang.Number
    Type ':help' or ':h' for help.
    Display stack trace? [yN]

With the changes in this release these kind of queries became a lot easier:

    gremlin> g.V().values('name').min()
    ==>josh
    gremlin> g.V().values('name').max()
    ==>vadas

#### Nested Loop Support

Traversals now support nesting of `repeat()` loops.

These can now be used to repeat another traversal while in a looped context, either inside the body of a `repeat()` or in its step modifiers (`until()` or `emit()`).

    gremlin> g.V().repeat(__.in('traverses').repeat(__.in('develops')).emit()).emit().values('name')
    ==>stephen
    ==>matthias
    ==>marko

See: TINKERPOP-967

#### EventStrategy API

There were some minor modifications to how `EventStrategy` is constructed and what can be expected from events raised from the addition of new properties.

With respect to the change in terms of `EventStrategy` construction, the `detach()` builder method formerly took a `Class` as an argument and that `Class` was meant to be one of the various "detachment factories" or `null`. That approach was a bit confusing, so that signature has changed to `detach(EventStrategy.Detachment)` where the argument is a more handy enum of detachment options.

As for the changes related to events themselves, it is first worth noting that the previously deprecated `vertexPropertyChanged(Vertex, Property, Object, Object…​)` on `MutationListener` has been removed for what should have originally been the correct signature of `vertexPropertyChanged(Vertex, VertexProperty, Object, Object…​)`. In prior versions when this method and its related `edgePropertyChanged()` and `vertexPropertyPropertyChanged()` were triggered by way of the addition of a new property a "fake" property was included with a `null` value for the "oldValue" argument to these methods (as it did not exist prior to this event). That was a bit awkward to reason about when dealing with that event. To make this easier, the event now raises with a `KeyedVertexProperty` or `KeyedProperty` instance, which only contains a property key and no value in them.

TINKERPOP-1831

#### Reducing Barrier Steps

The behavior of `min()`, `max()`, `mean()` and `sum()` has been modified to return no result if there’s no input. Previously these steps yielded the internal seed value:

    gremlin> g.V().values('foo').min()
    ==>NaN
    gremlin> g.V().values('foo').max()
    ==>NaN
    gremlin> g.V().values('foo').mean()
    ==>NaN
    gremlin> g.V().values('foo').sum()
    ==>0

These traversals will no longer emit a result. Note, that this also affects more complex scenarios, e.g. if these steps are used in `by()` modulators:

    gremlin> g.V().group().
    ......1>   by(label).
    ......2>   by(outE().values("weight").sum())
    ==>[software:0,person:3.5]

Since software vertices have no outgoing edges and thus no weight values to sum, `software` will no longer show up in the result. In order to get the same result as before, one would have to add a `coalesce()`-step:

    gremlin> g.V().group().
    ......1>   by(label).
    ......2>   by(outE().values("weight").sum())
    ==>[person:3.5]
    gremlin> g.V().group().
    ......1>   by(label).
    ......2>   by(coalesce(outE().values("weight"), constant(0)).sum())
    ==>[software:0,person:3.5]

See: TINKERPOP-1777

#### Order of select() Scopes

The order of select scopes has been changed to: maps, side-effects, paths. Previously the order was: side-effects, maps, paths - which made it almost impossible to select a specific map entry if a side-effect with the same name existed.

The following snippets illustrate the changed behavior:

    gremlin> g.V(1).
    ......1>   group("a").
    ......2>     by(__.constant("a")).
    ......3>     by(__.values("name")).
    ......4>   select("a")
    ==>[a:marko]
    gremlin> g.V(1).
    ......1>   group("a").
    ......2>     by(__.constant("a")).
    ......3>     by(__.values("name")).
    ......4>   select("a").select("a")
    ==>[a:marko]

Above is the old behavior; the second `select("a")` has no effect, it selects the side-effect `a` again, although one would expect to get the map entry `a`. What follows is the new behavior:

    gremlin> g.V(1).
    ......1>   group("a").
    ......2>     by(__.constant("a")).
    ......3>     by(__.values("name")).
    ......4>   select("a")
    ==>[a:marko]
    gremlin> g.V(1).
    ......1>   group("a").
    ......2>     by(__.constant("a")).
    ......3>     by(__.values("name")).
    ......4>   select("a").select("a")
    ==>marko

See: TINKERPOP-1522

#### GraphSON BulkSet

In earlier versions of TinkerPop, `BulkSet` was coerced to a `List` for GraphSON which was convenient in that it didn’t add a new data type to support, but inconvenient in that it meant that certain process tests were not consistent in terms of how they ran and the benefits of the `BulkSet` were "lost" in that the "bulk" was being resolved server side. With the addition of `BulkSet` as a GraphSON type the "bulk" is now resolved on the client side by the language variant. How that resolution occurs depends upon the language variant. For Java, there is a `BulkSet` object which maintains that structure sent from the server. For the other variants, the `BulkSet` is deserialized to a `List` form which results in a much larger memory footprint than what is contained the `BulkSet`.

See: TINKERPOP-2111

#### Python Bindings

Bindings were formerly created using a Python 2-tuple as a bit of syntactic sugar, but all other language variants used an explicit `Bindings` object which `gremlin-python` already had in place. To make all work variants behave consistently, the 2-tuple syntax has been removed in favor of the explicit `Bindings.of()` option.

    g.V(Bindings.of('id',1)).out('created').map(lambda: ("it.get().value('name').length()", "gremlin-groovy")).sum()

See: TINKERPOP-2116

#### Deprecation and Removal

This section describes newly deprecated classes, methods, components and patterns of usage as well as which previously deprecated features have been officially removed or repurposed.

##### Moving of RemoteGraph

`RemoteGraph` was long ago deprecated in favor of `withRemote()`. It became even less useful with the introduction of the `AnonymousTraversalSource` concept in 3.3.5. It’s only real use was for testing remote bytecode based traversals in the test suite as the test suite requires an actual `Graph` object to function properly. As such, `RemoteGraph` has been moved to `gremlin-test`. It should no longer be used in any capacity besides that.

See: TINKERPOP-2079

##### Removal of Giraph Support

Support for Giraph has been removed as of this version. There were a number of reasons for this decision which were discussed in the community prior to taking this step. Users should switch to Spark for their OLAP based graph-computing needs.

See: TINKERPOP-1930

##### Removal of Rebindings Options

The "rebindings" option is no longer supported for clients. It was deprecated long ago at 3.1.0. The server will not respond to them on any channel - websockets, nio or HTTP. Use the "aliases" option instead.

TINKERPOP-1705

##### gremlin-server.sh -i Removal

The `-i` option for installing dependencies in Gremlin Server was long ago deprecated and has now been removed. Please use `install` as its replacement going forward.

TINKERPOP-2031

##### Deprecation Removal

The following deprecated classes, methods or fields have been removed in this version:

- `gremlin-core`

  - `org.apache.tinkerpop.gremlin.jsr223.ImportCustomizer#GREMLIN_CORE`

  - `org.apache.tinkerpop.gremlin.process.remote.RemoteGraph` - moved to `gremlin-test`

  - `org.apache.tinkerpop.gremlin.process.remote.RemoteConnection.submit(Traversal)`

  - `org.apache.tinkerpop.gremlin.process.remote.RemoteConnection.submit(Bytecode)`

  - `org.apache.tinkerpop.gremlin.process.remote.traversal.strategy.decoration.RemoteStrategy#identity()`

  - `org.apache.tinkerpop.gremlin.process.traversal.TraversalEngine`

  - `org.apache.tinkerpop.gremlin.process.traversal.engine.*`

  - `org.apache.tinkerpop.gremlin.process.traversal.strategy.decoration.PartitionStrategy.Builder#addReadPartition(String)`

  - `org.apache.tinkerpop.gremlin.process.traversal.strategy.decoration.SubgraphStrategy.Builder#edgeCriterion(Traversal)`

  - `org.apache.tinkerpop.gremlin.process.traversal.strategy.decoration.SubgraphStrategy.Builder#vertexCriterion(Traversal)`

  - `org.apache.tinkerpop.gremlin.process.traversal.step.map.LambdaCollectingBarrierStep.Consumers`

  - `org.apache.tinkerpop.gremlin.process.traversal.step.util.HasContainer#makeHasContainers(String, P)`

  - `org.apache.tinkerpop.gremlin.process.traversal.step.util.event.MutationListener#vertexPropertyChanged(Vertex, Property, Object, Object…​)`

  - `org.apache.tinkerpop.gremlin.structure.Element.Exceptions#elementAlreadyRemoved(Class, Object)`

  - `org.apache.tinkerpop.gremlin.structure.Graph.Exceptions#elementNotFound(Class, Object)`

  - `org.apache.tinkerpop.gremlin.structure.Graph.Exceptions#elementNotFound(Class, Object, Exception)`

- `gremlin-driver`

  - `org.apache.tinkerpop.gremlin.driver.Client#rebind(String)`

  - `org.apache.tinkerpop.gremlin.driver.Client.ReboundClusterdClient`

  - `org.apache.tinkerpop.gremlin.driver.Tokens#ARGS_REBINDINGS`

- `gremlin-groovy`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine.close()` - no longer implements `AutoCloseable`

- `gremlin-server`

  - `org.apache.tinkerpop.gremlin.server.GraphManager#getGraphs()`

  - `org.apache.tinkerpop.gremlin.server.GraphManager#getTraversalSources()`

  - `org.apache.tinkerpop.gremlin.server.Settings#serializedResponseTimeout`

  - `org.apache.tinkerpop.gremlin.server.Settings.AuthenticationSettings#className`

  - `org.apache.tinkerpop.gremlin.server.handler.OpSelectorHandler(Settings, GraphManager, GremlinExecutor, ScheduledExecutorService)`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractOpProcessor#makeFrame(ChannelHandlerContext, RequestMessage, MessageSerializer serializer, boolean, List, ResponseStatusCode code)`

- `hadoop-graph`

  - `org.apache.tinkerpop.gremlin.hadoop.structure.HadoopConfiguration#getGraphInputFormat()`

  - `org.apache.tinkerpop.gremlin.hadoop.structure.HadoopConfiguration#getGraphOutputFormat()`

Please see the javadoc deprecation notes or upgrade documentation specific to when the deprecation took place to understand how to resolve this breaking change.

See: TINKERPOP-1143, TINKERPOP-1296, TINKERPOP-1705, TINKERPOP-1707, TINKERPOP-1954, TINKERPOP-1986, TINKERPOP-2079, TINKERPOP-2103

##### Deprecated GraphSONMessageSerializerGremlinV2d0

The `GraphSONMessageSerializerGremlinV2d0` serializer is now analogous to `GraphSONMessageSerializerV2d0` and therefore redundant. It has technically always been equivalent in terms of functionality as both serialized to the same format (i.e. GraphSON 2.0 with embedded types). It is no longer clear why these two classes were established this way, but it does carry the negative effect where multiple serializer versions could not be bound to Gremlin Server’s HTTP endpoint as the MIME types conflicted on `application/json`. By simply making both message serializers support `application/json` and `application/vnd.gremlin-v2.0+json`, it then became possible to overcome that limitation. In short, prefer use of `GraphSONMessageSerializerV2d0` when possible.

Note that this is a breaking change in the sense that `GraphSONMessageSerializerV2d0` will no longer set the header of requests messages to `application/json`. As a result, older versions of Gremlin Server not configured with `GraphSONMessageSerializerGremlinV2d0` will not find a deserializer to match the request.

See: TINKERPOP-1984

##### Removed groovy-sql Dependency

Gremlin Console and Gremlin Server no longer include groovy-sql. If you depend on groovy-sql, you can install it in Gremlin Console or Gremlin Server using the plugin system.

Console:

    :install org.codehaus.groovy groovy-sql 2.5.2

Server:

    bin/gremlin-server.sh install org.codehaus.groovy groovy-sql 2.5.2

If your project depended on groovy-sql transitively, simply include it in your project’s build file (e.g. maven: pom.xml).

See: TINKERPOP-2037

### Upgrading for Providers

#### Graph Database Providers

##### io() Step

The new `io()`-step that was introduced provides some new changes to consider. Note that `Graph.io()` has been deprecated and users are no longer instructed to utilize that method. It is not yet decided when that method will be removed completely, but given the public nature of it and the high chance of common usage, it should be hanging around for some time.

As with any step in Gremlin, it is possible to replace it with a more provider specific implementation that could be more efficient. Developing a `TraversalStrategy` to do this is encouraged, especially for those graph providers who might have special bulk loaders that could be abstracted by this step. Examples of this are already shown with `HadoopGraph` which replaces the simple single-threaded loader with `CloneVertexProgram`. Graph providers are encouraged to use the `with()` step to capture any necessary configurations required for their underlying loader to work. Graph providers should not feel restricted to `graphson`, `gryo` and `graphml` formats either. If a graph supports CSV or some custom graph specific format, it shouldn’t be difficult to gather the configurations necessary to make that available to users.

See: TINKERPOP-1996

##### Caching Graph Features

For graph implementations that have expensive creation times, it can be time consuming to run the TinkerPop test suite as each test run requires a `Graph` instance even if the test is ultimately ignored becaue it doesn’t pass the feature checks. To possibly help alleviate this problem, the `GraphProvider` interface now includes this method:

    public default Optional<Graph.Features> getStaticFeatures() {
        return Optional.empty();
    }

This method can be implemented to return a cacheable set of features for a `Graph` generated from that `GraphProvider`. Assuming this method is faster than the cost of creating a new `Graph` instance, the test suite should execute significantly faster depending on how many tests end up being ignored.

See: TINKERPOP-1518

##### Configuring Interface

There were some changes to interfaces that were related to `Step`. A new `Configuring` interface was added that was helpful in the implementation of the `with()`-step modulator. This new interface extends the `Parameterizing` interface (which moved to the `org.apache.tinkerpop.gremlin.process.traversal.step` package with the other step interfaces) and in turn is extended by the `Mutating` interface. Making this change meant that the `Mutating.addPropertyMutations()` method could be removed in favor of the new `Configuring.configure()` method.

All of the changes above basically mean, that if the `Mutating` interface was being used in prior versions, the `addPropertyMutations()` method simply needs to be changed to `configure()`.

See: TINKERPOP-1975

##### OptionsStrategy

`OptionsStrategy` is a `TraversalStrategy` that makes it possible for users to set arbitrary configurations on a `Traversal`. These configurations can be used by graph providers to allow for traversal-level configurations to be accessible to their custom steps. A user would write something like:

    g.withStrategies(OptionsStrategy.build().with("specialLimit", 10000).create()).V();

The `OptionsStrategy` is really only the carrier for the configurations and while users can choose to utilize that more verbose method for constructing it shown above, it is more elegantly constructed as follows using `with()`-step:

    g.with("specialLimit", 10000)).V();

The graph provider could then access that value of "specialLimit" in their custom step (or elsewhere) as follows:

    OptionsStrategy strategy = this.getTraversal().asAdmin().getStrategies().getStrategy(OptionsStrategy.class).get();
    int specialLimit = (int) strategy.getOptions().get("specialLimit");

See: TINKERPOP-2053

##### Removed hadoop-gremlin Test Artifact

The `hadoop-gremlin` module no longer generates a test jar that can be used as a test dependency in other modules. Generally speaking, that approach tends to be a bad practice and can cause build problems with Maven that aren’t always obvious to troubleshoot. With the removal of `giraph-gremlin` for 3.4.0, it seemed even less useful to have this test artifact present. All tests are still present. The follow provides a basic summary of how this refactoring occurred:

- A new `AbstractFileGraphProvider` was created in `gremlin-test` which provided a lot of the features that `HadoopGraphProvider` was exposing. Both `HadoopGraphProvider` and `SparkHadoopGraphProvider` extend from that class now.

- `ToyIoRegistry` and related classes were moved to `gremlin-test`.

- The various tests that validated capabilities of `Storage` have been moved to `spark-gremlin` and are part of those tests now. Obviously, that makes those tests specific to Spark testing now. If that location creates a problem for some reason, that decision can be revisited at some point.

See: TINKERPOP-1410

##### TraversalEngine Moved

The `TraversalEngine` interface was deprecated in 3.2.0 along with all related methods that used it and classes that implemented it. It was replaced by the `Computer` interface and provided a much nicer way to plug different implementations of `Computer` into a traversal. `TraversalEngine` was never wholly removed however as it had some deep dependencies in the inner workings of the test suite. That infrastructure has largely remained as is until now.

As of 3.4.0, `TraversalEngine` is no longer in `gremlin-core` and can instead be found in `gremlin-test` as it is effectively a "test-only" component and serves no other real function. As explained in the javadocs going back to 3.2.0, providers should implement the `Computer` class and use that instead. At this point, graph providers should have long ago moved to the `Computer` infrastructure as methods for constructing a `TraversalSource` with a `TraversalEngine` were long ago removed.

See: TINKERPOP-1143

##### Upsert Graph Feature

Some `Graph` implementations may be able to offer upsert functionality for vertices and edges, which can help improve usability and performance. To help make it clear to users that a graph operates in this fashion, the `supportsUpsert()` feature has been added to both `Graph.VertexFeatures` and `Graph.EdgeFeatures`. By default, both of these methods will return `false`.

Should a provider wish to support this feature, the behavior of `addV()` and/or `addE()` should change such that when a vertex or edge with the same identifier is provided, the respective step will insert the new element if that value is not present or update an existing element if it is found. The method by which the provider "identifies" an element is completely up to the capabilities of that provider. In the most simple fashion, a graph could simply check the value of the supplied `T.id`, however graphs that support some form of schema will likely have other methods for determining whether or not an existing element is present.

The extent to which TinkerPop tests "upsert" is fairly narrow. Graph providers that choose to support this feature should consider their own test suites carefully to ensure appropriate coverage.

See: TINKERPOP-1685

##### TypeTranslator Changes

The `TypeTranslator` experienced a change in its API and `GroovyTranslator` a change in expectations.

`TypeTranslator` now implements `BiFunction` and takes the graph traversal source name as an argument along with the object to translate. This interface is implemented by default for Groovy with `GroovyTranslator.DefaultTypeTranslator` which encapsulates all the functionality of what `GroovyTranslator` formerly did by default. To provide customize translation, simply extend the `DefaultTypeTranslator` and override the methods.

`GroovyTranslator` now expects that the `TypeTranslator` provide to it as part of its `of()` static method overload is "complete" - i.e. that it provides all the functionality to translate the types passed to it. Thus, a "complete" `TypeTranslator` is one that does everything that `DefaultTypeTranslator` does as a minimum requirement. Therefore, the extension model described above is the easiest way to get going with a custom `TypeTranslator` approach.

See: TINKERPOP-2072

#### Graph Driver Providers

##### Deprecation Removal in RemoteConnection

The two deprecated synchronous `submit()` methods on the `RemoteConnection` interface have been removed, which means that `RemoteConnection` implementations will need to implement `submitAsync(Bytecode)` if they have not already done so.

See: TINKERPOP-2103

# TinkerPop 3.3.0

Gremlin Symphony #40 in G Minor

## TinkerPop 3.3.11

Release Date: June 1, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GLV Sessions

While TinkerPop doesn’t recommend the use of sessions for most use cases, it does remain a feature that is available and exposed on the server. As such, providing support in all Gremlin Language Variants for this feature is useful in ensuring a consistent implementation for all programming languages.

    const client = new Client('ws://localhost:8182/gremlin', { traversalSource: 'g', 'session': 'unique-string-id' });

    client = Client('ws://localhost:8182/gremlin', 'g', session=str(uuid.uuid4()))

    var gremlinServer = new GremlinServer("localhost", 8182);
    var client = new GremlinClient(gremlinServer, sessionId: Guid.NewGuid().ToString()))

#### Deprecate maxWaitForSessionClose

The `maxWaitForSessionClose` setting for the Java driver has been deprecated and in some sense replaced by the `maxWaitForClose` setting. The two settings perform different functions, but expect `maxWaitForSessionClose` to be removed in future versions. The `maxWaitForClose` performs a more useful function than `maxWaitForSessionClose` in the sense that it tells the driver how long it should wait for pending messages from the server before closing the connection. The `maxWaitForSessionClose` on the other hand is how long the driver should wait for the server to respond to a session close message (i.e. an actual response from the server). Waiting for that specific response to the session close message could result in the driver hanging on calls to `Client.close()` if there is a long run query running on the server and close message is stacked behind that in queue.

Future versions will remove support for that particular message and simply close the session when the connection is closed. As a result that setting will no longer be useful. The old setting is really only useful for connecting to older versions of the server prior to 3.3.11 that do not have the session shutdown hook bound to the close of the connection.

See: TINKERPOP-2336

### Upgrading for Providers

#### Gremlin Driver Providers

##### Session Close

The "close" message for the `SessionOpProcessor` is deprecated, however the functionality to accept the message remains in Gremlin Server and the functionality to send the message remains in the Java driver. The expectation is that support for the message will be removed from the driver in a future release, likely at 3.5.0. Server implementations starting at 3.3.11 should look to use the close of a connection to trigger the close of a session and its release of resources.

See: TINKERPOP-2336

## TinkerPop 3.3.10

Release Date: February 3, 2020

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Traversal Clone

Once a traversal has been executed (i.e. iterated) it’s internal state is such that it cannot be re-used:

    gremlin> t = g.V().count()
    ==>6
    gremlin> t
    gremlin>

To re-use a traversal it must be copied with `clone()` as follows:

    gremlin> t = g.V().count()
    ==>6
    gremlin> t.clone()
    ==>6
    gremlin> t.clone()
    ==>6

The ability to `clone()` has been exclusive to Java and was a missing component of other supported languages like Python, Javascript and .NET. This feature has now been added for all the language variants making the ability to re-use traversals consistent in all ecosystems.

See: TINKERPOP-2315

#### Deprecated Jython Support

Jython support in `gremlin-python` has been deprecated to focus on native Python 3.x support for 3.5.0 where Jython support will be wholly removed. This change does mean that TinkerPop will no longer support the ability to submit lambdas as native Python scripts. They will need to be submitted as Groovy and the library will be defaulted to do as such.

See: TINKERPOP-2322

## TinkerPop 3.3.9

Release Date: October 14, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### ReservedKeysVerificationStrategy

`ReservedKeysVerificationStrategy` is a new `VerificationStrategy` that can be used to help prevent traversals from adding property keys that are protected. They may be protected as a result of the key being a reserved keyword of the underlying graph system or they key may simply violate some standard conventions.

    gremlin> g.withStrategies(ReservedKeysVerificationStrategy.build().throwException().create()).addV('person').property("id",123)
    The provided traversal contains a AddVertexStartStep that is setting a property key to a reserved word: id
    Type ':help' or ':h' for help.
    Display stack trace? [yN]

TINKERPOP-2280

#### Javascript ResponseError

Gremlin Javascript now enables more robust error handling by way of a `ResponseError` which provides access to more information from the server. Specifically, it includes the `statusMessage` and `statusCode` which were formerly packed into the `Error.message` property, which meant that the error message string had to be parsed if there was a need to take a specific action based on that information. The `ResponseError` also includes the `statusAttributes` which is a `Map` object that will typically incorporate server `exceptions` and `stackTrace` keys, but could also include provider specific error information.

The original error messaging has remained unchanged and therefore users who were message parsing should not expect changes in behavior, however, future versions will eliminate the "overuse" of the `Error.message` property, so it is advised that users update their code to take advantage of the `ResponseError` features.

See: TINKERPOP-2285

#### Java Driver NoHostAvailableException

Expect a `NoHostAvailableException` rather than a more generic `TimeoutException` if the Java driver is unable to connect to a `Host`. This sort of failure can occur in a number of different scenarios, but can often occur when there are configuration problems with authentication and SSL, preventing the connection to the `Host` to be established.

TINKERPOP-2132

#### Deprecated scriptEvaluationTimeout

The `scriptEvaluationTimeout` controls the length of time a request is processed by Gremlin Server (or at its core, the `GremlinExecutor`). Of course, with the introduction of bytecode-based requests many versions ago, this naming has failed to make complete sense in more recent times. Therefore, `scriptEvaluationTimeout` has been deprecated and replaced by `evaluationTimeout`. Both configurations are still respected, but it is advised that users switch to `evaluationTimeout` as `scriptEvaluationTimeout` will be removed in a later version.

Note that when configuring Gremlin Server’s `evaluationTimeout` that the `scriptEvaluationTimeout` should be set to `-1` (the default) or else it will use that value in its initialization of the server and ignore the `evaluationTimeout`.

See: TINKERPOP-2213

## TinkerPop 3.3.8

Release Date: August 5, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Branch Steps Accept Predicates and Traversals

Prior to this version, branch steps (in particular `BranchStep` and `ChooseStep`) could only handle constant values and `Pick` tokens. Starting in this version, these steps will also accept predicates and traversals as show in the example below.

    gremlin> g = TinkerFactory.createModern().traversal()
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g.V().hasLabel("person").
    ......1>   group().
    ......2>     by("name").
    ......3>     by(branch(values("age")).
    ......4>          option(29, constant("almost old")).
    ......5>          option(__.is(32), constant("looks like josh")).
    ......6>          option(lt(29), constant("pretty young")).
    ......7>          option(lt(35), constant("younger than peter")).
    ......8>          option(gte(30), constant("pretty old")).
    ......9>          option(none, constant("mysterious")).fold()).
    .....10>   unfold()
    ==>peter=[pretty old]
    ==>vadas=[pretty young, younger than peter]
    ==>josh=[looks like josh, younger than peter, pretty old]
    ==>marko=[almost old, younger than peter]

See: TINKERPOP-1084

#### Python DateTime

With GraphSON, the `g:Date` is meant to represent a millisecond-precision offset from the unix epoch, but earlier version of Gremlin Python were using the timezone of the local system to handle serialization and deserialization, thus resulting in incorrect conversion. This issue is now resolved. It may be necessary to remove workarounds that have been introduced to combat this problem.

See: TINKERPOP-2264

#### JavaScript withComputer()

Gremlin-Javascript now supports `withComputer()` syntax, which means that it is now possible in Javascript to utilize Gremlin steps that require a `GraphComputer` to execute (e.g. `pageRank()` and `peerPressure()`).

See: TINKERPOP-2251

#### JavaScript and .NET hasNext()

There is now greater consistency across Gremlin Language Variants with `hasNext()` support added to both JavaScript and .NET. Note that in .NET, the proper method name follows C# capitalization semantics and is referred to as `HasNext()`.

See: TINKERPOP-1921

#### Deprecated getSideEffects()

`Traversal.getSideEffects()` has been deprecated for purposes of external calls by end-users. While the method is still present TinkerPop no longer guarantees its existence in future versions or consistency of its behavior, especially for Gremlin Language Variants and remote traversal execution. If this method is currently in use to gather side-effect results after traversal execution, please change such code to use `cap()`-step. For example, code like this:

    gremlin> t = g.V().hasLabel('person').aggregate('p').out('created')
    ==>v[3]
    ==>v[5]
    ==>v[3]
    ==>v[3]
    gremlin> t.getSideEffects().get('p')
    ==>v[1]
    ==>v[2]
    ==>v[4]
    ==>v[6]

should be converted to something like:

    gremlin> g.V().hasLabel('person').aggregate('p').out('created').union(fold(),cap('p'))
    ==>[v[3],v[3],v[3],v[5]]
    ==>[v[1],v[2],v[4],v[6]]

TINKERPOP-2265

#### EventStrategy

Prior TinkerPop 3.3.6 `EventStrategy` did not work with multi-properties. The `EventStrategy` behavior for single-valued properties has not changed; if a property is added to a multi-valued `VertexProperty`, then a `VertexPropertyChangedEvent` will be now be fired. The arguments passed to the event depend on the cardinality type.

`Cardinality.list` | Since properties will always be added and never be overwritten, the old property passed to the change event will always be an empty property.
`Cardinality.set` | The old property passed to the change event will be empty if no other property with the same value exists, otherwise, it will be the existing property.

See: TINKERPOP-2159

## TinkerPop 3.3.7

Release Date: May 28, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### JavaScript DSL Pattern

Gremlin DSL developers had to rely on monkey patching to build a Domain Specific Language in JavaScript. With this latest version, the process is a bit more elegant and largely handled by extending existing core classes of `Gremlin-JavaScript` which is a bit more in-line with other language variant patterns for DSL development.

See: TINKERPOP-2089, Reference Documentation

#### Gremlin Console Interrupt

There are occasions where a traversal (or other evaluation) takes longer than expected to complete. Common examples of these situations typically include:

- Accidentally executing `g.V()` (i.e. full graph scan) on a very large graph as an OLTP style traversal.

- Not terminating a `repeat()` properly which results in an infinite loop.

- Bad data might create a cycle in the graph where one wasn’t expected.

- Failing to properly bound a traversal’s path through one or more supernodes.

In earlier versions, the only option was to kill the Gremlin Console (typically with `ctrl+c`), but as of this version `ctrl+c` will be intercepted and attempt to interrupt whatever process is currently executing.

See TINKERPOP-2181

#### Removed gperfutils Dependency

Gremlin Console included references to:

    <dependency>
        <groupId>org.gperfutils</groupId>
        <artifactId>gbench</artifactId>
    </dependency>
    <dependency>
        <groupId>org.gperfutils</groupId>
        <artifactId>gprof</artifactId>
    </dependency

to provide some benchmarking and profiling tools for the Utilities Plugin. Neither project is well maintained at this point and given that TinkerPop has moved past the versions of Groovy that are supported by these tools it doesn’t make sense to retain the dependencies. Users who wish to continue to use these tools can obviously do so still by manually adding the dependencies to the Gremlin Console or with the following command:

    gremlin> :install org.gperfutils gbench <version>
    gremlin> :install org.gperfutils gprof <version>

and then import the appropriate classes and methods to use.

See: TINKERPOP-2182

### Upgrading for Providers

#### Graph Database Providers

##### Detection of Anti-Patterns

This release adds a strategy named `EdgeLabelVerificationStrategy`. The strategy will not be added by default to the traversal source, however, providers can add it explicitly to encourage (or enforce) users to always specify at least one edge label. `EdgeLabelVerificationStrategy` can be configured to either throw an exception if no edge label was specified, log a warning or do both.

    gremlin> // throw an exception if edge label was not specified
    gremlin> g = TinkerFactory.createModern().traversal().withStrategies(EdgeLabelVerificationStrategy.build().throwException().create())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g.V(1).out('knows')
    ==>v[2]
    ==>v[4]
    gremlin> g.V(1).out()
    The provided traversal contains a vertex step without any specified edge label: VertexStep(OUT,vertex)
    Type ':help' or ':h' for help.
    Display stack trace? [yN]

    gremlin> // log a warning if edge label was not specified (Log4j has to be configured properly)
    gremlin> g = TinkerFactory.createModern().traversal().withStrategies(EdgeLabelVerificationStrategy.build().logWarning().create())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g.V(1).out('knows')
    ==>v[2]
    ==>v[4]
    gremlin> g.V(1).out()
    WARN  org.apache.tinkerpop.gremlin.process.traversal.strategy.verification.EdgeLabelVerificationStrategy  - The provided traversal contains a vertex step without any specified edge label: VertexStep(OUT,vertex)
    ==>v[3]
    ==>v[2]
    ==>v[4]

See: TINKERPOP-2191

## TinkerPop 3.3.6

Release Date: March 18, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Anti-Patterns Documentation

The Gremlin Recipes documentation now has a new section which discusses anti-patterns in Gremlin. Its subsections detail commonly seen approaches to the Gremlin language which can lead to poorly written and/or under-performing traversals. The new Anti-Patterns Section can be found here.

See: TINKERPOP-2114

## TinkerPop 3.3.5

Release Date: January 2, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### AnonymousTraversalSource

The `AnonymousTraversalSource` provides for a more unified syntax for `TraversalSource` construction by placing greater user emphasis on the creation of the source rather than the `Graph` it is connected to. It has a number of different static `traversal()` methods available and when imported as:

    import static org.apache.tinkerpop.gremlin.process.traversal.AnonymousTraversalSource.traversal;

allows `TraversalSource` construction syntax such as:

    gremlin> g = traversal().withGraph(TinkerFactory.createModern())
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g = traversal().withRemote('conf/remote-graph.properties')
    ==>graphtraversalsource[emptygraph[empty], standard]
    gremlin> g = traversal().withRemote(DriverRemoteConnection.using('localhost',8182))
    ==>graphtraversalsource[emptygraph[empty], standard]

Typically, this syntax is used for "remote" traversal construction for bytecode based requests, but has the option to bind a local `Graph` instance to it as well. It doesn’t save much typing to do so obviously, so it may not be best used in that situation. Python, Javascript and .NET have similar syntax.

See: TINKERPOP-2078

#### Bytecode Command

The Gremlin Console now has a new `:bytecode` command to help users work more directly with Gremlin bytecode. The command is more of a debugging tool than something that would be used for every day purposes. It is sometimes helpful to look at Gremlin bytecode directly and the process for viewing it in human readable format is not a single step process. It is also not immediately clear how to convert bytecode to a Gremlin string. The `:bytecode` command aims to help with both of these issues:

    gremlin> g = TinkerFactory.createModern().traversal()
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> :bytecode from g.V().out('knows')  //1
    ==>{"@type":"g:Bytecode","@value":{"step":[["V"],["out","knows"]]}}
    gremlin> :bytecode translate g {"@type":"g:Bytecode","@value":{"step":[["V"],["out","knows"]]}} //2
    ==>g.V().out("knows")

See: TINKERPOP-2050, Reference Documentation - Console Commands

#### Configurable Class Map Cache

The "class map" cache in Gremlin Server (specifically the `GremlinGroovyScriptEngine`) that holds compiled scripts is now fully configurable via the `GroovyCompilerGremlinPlugin.classMapCacheSpecification`.

See: TINKERPOP-2038, Reference Documentation - Cache Management

#### RangeStep Optimizing Strategy

A new strategy named `EarlyLimitStrategy` was added. The strategy will try to find a better spot for any `RangeStep`, which is as early as possible in the traversal. If possible it will also merge multiple `RangeStep`s into a single one by recalculating the range for the first step and removing the second. If it turns out that the merge of two steps won’t produce a valid range (an empty result), then the `EarlyLimitStrategy` will remove the `RangeStep` instances and insert a `NoneStep` instead.

This strategy is particularly useful when a provider implementation generates the queries to the underlying database. By making sure that the ranges are applied as early as possible, we can ensure that the underlying database is only asked for the least amount of data necessary to continue the traversal evaluation.

### Upgrading for Providers

#### Graph Database Providers

##### OptOut on GraphProvider

It is not uncommon for those utilizing the TinkerPop test suite to have multiple configurations of their graph under test. The multiple configurations typically manifest as multiple `GraphProvider` implementations which supply the different configurations to test. It is sometimes the case, that a particular `Graph` configuration cannot support all of the tests in the suite at which point some less than straightforward approaches to dealing with that present as solutions.

It has always been possible to apply an `OptOut` annotation to a `Graph` instance, to avoid a particular test execution. It is now possible to apply that same `OptOut` to a `GraphProvider` instance for that same purpose. Hopefully, this feature will make multiple configuration testing easier.

## TinkerPop 3.3.4

Release Date: October 15, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Introducing Order.asc and Order.desc

The `Order` enum originally introduced `incr` for ascending order and `decr` for descending order. It’s not clear why they were named this way when common querying parlance would call for `asc` and `desc` for those respective cases. Note that `incr` and `decr` have not been removed - just deprecated and thus marked for future removal. Prefer `asc` and `desc` going forward when writing Gremlin and look to update existing code using the deprecated values.

See: TINKERPOP-1956

#### TimedInterrupt

In Gremlin Server, it is best not to use the `timedInterrupt` option on `GroovyCompilerGremlinPlugin` because it can compete with the `scriptEvaluationTimeout` setting and produce a different error path. Simply rely on `scriptEvaluationTimeout` as it covers both script evaluation time and result iteration time.

See: TINKERPOP-1778

## TinkerPop 3.3.3

Release Date: May 8, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Credential DSL Changes

The Credential DSL has been modified to work as a standard Java-based Gremlin DSL. The now deprecated old approach used a "graph wrapping" style that was developed long before the recommended method for building DSLs was published. Under this new model, the DSL is initialized via traversal as follows:

    CredentialTraversalSource credentials = graph.traversal(CredentialTraversalSource.class)
    credentials.user("stephen","password").iterate()
    credentials.users("stephen").valueMap().next()
    credentials.users().count().next()
    credentials.users("stephen").drop().iterate()

See: TINKERPOP-1903, Reference Documentation - Security

## TinkerPop 3.3.2

Release Date: April 2, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Python Sets

Graph traversals that return a `Set` from Java are now coerced to a `List` in Python. This change ensures that Python results match Java results for the same traversal. It is possible to see this problem in prior versions of gremlin-python where a `Set` of numbers of different types are returned. In Java, a set of:

    [1,1.0d,2,2.0d]

would be deserialized to the following in Python:

    [1,2]

Now that the Java `Set` is coerced to a `List` in Gremin Python, the Java `Set` can be fully represented. Users who require a `Set` will need to manually convert their `List` to a `Set`.

See: TINKERPOP-1844

## TinkerPop 3.3.1

Release Date: December 17, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Python path()

There was a bug in GraphSON 3.0 serialization that prevented proper handling of results contain `Path` object. As a result, traversals that used and returned results from the `path()`-step in Python would return unusable results, but did not actually cause an exception condition. This problem is now resolved.

See: TINKERPOP-1799

#### Added `math()`-step for Scientific Traversal Computing

`GraphTraversal.math(String)` was added. This step provides scientific calculator capabilities to a Gremlin traversal.

    gremlin> g.V().as('a').out('knows').as('b').math('a + b').by('age')
    ==>56.0
    ==>61.0
    gremlin> g.V().as('a').out('created').as('b').
    ......1>   math('b + a').
    ......2>     by(both().count().math('_ + 100')).
    ......3>     by('age')
    ==>132.0
    ==>133.0
    ==>135.0
    ==>138.0
    gremlin> g.withSack(1).V(1).repeat(sack(sum).by(constant(1))).times(10).emit().sack().math('sin _')
    ==>0.9092974268256817
    ==>0.1411200080598672
    ==>-0.7568024953079282
    ==>-0.9589242746631385
    ==>-0.27941549819892586
    ==>0.6569865987187891
    ==>0.9893582466233818
    ==>0.4121184852417566
    ==>-0.5440211108893698
    ==>-0.9999902065507035

See: TINKERPOP-1632

#### Changed Typing on `from()` and `to()`

The `from()` and `to()`-steps of `GraphTraversal` have a `Traversal<E,Vertex>` overload. The `E` has been changed to `?` in order to reduce `< >`-based coersion in strongly type Gremlin language variants.

See: TINKERPOP-1793

#### addV(traversal) and addE(traversal)

The `GraphTraversal` and `GraphTraversalSource` methods of `addV()` and `addE()` have been extended to support dynamic label determination upon element creation. Both these methods can take a `Traversal<?, String>` where the first `String` returned by the traversal is used as the label of the respective element.

    gremlin> g = TinkerFactory.createModern().traversal()
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g.addV(V().has('name','marko').label()).
               property('name','stephen')
    ==>v[13]
    gremlin> g.V().has('name','stephen').valueMap(true)
    ==>[name:[stephen],label:person,id:13]
    gremlin> g.V().has('name','stephen').
               addE(V().hasLabel('software').inE().label()).
                 to(V().has('name','lop'))
    ==>e[15][13-created->3]
    gremlin> g.V().has('name','stephen').outE().valueMap(true)
    ==>[label:created,id:15]
    gremlin>

See: TINKERPOP-1793

#### PageRankVertexProgram

There were two major bugs in the way in which PageRank was being calculated in `PageRankVertexProgram`. First, teleportation energy was not being distributed correctly amongst the vertices at each round. Second, terminal vertices (i.e. vertices with no outgoing edges) did not have their full gathered energy distributed via teleportation.

For users upgrading, note that while the relative rank orders will remain "the same," the actual PageRank values will differ from prior TinkerPop versions.

    VERTEX  iGRAPH    TINKERPOP
    marko   0.1119788 0.11375485828040575
    vadas   0.1370267 0.14598540145985406
    lop     0.2665600 0.30472082661863686
    josh    0.1620746 0.14598540145985406
    ripple  0.2103812 0.1757986539008437
    peter   0.1119788 0.11375485828040575

Normalization preserved through computation:

    0.11375485828040575 +
    0.14598540145985406 +
    0.30472082661863686 +
    0.14598540145985406 +
    0.1757986539008437 +
    0.11375485828040575
    ==>1.00000000000000018

Two other additions to `PageRankVertexProgram` were provided as well.

1. It now calculates the vertex count and thus, no longer requires the user to specify the vertex count.

2. It now allows the user to leverage an epsilon-based convergence instead of having to specify the number of iterations to execute.

See: TINKERPOP-1783

#### IO Defaults

While 3.3.0 released Gryo 3.0 and GraphSON 3.0 and these versions were defaulted in a number of places, it seems that some key defaults were missed. Specifically, calls to `Graph.io(graphson())` and `Graph.io(gryo())` were still using the old versions. The defaults have now been changed to ensure 3.0 is properly referenced in those cases.

#### Upgrade Neo4j

See Neo4j’s 3.2 Upgrade FAQ for a complete guide on how to upgrade from the previous 2.3.3 version. Also note that many of the configuration settings have changed from neo4j 2x to 3x

In particular, these properties referenced in TinkerPop documentation and configuration were renamed:

Neo4j 2.3 (TinkerPop <= 3.3.0) | Neo4j 3.2 (TinkerPop 3.3.1)
--- | ---
node_auto_indexing | dbms.auto_index.nodes.enabled
relationship_auto_indexing | dbms.auto_index.relationships.enabled
ha.cluster_server | ha.host.coordination
ha.server | ha.host.data

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### IO Version Check

In the `Graph.io()` method, providers are to bootstrap the `Io` instance returned with their own custom serializers typically provided through a custom `IoRegistry` instance. Prior to this change it was not possible to easily determine the version of `Io` that was expected (nor was it especially necessary as TinkerPop didn’t have breaking format changes between versions). As of 3.3.0 however, there could be IO test incompatibilities for some providers who need to register a different `IoRegistry` instance depending on the version the user wants.

To allow for that check, the `Io` interface now has the following method:

    public <V> boolean requiresVersion(final V version);

which allows the graph provider to check if a specific `GryoVersion` or `GraphSONVersion` is required. Using that information, the provider could then assign the right `IoRegistry` to match that.

See: TINKERPOP-1767

## TinkerPop 3.3.0

Release Date: August 21, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Packaged Data Files

TinkerPop has always packaged sample graphs with its zip distributions. As of 3.3.0, the distributions will only include Gryo 3.0, GraphSON 3.0 and GraphML (which is unversioned) files. Other versions are not included, but could obviously be generated using the IO API directly.

#### GraphTraversal Has-Methods Re-Organized

`GraphTraversal.hasXXX()`, where `XXX` is `Id`, `Label`, `Key`, `Value`, was faulty in that they relied on calling an intermediate method for flattening `Object[]` arguments and thus, yielding a non 1-to-1 correspondence between `GraphTraversal` and `Bytecode`. This has been remedied. Most users will not notice this change. Perhaps only some users that may use Java reflection over `GraphTraversal` might have a simple problem.

See: TINKERPOP-1520

#### Changes to IO

##### Gryo 3.0

With Gryo, TinkerPop skips version 2.0 and goes right to 3.0 (to maintain better parity with GraphSON versioning). Gryo 3.0 fixes a number of inconsistencies with Gryo 1.0 and hopefully marks a point where Gryo is better versioned over time. Gryo 3.0 is not compatible with Gryo 1.0 and is now the default version of Gryo exposed by TinkerPop in Gremlin Server and IO.

It isn’t hard to switch back to use of Gryo 1.0 if necessary. Here is the approach for writing an entire graph:

    Graph graph = TinkerFactory.createModern();
    GryoMapper mapper = graph.io(IoCore.gryo()).mapper().version(GryoVersion.V1_0).create()
    try (OutputStream os = new FileOutputStream("tinkerpop-modern.json")) {
        graph.io(IoCore.gryo()).writer().mapper(mapper).create().writeGraph(os, graph)
    }

    final Graph newGraph = TinkerGraph.open();
    try (InputStream stream = new FileInputStream("tinkerpop-modern.json")) {
        newGraph.io(IoCore.gryo()).reader().mapper(mapper).create().readGraph(stream, newGraph);
    }

Gremlin Server configurations don’t include Gryo 1.0 by default:

    serializers:
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}             # application/vnd.gremlin-v3.0+gryo
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { serializeResultToString: true }}                                                                       # application/vnd.gremlin-v3.0+gryo-stringd
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GraphSONMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}         # application/json

but adding an entry as follows will add it back:

    serializers:
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV1d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0] }}             # application/vnd.gremlin-v1.0+gryo
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}             # application/vnd.gremlin-v3.0+gryo
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { serializeResultToString: true }}                                                                       # application/vnd.gremlin-v3.0+gryo-stringd
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GraphSONMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}         # application/json

To use Gryo 1.0 with the Java driver, just specify the 1.0 serializer directly:

    GryoMapper.Builder builder = GryoMapper.build().
            version(GryoVersion.V1_0).
            addRegistry(TinkerIoRegistryV1d0.instance());
    Cluster cluster = Cluster.build().serializer(GryoMessageSerializerV1d0(builder));

See: TINKERPOP-1698

##### GraphSON 3.0

GraphSON 3.0 finishes what GraphSON 2.0 began by taking the extra step to include the following types: `g:Map`, `g:List` and `g:Set`. With these types it is now possible to get expected Gremlin results in GLVs just as one would if using Java. This is especially true of the `g:Map` type, which allows non-string keys values, something not allowed in regular JSON maps. This allows for common traversals like `g.V().groupCount()` to work, where the traversal groups on a `Vertex` or some other complex object.

Note that GraphSON 3.0 does not have an option to be without types. This was a feature of 1.0 and 2.0, but it is no longer supported. There is little point to such a feature as we see more movement toward GLVs, which require types, and less usage of scripts with custom parsing of results.

Both TinkerGraph and Gremlin Server have been defaulted to work with GraphSON 3.0. For TinkerGraph this means that the following commands:

    Graph graph = TinkerFactory.createModern();
    graph.io(IoCore.graphson()).writeGraph("tinkerpop-modern.json");

    final Graph newGraph = TinkerGraph.open();
    newGraph.io(IoCore.graphson()).readGraph("tinkerpop-modern.json");

will write and read GraphSON 3.0 format rather than 1.0. To use 1.0 (or 2.0 for that matter) format simply set the `version()` on the appropriate builder methods:

    Graph graph = TinkerFactory.createModern();
    GraphSONMapper mapper = graph.io(IoCore.graphson()).mapper().version(GraphSONVersion.V1_0).create()
    try (OutputStream os = new FileOutputStream("tinkerpop-modern.json")) {
        graph.io(IoCore.graphson()).writer().mapper(mapper).create().writeGraph(os, graph)
    }

    final Graph newGraph = TinkerGraph.open();
    try (InputStream stream = new FileInputStream("tinkerpop-modern.json")) {
        newGraph.io(IoCore.graphson()).reader().mapper(mapper).create().readGraph(stream, newGraph);
    }

For Gremlin Server, this change means that the `application/json` mime type no longer returns GraphSON 1.0 without type embedding. Instead, Gremlin Server will return GraphSON 3.0 with partial types enabled (i.e. which is equivalent to `application/vnd.gremlin-v3.0+json`). The `serializers` section the sample Gremlin Server YAML files now typically look like this:

    serializers:
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}             # application/vnd.gremlin-v3.0+gryo
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { serializeResultToString: true }}                                                                       # application/vnd.gremlin-v3.0+gryo-stringd
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GraphSONMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0] }}         # application/json

It is possible to bring back the original configuration for `application/json` by changing the last entry as follows:

      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV3d0] }}             # application/vnd.gremlin-v3.0+gryo
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { serializeResultToString: true }}                                                                       # application/vnd.gremlin-v3.0+gryo-stringd
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GraphSONMessageSerializerV1d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0]  }}        # application/json

See: TINKERPOP-1414, TINKERPOP-1427, TINKERPOP-1574

#### Graphite and Ganglia

Graphite and Ganglia are no longer packaged with the Gremlin Server distribution. They are considered optional dependencies and therefore must be installed manually by the user.

See: TINKERPOP-1550, Reference Documentation - Metrics

#### SelectStep Defaults to Pop.last

`SelectStep` and `SelectOneStep` (`select()`) are the only `Scoping` steps that default to `Pop.mixed` as their labeled path selection criteria. All other steps, like `match()`, `where()` and `dedup()`, use `Pop.last`. In order to better enable optimizations around total `Pop.last` traversals, the `select()`-steps now default to `Pop.last`. Most users will not notice a difference as it is rare for repeated labels to be used in practice. However, formal backwards compatibility is possible as outlined below.

Assuming that `x` is not a `Pop` argument:

1. Change all `select(x,y,z)` calls to `selectV3d2(x,y,z)` calls.

2. Change all `select(x,y,z)`-step calls to `select(Pop.mixed,x,y,z)`.

If an explicit `Pop` argument is provided, then no changes are required.

See: TINKERPOP-1541

#### OptionalStep and Side-Effects

The `optional()`-step was previously implemented using `ChooseStep`. However, if the optional branch contained side-effects, then unexpected behaviors can emerge. Thus, a potential backwards compatibility issue arises if side-effects were being used in `optional()`. However, the behavior would be unpredictable so this backwards incompatibility is desirable.

See TINKERPOP-1506

#### Gremlin Console Initialization

It is no longer possible to intialize the Gremlin Console with a script without use of `-e`. In other words, prior versions allowed:

    bin/gremlin.sh gremlin.groovy

Such a command must now be written as:

    bin/gremlin.sh -i gremlin.groovy

See: TINKERPOP-1283, TINKERPOP-1651

#### GraphTraversal valueMap() Signature Updated

`GraphTraversal.valueMap(includeTokens,propertyKeys…​)` now returns a `Map<Object,E>` to account for the presence of `T.id` or `T.label` if you pass `true` to it.

See: TINKERPOP-1483

#### HADOOP_GREMLIN_LIBS and Spark

The TinkerPop reference documentation has always mentioned that the `gremlin-spark` `/lib` directory needed to be added to `HADOOP_GREMLIN_LIBS` environment variable. In reality, that was not truly necessary. With Spark 1.x having `gremlin-spark` in `HADOOP_GREMLIN_LIBS` hasn’t been a problem, but Spark 2.0 introduces a check for duplicate jars on the path which will cause job initialization to fail. As a result, going forward with TinkerPop 3.3.0, the `gremlin-spark` `lib` directory should not be included in `HADOOP_GREMLIN_LIBS`.

#### Deprecation Removal

The following deprecated classes, methods or fields have been removed in this version:

- `giraph-gremlin`

  - `org.apache.tinkerpop.gremlin.giraph.groovy.plugin.GiraphGremlinPlugin`

- `gremlin-console`

  - `org.apache.tinkerpop.gremlin.console.Console(String)`

  - `org.apache.tinkerpop.gremlin.console.ConsoleImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.console.plugin.*`

  - `org.apache.tinkerpop.gremlin.console.groovy.plugin.DriverGremlinPlugin`

  - `org.apache.tinkerpop.gremlin.console.groovy.plugin.DriverRemoteAcceptor`

  - `org.apache.tinkerpop.gremlin.console.groovy.plugin.GephiGremlinPlugin`

  - `org.apache.tinkerpop.gremlin.console.groovy.plugin.UtilitiesGremlinPlugin`

- `gremlin-core`

  - `org.apache.tinkerpop.gremlin.jsr223.CoreGremlinModule`

  - `org.apache.tinkerpop.gremlin.jsr223.CoreGremlinPlugin#INSTANCE`

  - `org.apache.tinkerpop.gremlin.jsr223.GremlinModule`

  - `org.apache.tinkerpop.gremlin.jsr223.SingleGremlinScriptEngineManager#getInstance()`

  - `org.apache.tinkerpop.gremlin.jsr223.GremlinScriptEngineManager#addModule(GremlinModule)`

  - `org.apache.tinkerpop.gremlin.jsr223.console.PluginAcceptor`

  - `org.apache.tinkerpop.gremlin.process.traversal.TraversalSource.Builder`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.ConnectiveP(P…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.AndP(P…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.OrP(P…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.TraversalScriptFunction`

  - `org.apache.tinkerpop.gremlin.process.traversal.util.TraversalScriptHelper`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.keyIncr`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.valueIncr`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.keyDecr`

  - `org.apache.tinkerpop.gremlin.process.traversal.Order.valueIncr`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.GraphTraversal.mapKeys()`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.GraphTraversal.mapValues()`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#addV(Object…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#addE(Direction, String, String, Object…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#addOutE(String, String, Object…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#addInV(String, String, Object…​)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#selectV3d2()`

  - `org.apache.tinkerpop.gremlin.process.traversal.Bindings()`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversalSource#withBindings(Bindings)`

  - `org.apache.tinkerpop.gremlin.structure.Transaction.submit(Function)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#sack(BiFunction,String)`

  - `org.apache.tinkerpop.gremlin.process.traversal.strategy.finalization.LazyBarrierStrategy`

  - `org.apache.tinkerpop.gremlin.process.traversal.TraversalSideEffects` (various methods)

  - `org.apache.tinkerpop.gremlin.process.computer.traversal.step.VertexComputing#generateComputer(Graph)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#groupV3d0(String)`

  - `org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal#groupV3d0()`

  - `org.apache.tinkerpop.gremlin.structure.Graph.Features.VertexPropertyFeatures#supportsAddProperty()`

  - `org.apache.tinkerpop.gremlin.structure.Graph.Features.VertexPropertyFeatures#FEATURE_ADD_PROPERTY`

  - `org.apache.tinkerpop.gremlin.structure.Graph.OptIn#SUITE_GROOVY_PROCESS_STANDARD`

  - `org.apache.tinkerpop.gremlin.structure.Graph.OptIn#SUITE_GROOVY_PROCESS_COMPUTER`

  - `org.apache.tinkerpop.gremlin.structure.Graph.OptIn#SUITE_GROOVY_ENVIRONMENT`

  - `org.apache.tinkerpop.gremlin.structure.Graph.OptIn#SUITE_GROOVY_ENVIRONMENT_INTEGRATE`

  - `org.apache.tinkerpop.gremlin.structure.io.Io.Builder#registry(IoRegistry)`

  - `org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONMapper.Builder#embedTypes(boolean)`

  - `org.apache.tinkerpop.gremlin.structure.Transaction.submit(Function)`

  - `org.apache.tinkerpop.gremlin.structure.util.detached.DetachedEdge(Object,String,Map,Pair,Pair)`

  - `org.apache.tinkerpop.gremlin.util.CoreImports`

  - `org.apache.tinkerpop.gremlin.util.ScriptEngineCache`

  - `org.apache.tinkerpop.gremlin.process.computer.util.ConfigurationTraversal`

- `gremlin-driver`

  - `org.apache.tinkerpop.gremlin.driver.Cluster$Builder#reconnectIntialDelay(int)`

  - `org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV1d0(GryoMapper)`

  - `org.apache.tinkerpop.gremlin.driver.ser.AbstractGraphSONMessageSerializerV2d0#TOKEN_USE_MAPPER_FROM_GRAPH`

  - `org.apache.tinkerpop.gremlin.driver.ser.AbstractGryoSONMessageSerializerV2d0#TOKEN_USE_MAPPER_FROM_GRAPH`

- `gremlin-groovy`

  - `org.apache.tinkerpop.gremlin.groovy.AbstractImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.CompilerCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.DefaultImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.EmptyImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.ImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.NoImportCustomizerProvider`

  - `org.apache.tinkerpop.gremlin.groovy.engine.ConcurrentBindings`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor#build(String,List,List,List,Map)`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor#getScriptEngines()`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor#getGlobalBindings()`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.Builder#enabledPlugins(Set)`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.Builder#addEngineSettings(String,List,List,List,Map)`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.Builder#engineSettings(Map)`

  - `org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.Builder#use(List)`

  - `org.apache.tinkerpop.gremlin.groovy.engine.ScriptEngines`

  - `org.apache.tinkerpop.gremlin.groovy.function.*`

  - `org.apache.tinkerpop.gremlin.groovy.plugin.*`

  - `org.apache.tinkerpop.gremlin.groovy.plugin.credential.*`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.DependencyManager`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine(ImportCustomizerProvider)`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine(CompilerCustomizerProvider)`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine#plugins()`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.ScriptExecutor`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.ScriptEnginePluginAcceptor`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.customizer.SandboxExtension`

  - `org.apache.tinkerpop.gremlin.groovy.jsr223.customizer.*`

  - `org.apache.tinkerpop.gremlin.groovy.util.DependencyGrabber#deleteDependenciesFromPath(org.apache.tinkerpop.gremlin.groovy.plugin.Artifact)`

  - `org.apache.tinkerpop.gremlin.groovy.util.DependencyGrabber#copyDependenciesToPath(org.apache.tinkerpop.gremlin.groovy.plugin.Artifact)`

- `gremlin-python`

  - `org.apache.tinkerpop.gremlin.python.jsr223.GremlinJythonScriptEngine#()`

- `gremlin-server`

  - `org.apache.tinkerpop.gremlin.server.GremlinServer(ServerGremlinExecutor)`

  - `org.apache.tinkerpop.gremlin.server.Settings#plugins`

  - `org.apache.tinkerpop.gremlin.server.auth.AllowAllAuthenticator.newSaslNegotiator()`

  - `org.apache.tinkerpop.gremlin.server.auth.Authenticator.newSaslNegotiator()`

  - `org.apache.tinkerpop.gremlin.server.auth.Krb5Authenticator.newSaslNegotiator()`

  - `org.apache.tinkerpop.gremlin.server.auth.SimpleAuthenticator.newSaslNegotiator()`

  - `org.apache.tinkerpop.gremlin.server.handler.IteratorHandler`

  - `org.apache.tinkerpop.gremlin.server.handler.NioGremlinResponseEncoder`

  - `org.apache.tinkerpop.gremlin.server.handler.WsGremlinResponseEncoder`

  - `org.apache.tinkerpop.gremlin.server.handler.OpSelectorHandler.errorMeter`

  - `org.apache.tinkerpop.gremlin.server.op.control.*`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractEvalOpProcessor.errorMeter`

  - `org.apache.tinkerpop.gremlin.server.op.AbstractEvalOpProcessor.validBindingName`

  - `org.apache.tinkerpop.gremlin.server.op.session.Session.kill()`

  - `org.apache.tinkerpop.gremlin.server.op.session.Session.manualkill()`

- `hadoop-gremlin`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_HADOOP_GRAPH_INPUT_FORMAT`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_HADOOP_GRAPH_OUTPUT_FORMAT`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_HADOOP_GRAPH_INPUT_FORMAT_HAS_EDGES`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_HADOOP_GRAPH_OUTPUT_FORMAT_HAS_EDGES`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_SPARK_GRAPH_INPUT_RDD`

  - `org.apache.tinkerpop.gremlin.hadoop.Constants#GREMLIN_SPARK_GRAPH_OUTPUT_RDD`

- `spark-gremlin`

  - `org.apache.tinkerpop.gremlin.spark.groovy.plugin.SparkGremlinPlugin`

- `tinkergraph-gremlin`

  - `org.apache.tinkerpop.gremlin.tinkergraph.groovy.plugin.TinkerGraphGremlinPlugin`

  - `org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerGraph#CONFIG_*`

  - `org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistry`

  - `org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0#getInstance()`

  - `org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV2d0#getInstance()`

Please see the javadoc deprecation notes or upgrade documentation specific to when the deprecation took place to understand how to resolve this breaking change.

See: TINKERPOP-832, TINKERPOP-833, TINKERPOP-834, TINKERPOP-999, TINKERPOP-1010, TINKERPOP-1028, TINKERPOP-1040, TINKERPOP-1046, TINKERPOP-1049, TINKERPOP-1142, TINKERPOP-1169, TINKERPOP-1171, TINKERPOP-1275, TINKERPOP-1283, TINKERPOP-1289, TINKERPOP-1291, TINKERPOP-1420, TINKERPOP-1421, TINKERPOP-1465, TINKERPOP-1481, TINKERPOP-1526, TINKERPOP-1603, TINKERPOP-1612, TINKERPOP-1622, TINKERPOP-1651, TINKERPOP-1694, TINKERPOP-1700, TINKERPOP-1706, TINKERPOP-1721, TINKERPOP-1719, TINKERPOP-1720, TINKERPOP-880, TINKERPOP-1170, TINKERPOP-1729

#### Gremlin-server.sh and Init Scripts

`gremlin-server.sh` is now also an init script and can no longer be started without parameters. To start it in the foreground with defaults like previous usage, please use the `console` parameter. Also, `gremlin-server.sh` will continue to start in the foreground when provided a yaml configuration file.

How to install as a service has been added to the Reference Documentation - As A Service.

The switch name has changed for installing dependencies. `-i` has been deprecated and replaced by `install`.

See: TINKERPOP-980, Reference Documentation - Server Configuration.

#### Removal of useMapperFromGraph

The `userMapperFromGraph` serialization configuration option was used to allow the IO configurations of a specific graph to be assigned to a specific serializer. This feature has been removed completely now. Please use the `ioRegistries` configuration option to add one or more specific `Graph` serialization capabilities to a serializer.

    serializers:
      - { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV1d0, config: { ioRegistries: [org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerIoRegistryV1d0] }}            # application/vnd.gremlin-v1.0+gryo

see: TINKERPOP-1699

#### Gremlin-server.bat

The switch name has changed for installing dependencies. `-i` has been deprecated and replaced by `install`.

#### SparkGraphComputer GryoRegistrator

Historically, `SparkGraphComputer` has used `GryoSerializer` to handle the serialization of objects in Spark. The reason this exists is because TinkerPop uses a shaded version of Kryo and thus, couldn’t use the standard `KryoSerializer`-model provided by Spark. However, a "shim model" was created which allows for the shaded and unshaded versions of Kryo to interact with one another. To this end, `KryoSerializer` can now be used with a `GryoRegistrator`. The properties file for a `SparkGraphComputer` now looks as follows:

    spark.serializer=org.apache.spark.serializer.KryoSerializer
    spark.kryo.registrator=org.apache.tinkerpop.gremlin.spark.structure.io.gryo.GryoRegistrator

If the old `GryoSerializer` model is desired, then the properties file should simply look as before:

    spark.serializer=org.apache.tinkerpop.gremlin.spark.structure.io.gryo.GryoSerializer

See: TINKERPOP-1389

#### ScriptInputFormat

The API for the script provided to a `ScriptInputFormat` has changed slightly. The signature for `parse(line, factory)` is now simply `parse(line)`. The inclusion of `factory` was deprecated in 3.1.2. Instead of using the {{factory}} to get the {{StarGraph}} there is a {{graph}} variable in the glocal context of the script. Simply use that directly in the script.

See: TINKERPOP-1137, Reference Documentation - Script I/O Format

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### GremlinPlugin

The previously deprecated `GremlinPlugin` system has been removed. The old `GremlinPlugin` interface formerly resided in the `org.apache.tinkerpop.gremlin.groovy.plugin` package of `gremlin-groovy`. This interface was replaced by an interface of the same name in 3.2.4, which now resides in the `org.apache.tinkerpop.gremlin.jsr223` package in `gremlin-core`. Obviously, existing plugins will need to be updated to use this new interface.

The plugin model has changed slightly to be more generic and not specifically bound to Groovy based script engines. Under the new model, the plugin simply returns `Customizer` instances that can be applied generically to any `ScriptEngine` or specifically to a particular `ScriptEngine`. More details can be found in the Provider Documentation

#### Graph Database Providers

##### Test Suite Removal

A number of test suites that were previously deprecated have been removed which should reduce the burden on graph providers who are implementing TinkerPop. Test suites related to perfrmance based on `junit-benchmarks` have been removed as have the suites in `gremlin-groovy-test` (in fact, this entire module has been removed). Specifically, providers should be concerned with breaking changes related to the removal of:

- `StructurePerformanceSuite`

- `ProcessPerformanceSuite`

- `GroovyEnvironmentPerformanceSuite`

- `GroovyProcessStandardSuite`

- `GroovyProcessComputerSuite`

- `GroovyEnvironmentSuite`

- `GroovyEnvironmentIntegrateSuite`

Those graph providers who relied on these tests should simply remove them from their respective test suites. Beware of `OptOut` annotations that reference tests in these suites as test failure will occur if those references are not removed.

See: TINKERPOP-1235, TINKERPOP-1612

##### TransactionException

The `AbstractTransaction.TransactionException` class is now just `TransactionException` which extends `RuntimeExcetpion` rather than `Exception`. Providers should consider using this exception to wrap their own on calls to `Transaction.commit()` or `Transaction.rollback()`. By throwing this exception, the TinkerPop stack can better respond to transaction problems and it allows for more common, generalized error handling for users.

See: TINKERPOP-1004

#### Driver Providers

##### SASL Byte Array

Gremlin Server no longer supports accepting a byte array for the value passed to the "sasl" parameter in authentication messages. It only accepts a Base64 encoded string.

See: TINKERPOP-1603

# TinkerPop 3.2.0

Nine Inch Gremlins

## TinkerPop 3.2.11

Release Date: January 2, 2019

Please see the changelog for a complete list of all the modifications that are part of this release.

## TinkerPop 3.2.10

Release Date: October 15, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### SASL in Gremlin-Javascript

The Gremlin Javascript Driver now supports SASL Plain Text authentication against a Gremlin Server.

See: TINKERPOP-1977, Reference Documentation - Gremlin Javascript

#### SSL Security

TinkerPop improves its security posture by removing insecure defaults and adding forward-looking standards support.

Gremlin Server no longer supports automatically creating self-signed certificates. Self-signed certificates can still be created manually outside of Gremlin Server. If ssl is enabled, a key store must be configured.

Cluster client no longer trusts all certs by default as this is an insecure configuration. Instead, if no trust store is configured, Cluster will use the default CA certs. To revert to the previous behavior and accept all certs, it must be explicitly configured.

This release introduces JKS and PKCS12 support. JKS is the legacy Java Key Store. PKCS12 has better cross-platform support and is gaining in adoption. Be aware that JKS is the default on Java 8. Java 9 and higher use PKCS12 as the default. Both Java keytool and OpenSSL tools can create, read, update PKCS12 files.

Other new features include specifying SSL protocols and cipher suites. The packaged `*-secure.yaml` files now restrict the protocol to `TLSv1.2` by default.

PEM-based configurations are deprecated and may be removed in a future release.

See also Connecting via Java Configuration, Gremlin Server Configuration.

TINKERPOP-2022 TINKERPOP-2023

#### Bulk Import and Export

TinkerPop has provided some general methods for importing and exporting data, but more and more graph providers are producing their own bulk import/export facilities and they are more efficient and easier to use than TinkerPop’s methods. As a result, TinkerPop will now refer users to the bulk import/export features of individual graph providers and as such, has deprecated `BulkLoaderVertexProgram` as of this release.

As part of this change, the `BulkDumperVertexProgram` has been renamed to `CloneVertexProgram` with the former being deprecated. `CloneVertexProgram` is more aptly named, as it essentially copies a graph from a graph `InputFormat` to a graph `OutputFormat`.

TINKERPOP-1985

#### Docker Images

Docker images are now available on Docker Hub for Gremlin Console and Gremlin Server.

    $ docker run -it tinkerpop/gremlin-console:3.5.1
    $ docker run tinkerpop/gremlin-server:3.5.1

See: TINKERPOP-1897, Reference Documentation - Gremlin Console, Reference Documentation - Gremlin Server,

#### TimedInterruptCustomizerProvider

In Gremlin Server, it is best not to use 'TimedInterruptCustomizerProvider' because it can compete with the 'scriptEvaluationTimeout' setting and produce a different error path. Simply rely on 'scriptEvaluationTimeout' as it covers both script evaluation time and result iteration time.

See: TINKERPOP-1778

#### TinkerFactory.createGratefulDead()

The Grateful Dead dataset has been with TinkerPop since the early days of 1.x. It has always been available as a packaged dataset that needed to be loaded through the various IO options available, while other toy graphs had the benefit of `TinkerFactory` to help get them bootstrapped. For 3.2.10, Grateful Dead is now more conveniently loaded via that same method as the other toy graphs with `TinkerFactory.createGratefulDead()`.

#### Gremlin Javascript Script Submission

Gremlin Javascript can now submit script, with optional bindings, using the `Client` class:

    const gremlin = require('gremlin');
    const client = new gremlin.driver.Client('ws://localhost:8182/gremlin', { traversalSource: 'g' });

    client.submit('g.V().tail()')
        .then(result => {
            console.log(result.length);
            console.log(result.toArray()[0]);
        });

    client.submit('g.V(vid)', { vid: 1 })
        .then(result => {
            console.log(result.length);
            // Get the first item
            console.log(result.first());
        });

and also allows translation of bytecode steps into script:

    const gremlin = require('gremlin');
    const graph = new gremlin.process.Graph();
    const client = new gremlin.driver.Client('ws://localhost:8182/gremlin', { traversalSource: 'g' });
    const translator = new gremlin.process.Translator('g');

    const g = graph.traversal();
    const script = translator.translate(g.V().tail().getBytecode());

    client.submit(script)
        .then(result => {
            console.log(result.length);
            console.log(result.first());
        });

### Upgrading for Providers

#### Graph Database Providers

##### Bulk Import and Export

As noted in the user section, TinkerPop has deprecated its bulk loading feature in `BulkLoaderVertexProgram` and will refer TinkerPop users who need bulk import/export capabilities to the native tools of the graph database they have chosen. If a graph database provider does not have any bulk loading tools it can choose to build graph `InputFormat` and `OutputFormat` implementations which can be used by `CloneVertexProgram` (formerly `BulkDumperVertexProgram`) as a easy way to get such a feature.

TINKERPOP-1985

## TinkerPop 3.2.9

Release Date: May 8, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Lambda Construction

It was realized quite shortly after release of 3.2.8 that there was a bug in construction of `Lambda` instances:

    gremlin> org.apache.tinkerpop.gremlin.util.function.Lambda.function("{ it.get() }")
    (class: org/apache/tinkerpop/gremlin/util/function/Lambda$function, method: callStatic signature: (Ljava/lang/Class;[Ljava/lang/Object;)Ljava/lang/Object;) Illegal type in constant pool
    Type ':help' or ':h' for help.
    Display stack trace? [yN]n

The problem was related to a bug in Groovy 2.4.14 and was fixed in 2.4.15.

See: TINKERPOP-1953

## TinkerPop 3.2.8

Release Date: April 2, 2018

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Improved Connection Monitoring

Gremlin Server now has two new settings: `idleConnectionTimeout` and `keepAliveInterval`. The `keepAliveInterval` tells Gremlin Server how long it should wait between writes to a client before it issues a "ping" to that client to see if it is still present. The `idleConnectionTimeout` represents how long Gremlin Server should wait between requests from a client before it closes the connection on the server side. By default, these two configurations are set to zero, meaning that they are both disabled.

This change should help to alleviate issues where connections are left open on the server longer than they should be by clients that might mysteriously disappear without properly closing their connections.

See: TINKERPOP-1726

#### Gremlin.Net Lambdas

Gremlin.Net now has a `Lambda` class that can be used to construct Groovy or Java lambdas which will be evaluated on the server.

See: TINKERPOP-1854, Reference Documentation - Gremlin.Net - The Lambda Solution.

#### Gremlin.Net Tokens Improved

The various Gremlin tokens (e.g. `T`, `Order`, `Operator`, etc.) that were implemented as Enums before in Gremlin.Net are now implemented as classes. This mainly allows them to implement interfaces which their Java counterparts already did. `T` for example now implements the new interface `IFunction` which simply mirrors its Java counterpart `Function`. Steps that expect objects for those interfaces as arguments now explicitly use the interface. Before, they used just `object` as the type for these arguments which made it hard for users to know what kind of `object` they can use. However, usage of these tokens themselves shouldn’t change at all (e.g. `T.Id` is still `T.Id`).

See: TINKERPOP-1901

#### Gremlin.Net: Traversal Predicate Classes Merged

Gremlin.Net used two classes for traversal predicates: `P` and `TraversalPredicate`. Steps that worked with traversal predicates expected objects of type `TraversalPredicate`, but they were constructed from the `P` class (e.g. `P.Gt(1)` returned a `TraversalPredicate`). Merging these two classes into the `P` class should avoid unnecessary confusion. Most users should not notice this change as predicates can still be constructed exactly as before, e.g., `P.Gt(1).And(P.Lt(3))` still works without any modifications. Only users that implemented their own predicates and used `TraversalPredicate` as the base class need to change their implementation to now use `P` as the new base class.

See: TINKERPOP-1919

### Upgrading for Providers

#### Graph System Providers

##### Kitchen Sink Test Graph

The "Kitchen Sink" test graph has been added to the `gremlin-test` module. It contains (or will contain) various disconnected subgraphs of that offer unique structures (e.g. a self-loop) for specific test cases. Graph systems that use the test suite should not have to make any changes to account for this new graph unless that system performs some form or special pre-initialization of their system in preparation for loading (e.g. requires a schema) or does the loading of the graph test data outside of the standard method in which TinkerPop provides.

See: TINKERPOP-1877

## TinkerPop 3.2.7

Release Date: December 17, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin-Python Core Types

With the addition of `UUID`, `Date`, and `Timestamp`, Gremlin-Python now implements serializers for all core GraphSON types. Users that were using other types to represent this data can now use the Python classes `datetime.datetime` and`uuid.UUID` in GLV traversals. Since Python does not support a native `Timestamp` object, Gremlin-Python now offers a dummy class `Timestamp`, which allows users to wrap a float and submit it to the Gremlin Server as a `Timestamp` GraphSON type. `Timestamp` can be found in `gremlin_python.statics`.

See: TINKERPOP-1807

#### EventStrategy Detachment

`EventStrategy` forced detachment of mutated elements prior to raising them in events. While this was a desired outcome, it may not have always fit every use case. For example, a user may have wanted a reference element or the actual element itself. As a result, `EventStrategy` has changed to allow it to be constructed with a `detach()` option, where it is possible to specify any of the following: `null` for no detachment, `DetachedFactory` for the original behavior, and `ReferenceFactory` for detachment that returns reference elements.

See: TINKERPOP-1829

#### Embedded Remote Connection

As Gremlin Language Variants (GLVs) expand their usage and use of `withRemote()` becomes more common, the need to mock the "remote" in unit tests increases. To simplify mocking in Java, the new `EmbeddedRemoteConnection` provides a simple way to provide a "remote" that is actually local to the same JVM.

See: TINKERPOP-1756

#### DSL Type Specification

Prior to this version, the Java annotation processor for Gremlin DSLs has tried to infer the appropriate type specifications when generating anonymous methods. It largely performed this inference on simple conventions in the DSL method’s template specification and there were times where it would fail. For example, a method like this:

    public default GraphTraversal<S, E> person() {
        return hasLabel("person");
    }

would generate an anonymous method like:

    public static <S> SocialGraphTraversal<S, E> person() {
        return hasLabel("person");
    }

and, of course, generate a compile error and `E` was not recognized as a symbol. The preferred generation would likely be:

    public static <S> SocialGraphTraversal<S, S> person() {
        return hasLabel("person");
    }

To remedy this situation, a new annotation has been added which allows the user to control the type specifications more directly providing a way to avoid/override the inference system:

    @GremlinDsl.AnonymousMethod(returnTypeParameters = {"A", "A"}, methodTypeParameters = {"A"})
    public default GraphTraversal<S, E> person() {
        return hasLabel("person");
    }

which will then generate:

    public static <A> SocialGraphTraversal<A, A> person() {
        return hasLabel("person");
    }

See: TINKERPOP-1791

#### Specify a Cluster Object

The `:remote connect` command can now take a pre-defined `Cluster` object as its argument as opposed to a YAML configuration file.

    gremlin> cluster = Cluster.open()
    ==>localhost/127.0.0.1:8182
    gremlin> :remote connect tinkerpop.server cluster
    ==>Configured localhost/127.0.0.1:8182

See: TINKERPOP-1787

#### Remote Traversal Timeout

There was limited support for "timeouts" with remote traversals (i.e. those traversals executed using the `withRemote()` option) prior to 3.2.7. Remote traversals will now interrupt on the server using the `scriptEvaluationTimeout` setting in the same way that normal script evaluations would. As a reminder, interruptions for traversals are always considered "attempts to interrupt" and may not always succeed (a graph database implementation might not respect the interruption, for example).

See: TINKERPOP-1770

#### Modifications to match()

The `match()`-step has been generalized to support the local scoping of all barrier steps, not just reducing barrier steps. Previously, the `order().limit()` clause would have worked globally yielding:

    gremlin> g.V().match(
    ......1>   __.as('a').outE('created').order().by('weight',decr).limit(1).inV().as('b'),
    ......2>   __.as('b').has('lang','java')
    ......3> ).select('a','b').by('name')
    ==>[a:marko,b:lop]

However, now, `order()` (and all other barriers) are treated as local computations to the pattern and thus, the result set is:

    gremlin> g.V().match(
    ......1>   __.as('a').outE('created').order().by('weight',decr).limit(1).inV().as('b'),
    ......2>   __.as('b').has('lang','java')
    ......3> ).select('a','b').by('name')
    ==>[a:marko,b:lop]
    ==>[a:josh,b:ripple]
    ==>[a:peter,b:lop]

Note that this is not that intense of a breaking change as all of the reducing barriers behaved in this manner previously. This includes steps like `count()`, `min()`, `max()`, `sum()`, `group()`, `groupCount()`, etc. This update has now generalized this behavior to all barriers and thus, adds `aggregate()`, `dedup()`, `range()`, `limit()`, `tail()`, and `order()` to the list of locally computed clauses.

See: TINKERPOP-1764

#### Clone a Graph

In `gremlin-test` there is a new `GraphHelper` class that has a `cloneElements()` method. It will clone elements from the first graph to the second - `GraphHelper.cloneElements(Graph original, Graph clone)`. This helper method is primarily intended for use in tests.

#### MutationListener Changes

The `MutationListener` has a method called `vertexPropertyChanged` which gathered callbacks when a property on a vertex was modified. The method had an incorrect signature though using `Property` instead of `VertexProperty`. The old method that used `Property` has now been deprecated and a new method added that uses `VertexProperty`. This new method has a default implementation that calls the old method, so this change should not cause breaks in compilation on upgrade. Internally, TinkerPop no longer calls the old method except by way of that proxy. Users who have `MutationListener` implementations can simply add the new method and override its behavior. The old method can thus be ignored completely.

See: TINKERPOP-1798

### Upgrading for Providers

#### Direction.BOTH Requires Duplication of Self-Edges

Prior to this release, there was no semantic check to determine whether a self-edge (e.g. `e[1][2-self→2]`) would be returned twice on a `BOTH`. The semantics have been specified now in the test suite where the edge should be returned twice as it is both an incoming edge and an outgoing edge.

See: TINKERPOP-1821

## TinkerPop 3.2.6

Release Date: August 21, 2017

### Upgrading for Users

Please see the changelog for a complete list of all the modifications that are part of this release.

#### Deprecated useMapperFromGraph

The `userMapperFromGraph` configuration option for the Gremlin Server serializers has been deprecated. Change configuration files to use the `ioRegistries` option instead. The `ioRegistries` option is not a new feature, but it has not been promoted as the primary way to add `IoRegistry` instances to serializers.

See: TINKERPOP-1694

#### WsAndHttpChannelizer

The `WsAndHttpChannelizer` has been added to allow for processing both WebSocket and HTTP requests on the same port and gremlin server. The `SaslAndHttpBasicAuthenticationHandler` has also been added to service authentication for both protocols in conjunction with the `SimpleAuthenticator`.

See: TINKERPOP-915

### Upgrading for Providers

#### ReferenceVertex Label

`ReferenceVertex.label()` was hard coded to return `EMPTY_STRING`. At some point, `ReferenceElements` were suppose to return labels and `ReferenceVertex` was never updated as such. Note that `ReferenceEdge` and `ReferenceVertexProperty` work as expected. However, given a general change at `ReferenceElement`, the Gryo serialization of `ReferenceXXX` is different. If the vertex does not have a label `Vertex.DEFAULT_LABEL` is assumed.

See: TINKERPOP-1789

## TinkerPop 3.2.5

Release Date: June 12, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### DSL Support

It has always been possible to construct Domain Specific Languages (DSLs) with Gremlin, but the approach has required a somewhat deep understanding of the TinkerPop code base and it is not something that has had a recommended method for implementation. With this release, TinkerPop simplifies DSL development and provides the best practices for their implementation.

    // standard Gremlin
    g.V().hasLabel('person').
      where(outE("created").count().is(P.gte(2))).count()

    // the same traversal as above written as a DSL
    social.persons().where(createdAtLeast(2)).count()

See: TINKERPOP-786, Reference Documentation

#### GraphSON Path Serialization

Serialization of `Path` with GraphSON was inconsistent with Gryo in that all the properties on any elements of the `Path` were being included. With Gryo that, correctly, was not happening as that could be extraordinarily expensive. GraphSON serialization has now been modified to properly not include properties. That change can cause breaks in application code if that application code tries to access properties on elements in a `Path` as they will no longer be there. Applications that require the properties will need to alter their Gremlin to better restrict the data they want to retrieve.

See: TINKERPOP-1676

#### Authentication Configuration

The server settings previously used `authentication.className` to set an authenticator for the the two provided authentication handler and channelizer classes to use. This has been deprecated in favor of `authentication.authenticator`. A class that extends `AbstractAuthenticationHandler` may also now be provided as `authentication.authenticationHandler` to be used in either of the provided channelizer classes to handle the provided authenticator

See: TINKERPOP-1657

#### Default Maximum Parameters

It was learned that compilation for scripts with large numbers of parameters is more expensive than those with less parameters. It therefore becomes possible to make some mistakes with how Gremlin Server is used. A new setting on the `StandardOpProcessor` and `SessionOpProcessor` called `maxParameters` controls the number of parameters that can be passed in on a request. This setting is defaulted to sixteen.

Users upgrading to this version may notice errors in their applications if they use more than sixteen parameters. To fix this problem simply reconfigure Gremlin Server with a configuration as follows:

    processors:
      - { className: org.apache.tinkerpop.gremlin.server.op.session.SessionOpProcessor, config: { maxParameters: 64 }}
      - { className: org.apache.tinkerpop.gremlin.server.op.standard.StandardOpProcessor, config: { maxParameters: 64 }}

The above configuration allows sixty-four parameters to be passed on each request.

See: TINKERPOP-1663

#### GremlinScriptEngine Metrics

The `GremlinScriptEngine` has a number of new metrics about its cache size and script compilation times which should be helpful in understanding usage problems. As `GremlinScriptEngine` instances are used in Gremlin Server these metrics are naturally exposed as part of the standard metrics set. Note that metrics are captured for both sessionless requests as well as for each individual session that is opened.

See: TINKERPOP-1644

#### Additional Error Information

Additional information on error responses from Gremlin Server should help make debugging errors easier. Error responses now have both the exception hierarchy and the stack trace that was generated on the server. In this way, receiving an error on a client doesn’t mean having to rifle through Gremlin Server logs to try to find the associated error.

This change has been applied to all Gremlin Server protocols. For the binary protocol and the Java driver this change means that the `ResponseException` thrown from calls to `submit()` requests to the server now have the following methods:

    public Optional<String> getRemoteStackTrace()

    public Optional<List<String>> getRemoteExceptionHierarchy()

The HTTP protocol has also been updated and returns both `exceptions` and `stackTrace` fields in the response:

    {
            "message": "Division by zero",
            "Exception-Class": "java.lang.ArithmeticException",
            "exceptions": ["java.lang.ArithmeticException"],
            "stackTrace": "java.lang.ArithmeticException: Division by zero\n\tat java.math.BigDecimal.divide(BigDecimal.java:1742)\n\tat org.codehaus.groovy.runtime.typehandling.BigDecimalMath.divideImpl(BigDecimalMath.java:68)\n\tat org.codehaus.groovy.runtime.typehandling.IntegerMath.divideImpl(IntegerMath.java:49)\n\tat org.codehaus.groovy.runtime.dgmimpl.NumberNumberDiv$NumberNumber.invoke(NumberNumberDiv.java:323)\n\tat org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)\n\tat org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)\n\tat org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)\n\tat org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)\n\tat Script4.run(Script4.groovy:1)\n\tat org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine.eval(GremlinGroovyScriptEngine.java:834)\n\tat org.apache.tinkerpop.gremlin.groovy.jsr223.GremlinGroovyScriptEngine.eval(GremlinGroovyScriptEngine.java:547)\n\tat javax.script.AbstractScriptEngine.eval(AbstractScriptEngine.java:233)\n\tat org.apache.tinkerpop.gremlin.groovy.engine.ScriptEngines.eval(ScriptEngines.java:120)\n\tat org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.lambda$eval$2(GremlinExecutor.java:314)\n\tat java.util.concurrent.FutureTask.run(FutureTask.java:266)\n\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)\n\tat java.lang.Thread.run(Thread.java:745)\n"
    }

Note that the `Exception-Class` which was added in a previous version has been deprecated and replaced by these new fields.

See: TINKERPOP-1044

#### Gremlin Console Scripting

The `gremlin.sh` command has two flags, `-i` and `-e`, which are used to pass a script and arguments into the Gremlin Console for execution. Those flags now allow for passing multiple scripts and related arguments to be supplied which can yield greater flexibility in automation tasks.

    $ bin/gremlin.sh -i y.groovy 1 2 3 -i x.groovy
    $ bin/gremlin.sh -e y.groovy 1 2 3 -e x.groovy

See: TINKERPOP-1653

#### Path support for by()-, from()-, to()-modulation

It is now possible to extract analyze sub-paths using `from()` and `to()` modulations with respective, path-based steps. Likewise, `simplePath()` and `cyclicPath()` now support, along with `from()` and `to()`, `by()`-modulation so the cyclicity is determined by projections of the path data. This extension is fully backwards compatible.

See: TINKERPOP-1387

#### GraphManager versus DefaultGraphManager

Gremlin Server previously implemented its own final `GraphManager` class. Now, the `GraphManager` has been changed to an interface, and users can supply their own `GraphManager` implementations in their YAML. The previous `GraphManager` class was meant be used by classes internal to Gremlin Server, but it was public so if it was used for some reason by users then then a compile error can be expected. To correct this problem, which will likely manifest as a compile error when trying to create a `new GraphManager()` instance, simply change the code to `new DefaultGraphManager(Settings)`.

In addition to the change mentioned above, several methods on `GraphManager` were deprecated:

- `getGraphs()` should be replaced by the combination of `getGraphNames()` and then `getGraph(String)`

- `getTraversalSources()` is similarly replaced and should instead use a combination of `getTraversalSourceNames()` and `getTraversalSource(String)`

See: TINKERPOP-1438

#### Gremlin-Python Driver

Gremlin-Python now offers a more complete driver implementation that uses connection pooling and the Python `concurrent.futures` module to provide asynchronous I/0 using threading. The default underlying WebSocket client implementation is still provided by Tornado, but it is trivial to plug in another client by defining the `Transport` interface.

Using the `DriverRemoteConnection` class is the exact same as in previous versions; however, `DriverRemoteConnection` now uses the new `Client` class to submit messages to the server.

The `Client` class implementation/interface is based on the Java Driver, with some restrictions. Most notably, Gremlin-Python does not yet implement the `Cluster` class. Instead, `Client` is instantiated directly. Usage is as follows:

    from gremlin_python.driver import client

    client = client.Client('ws://localhost:8182/gremlin', 'g')
    result_set = client.submit('1 + 1')
    future_results = result_set.all()  # returns a concurrent.futures.Future
    results = future_results.result()  # returns a list
    assert results == [2]
    client.close()  # don't forget to close underlying connections

See: TINKERPOP-1599

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### SimplePathStep and CyclicPathStep now PathFilterStep

The Gremlin traversal machine use to support two step instructions: `SimplePathStep` and `CyclicPathStep`. These have been replaced by a high-level instruction called `PathFilterStep` which is boolean configured for simple or cyclic paths. Furthermore, `PathFilterStep` also support `from()`-, `to()`-, and `by()`-modulation.

##### LazyBarrierStrategy No Longer End Appends Barriers

`LazyBarrierStrategy` was trying to do to much by considering `Traverser` effects on network I/O by appending an `NoOpBarrierStrategy` to the end of the root traversal. This should not be accomplished by `LazyBarrierStrategy`, but instead by `RemoteStrategy`. `RemoteStrategy` now tries to barrier-append. This may effect the reasoning logic in some `ProviderStrategies`. Most likely not, but just be aware.

See: TINKERPOP-1627

## TinkerPop 3.2.4

Release Date: February 8, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### TinkerGraph Deserialization

A TinkerGraph deserialized from Gryo or GraphSON is now configured with multi-properties enabled. This change allows TinkerGraphs returned from Gremlin Server to properly return multi-properties, which was a problem seen when subgraphing a graph that contained properties with a setting other than `Cardinality.single`.

This change could be considered breaking in the odd chance that a TinkerGraph returned from Gremlin Server was later mutated, because calls to `property(k,v)` would default to `Cardinality.list` instead of `Cardinality.single`. In the event that this is a problem, simple change calls to `property(k,v)` to `property(Cardinality.single,k,v)` and explicitly set the `Cardinality`.

See: TINKERPOP-1587

#### Traversal Promises

The `Traversal` API now has a new `promise()` method. These methods return a promise in the form of a `CompleteableFuture`. Usage is as follows:

    gremlin> promise = g.V().out().promise{it.next()}
    ==>java.util.concurrent.CompletableFuture@4aa3d36[Completed normally]
    gremlin> promise.join()
    ==>v[3]
    gremlin> promise.isDone()
    ==>true
    gremlin> g.V().out().promise{it.toList()}.thenApply{it.size()}.get()
    ==>6

At this time, this method is only used for traversals that are configured using `withRemote()`.

See: TINKERPOP-1490

#### If/Then-Semantics with Choose Step

Gremlin’s `choose()`-step supports if/then/else-semantics. Thus, to effect if/then-semantics, `identity()` was required. Thus, the following two traversals below are equivalent with the later being possible in this release.

    g.V().choose(hasLabel('person'),out('created'),identity())
    g.V().choose(hasLabel('person'),out('created'))

See: TINKERPOP-1508

#### FastNoSuchElementException converted to regular NoSuchElementException

Previously, a call to `Traversal.next()` that did not have a result would throw a `FastNoSuchElementException`. This has been changed to a regular `NoSuchElementException` that includes the stack trace. Code that explicitly catches `FastNoSuchElementException` should be converted to check for the more general class of `NoSuchElementException`.

See: TINKERPOP-1330

#### ScriptEngine support in gremlin-core

`ScriptEngine` and `GremlinPlugin` infrastructure has been moved from gremlin-groovy to gremlin-core to allow for better re-use across different Gremlin Language Variants. At this point, this change is non-breaking as it was implemented through deprecation.

The basic concept of a `ScriptEngine` has been replaced by the notion of a `GremlinScriptEngine` (i.e. a "ScriptEngine" that is specifically tuned for executing Gremlin-related scripts). "ScriptEngine" infrastructure has been developed to help support this new interface, specifically `GremlinScriptEngineFactory` and `GremlinScriptEngineManager`. Prefer use of this infrastructure when instantiating a `GremlinScriptEngine` rather than trying to instantiate directly.

For example, rather than instantiate a `GremlinGroovyScriptEngine` with the constructor:

    GremlinScriptEngine engine = new GremlinGroovyScriptEngine();

prefer to instantiate it as follows:

    GremlinScriptEngineManager manager = new CachedGremlinScriptEngineManager();
    GremlinScriptEngine engine = manager.getEngineByName("gremlin-groovy");

Related to the addition of `GremlinScriptEngine`, `org.apache.tinkerpop.gremlin.groovy.plugin.GremlinPlugin` in gremlin-groovy has been deprecated and then replaced by `org.apache.tinkerpop.gremlin.jsr223.GremlinPlugin`. The new version of `GremlinPlugin` is similar but does carry some new methods to implement that involves the new `Customizer` interface. The `Customizer` interface is the way in which `GremlinScriptEngine` instance can be configured with imports, initialization scripts, compiler options, etc.

Note that a `GremlinPlugin` can be applied to a `GremlinScriptEngine` by adding it to the `GremlinScriptEngineManager` that creates it.

    GremlinScriptEngineManager manager = new CachedGremlinScriptEngineManager();
    manager.addPlugin(ImportGremlinPlugin.build().classImports(java.awt.Color.class).create());
    GremlinScriptEngine engine = manager.getEngineByName("gremlin-groovy");

All of this new infrastructure is currently optional on the 3.2.x line of code. More detailed documentation will for these changes will be supplied as part of 3.3.0 when these features become mandatory and the deprecated code is removed.

See: TINKERPOP-1562

#### SSL Client Authentication

Added new server configuration option `ssl.needClientAuth`.

See: TINKERPOP-1602

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### CloseableIterator

Prior to TinkerPop 3.x, Blueprints had the notion of a `CloseableIterable` which exposed a way for Graph Providers to offer a way to release resources that might have been opened when returning vertices and edges. That interface was never exposed in TinkerPop 3.x, but has now been made available via the new `CloseableIterator`. Providers may choose to use this interface or not when returning values from `Graph.vertices()` and `Graph.edges()`.

It will be up to users to know whether or not they need to call `close()`. Of course, users should typically not be operating with the Graph Structure API, so it’s unlikely that they would be calling these methods directly in the first place. It is more likely that users will be calling `Traversal.close()`. This method will essentially iterate the steps of the `Traversal` and simply call `close()` on any steps that implement `AutoCloseable`. By default, `GraphStep` now implements `AutoCloseable` which most Graph Providers will extend upon (as was done with TinkerGraph’s `TinkerGraphStep`), so the integration should largely come for free if the provider simply returns a `CloseableIterator` from `Graph.vertices()` and `Graph.edges()`.

See: TINKERPOP-1589

##### HasContainer AndP Splitting

Previously, `GraphTraversal` made it easy for providers to analyze `P`-predicates in `HasContainers`, but always splitting `AndP` predicates into their component parts. This helper behavior is no longer provided because, 1.) `AndP` can be inserted into a `XXXStep` in other ways, 2.) the providers `XXXStep` should process `AndP` regardless of `GraphTraversal` helper, and 3.) the `GraphTraversal` helper did not recursively split. A simple way to split `AndP` in any custom `XXXStep` that implements `HasContainerHolder` is to use the following method:

    @Override
    public void addHasContainer(final HasContainer hasContainer) {
      if (hasContainer.getPredicate() instanceof AndP) {
        for (final P<?> predicate : ((AndP<?>) hasContainer.getPredicate()).getPredicates()) {
          this.addHasContainer(new HasContainer(hasContainer.getKey(), predicate));
        }
      } else
        this.hasContainers.add(hasContainer);
    }

See: TINKERPOP-1482, TINKERPOP-1502

##### Duplicate Multi-Properties

Added `supportsDuplicateMultiProperties` to `VertexFeatures` so that graph provider who only support unique values as multi-properties have more flexibility in describing their graph capabilities.

See: TINKERPOP-919

##### Deprecated OptIn

In 3.2.1, all `junit-benchmark` performance tests were deprecated. At that time, the `OptIn` representations of these tests should have been deprecated as well, but they were not. That omission has been remedied now. Specifically, the following fields were deprecated:

- `OptIn.SUITE_GROOVY_ENVIRONMENT_PERFORMANCE`

- `OptIn.SUITE_PROCESS_PERFORMANCE`

- `OptIn.SUITE_STRUCTURE_PERFORMANCE`

As of 3.2.4, the following test suites were also deprecated:

- `OptIn.SUITE_GROOVY_PROCESS_STANDARD`

- `OptIn.SUITE_GROOVY_PROCESS_COMPUTER`

- `OptIn.SUITE_GROOVY_ENVIRONMENT`

- `OptIn.SUITE_GROOVY_ENVIRONMENT_INTEGRATE`

Future testing of `gremlin-groovy` (and language variants in general) will be handled differently and will not require a Graph Provider to validate its operations with it. Graph Providers may now choose to remove these tests from their test suites, which should reduce the testing burden.

See: TINKERPOP-1610

##### Deprecated getInstance()

TinkerPop has generally preferred static `instance()` methods over `getInstance()`, but `getInstance()` was used in some cases nonetheless. As of this release, `getInstance()` methods have been deprecated in favor of `instance()`. Of specific note, custom `IoRegistry` (as related to IO in general) and `Supplier<ClassResolver>` (as related to Gryo serialization in general) now both prefer `instance()` over `getInstance()` given this deprecation.

See: TINKERPOP-1530

#### Drivers Providers

##### Force Close

Closing a session will first attempt a proper close of any open transactions. A problem can occur, however, if there is a long run job (e.g. an OLAP-based traversal) executing, as that job will block the calls to close the transactions. By exercising the option to a do a "forced close" the session will skip trying to close the transactions and just attempt to interrupt the long run job. By not closing transactions, the session leaves it up to the underlying graph database to sort out how it will deal with those orphaned transactions. On the positive side though (for those graphs which do that well) , long run jobs have the opportunity to be cancelled without waiting for a timeout of the job itself which will allow resources to be released earlier.

The "force" argument is passed on the "close" message and is a boolean value. This is an optional argument to "close" and defaults to `false`.

See: TINKERPOP-932, Provider Documentation - Session OpProcessor

##### SASL Authentication

Gremlin Supports SASL based authentication. The server accepts either a byte array or Base64 encoded String as the in the `sasl` argument on the `RequestMessage`, however it sends back a byte array only. Some serializers or serializer configurations don’t work well with that approach (specifically the "toString" configuration on the Gryo serializer) as the byte array is returned in the `ResponseMessage` result. In the case of the "toString" serializer the byte array gets "toString’d" and the can’t be read by the client.

In 3.2.4, the byte array is still returned in the `ResponseMessage` result, but is also returned in the status attributes under a `sasl` key as a Base64 encoded string. In this way, the client has options on how it chooses to process the authentication response and the change remains backward compatible. Drivers should upgrade to using the Base64 encoded string however as the old approach will likely be removed in the future.

See: TINKERPOP-1600

## TinkerPop 3.2.3

Release Date: October 17, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Renamed Null Result Preference

In 3.2.2, the Gremlin Console introduced a setting called `empty.result.indicator`, which controlled the output that was presented when no result was returned. For consistency, this setting has been renamed to `result.indicator.null` and can be set as follows:

    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    ==>null
    gremlin> :set result.indicator.null nil
    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    ==>nil
    gremlin> :set result.indicator.null ""
    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> graph.close()
    gremlin>

See: TINKERPOP-1409

#### Java Driver Keep-Alive

The Java Driver now has a `keepAliveInterval` setting, which controls the amount of time in milliseconds it should wait on an inactive connection before it sends a message to the server to keep the connection maintained. This should help environments that use a load balancer in front of Gremlin Server by ensuring connections are actively maintained even during periods of inactivity.

See: TINKERPOP-1249

#### Where Step Supports By-Modulation

It is now possible to use `by()` with `where()` predicate-based steps. Previously, without using `match()`, if you wanted to know who was older than their friend, the following traversal would be used.

    gremlin> g.V().as('a').out('knows').as('b').
    ......1>   filter(select('a','b').by('age').where('a', lt('b')))
    ==>v[4]

Now, with `where().by()` support, the above traversal can be expressed more succinctly and more naturally as follows.

    gremlin> g.V().as('a').out('knows').as('b').
    ......1>   where('a', lt('b')).by('age')
    ==>v[4]

See: TINKERPOP-1330

#### Change In has() Method Signatures

The TinkerPop 3.2.2 release unintentionally introduced a breaking change for some `has()` method overloads. In particular the behavior for single item array arguments was changed:

    gremlin> g.V().hasLabel(["software"] as String[]).count()
    ==>0

Prior this change single item arrays were treated like there was only that single item:

    gremlin> g.V().hasLabel(["software"] as String[]).count()
    ==>2
    gremlin> g.V().hasLabel("software").count()
    ==>2

TinkerPop 3.2.3 fixes this misbehavior and all `has()` method overloads behave like before, except that they no longer support no arguments.

#### Deprecated reconnectInitialDelay

The `reconnectInitialDelay` setting on the `Cluster` builder has been deprecated. It no longer serves any purpose. The value for the "initial delay" now comes from `reconnectInterval` (there are no longer two separate settings to control).

See: TINKERPOP-1460

#### TraversalSource.close()

`TraversalSource` now implements `AutoCloseable`, which means that the `close()` method is now available. This new method is important in cases where `withRemote()` is used, as `withRemote()` can open "expensive" resources that need to be released.

In the case of TinkerPop’s `DriverRemoteConnection`, `close()` will destroy the `Client` instance that is created internally by `withRemote()` as shown below:

    gremlin> graph = EmptyGraph.instance()
    ==>emptygraph[empty]
    gremlin> g = graph.traversal().withRemote('conf/remote-graph.properties')
    ==>graphtraversalsource[emptygraph[empty], standard]
    gremlin> g.close()
    gremlin>

Note that the `withRemote()` method will call `close()` on a `RemoteConnection` passed directly to it as well, so there is no need to do that manually.

See: TINKERPOP-790

#### IO Reference Documentation

There is new reference documentation for the various IO formats. The documentation provides more details and samples that should be helpful to users and providers who intend to work directly with the TinkerPop supported serialization formats: GraphML, GraphSON and Gryo.

See: IO Reference Documentation

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Default LazyBarrierStrategy

`LazyBarrierStrategy` has been included as a default strategy. `LazyBarrierStrategy` walks a traversal and looks for "flatMaps" (`out()`, `in()`, `both()`, `values()`, `V()`, etc.) and adds "lazy barriers" to dam up the stream so to increase the probability of bulking the traversers. One of the side-effects is that:

    g.V().out().V().has(a)

is compiled to:

    g.V().out().barrier().V().barrier().has(a)

Given that `LazyBarrierStrategy` is an `OptimizationStrategy`, it comes before `ProviderOptimizationStrategies`. Thus, if the provider’s `XXXGraphStepStrategy` simply walks from the second `V()` looking for `has()`-only, it will not be able to pull in the `has()` cause the `barrier()` blocks it. Please see the updates to `TinkerGraphStepStrategy` and how it acknowledges `NoOpBarrierSteps` (i.e. `barrier()`) skipping over them and “left”-propagating labels to the previous step.

See: TINKERPOP-1488

##### Configurable Strategies

If the provider has non-configurable `TraversalStrategy` classes, those classes should expose a static `instance()`-method. This is typical and thus, backwards compatible. However, if the provider has a `TraversalStrategy` that can be configured (e.g. via a `Builder`), then it should expose a static `create(Configuration)`-method, where the keys of the configuration are the method names of the `Builder` and the values are the method arguments. For instance, for Gremlin-Python to create a `SubgraphStrategy`, it does the following:

    g = Graph().traversal().withRemote(connection).
            withStrategies(SubgraphStrategy(vertices=__.hasLabel('person'),edges=__.has('weight',gt(0.5))))

The `SubgraphStrategy.create(Configuration)`-method is defined as:

    public static SubgraphStrategy create(final Configuration configuration) {
        final Builder builder = SubgraphStrategy.build();
        if (configuration.containsKey(VERTICES))
            builder.vertices((Traversal) configuration.getProperty(VERTICES));
        if (configuration.containsKey(EDGES))
            builder.edges((Traversal) configuration.getProperty(EDGES));
        if (configuration.containsKey(VERTEX_PROPERTIES))
            builder.vertexProperties((Traversal) configuration.getProperty(VERTEX_PROPERTIES));
        return builder.create();
    }

Finally, in order to make serialization possible from JVM-based Gremlin language variants, all strategies have a `TraverserStrategy.getConfiguration()` method which returns a `Configuration` that can be used to `create()` the `TraversalStrategy`.

The `SubgraphStrategy.getConfiguration()`-method is defined as:

    @Override
    public Configuration getConfiguration() {
        final Map<String, Object> map = new HashMap<>();
        map.put(STRATEGY, SubgraphStrategy.class.getCanonicalName());
        if (null != this.vertexCriterion)
            map.put(VERTICES, this.vertexCriterion);
        if (null != this.edgeCriterion)
                map.put(EDGES, this.edgeCriterion);
        if (null != this.vertexPropertyCriterion)
            map.put(VERTEX_PROPERTIES, this.vertexPropertyCriterion);
        return new MapConfiguration(map);
    }

The default implementation of `TraversalStrategy.getConfiguration()` is defined as:

    public default Configuration getConfiguration() {
        return new BaseConfiguration();
    }

Thus, if the provider does not have any "builder"-based strategies, then no updates to their strategies are required.

See: TINKERPOP-1455

##### Deprecated elementNotFound

Both `Graph.Exceptions.elementNotFound()` methods have been deprecated. These exceptions were being asserted in the test suite but were not being used anywhere in `gremlin-core` itself. The assertions have been modified to simply assert that `NoSuchElementException` was thrown, which is precisely the behavior that was being indirectly asserted when `Graph.Exceptions.elementNotFound()` were being used.

Providers should not need to take any action in this case for their tests to pass, however, it would be wise to remove uses of these exception builders as they will be removed in the future.

See: TINKERPOP-944

##### Hidden Step Labels for Compilation Only

In order for `SubgraphStrategy` to work, it was necessary to have multi-level children communicate with one another via hidden step labels. It was decided that hidden step labels are for compilation purposes only and will be removed prior to traversal evaluation. This is a valid decision given that hidden labels for graph system providers are not allowed to be used by users. Likewise, hidden labels for steps should not be allowed be used by users as well.

##### PropertyMapStep with Selection Traversal

`PropertyMapStep` now supports selection of properties via child property traversal. If a provider was relying solely on the provided property keys in a `ProviderOptimizationStrategy`, they will need to check if there is a child traversal and if so, use that in their introspection for respective strategies. This model was created to support `SubgraphStrategy.vertexProperties()` filtering.

See: TINKERPOP-1456, TINKERPOP-844

##### ConnectiveP Nesting Inlined

There was a bug in `ConnectiveP` (`AndP`/`OrP`), where `eq(1).and(eq(2).and(eq(3)))` was `AndP(eq(1),AndP(eq(2),eq(3)))` instead of unnested/inlined as `AndP(eq(1),eq(2),eq(3))`. Likewise, for `OrP`. If a provider was leveraging `ConnectiveP` predicates for their custom steps (e.g. graph- or vertex-centric index lookups), then they should be aware of the inlining and can simplify any and/or-tree walking code in their respective `ProviderOptimizationStrategy`.

See: TINKERPOP-1470

## TinkerPop 3.2.2

Release Date: September 6, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GraphSON 2.0

GraphSON 2.0 has been introduced to improve and normalize the format of types embedded in GraphSON.

See: TINKERPOP-1274, Reference Documentation - GraphSON 2.0.

#### Log4j Dependencies

There were a number of changes to the Log4j dependencies in the various modules. Log4j was formerly included as part of the `slf4j-log4j12` in `gremlin-core`, however that "forced" use of Log4j as a logger implementation when that really wasn’t necessary or desired. If a project depended on `gremlin-core` or other TinkerPop project to get its Log4j implementation then those applications will need to now include the dependency themselves directly.

Note that Gremlin Server and Gremlin Console explicitly package Log4j in their respective binary distributions.

See: TINKERPOP-1151

#### Default for gremlinPool

The `gremlinPool` setting in Gremlin Server is now defaulted to zero. When set to zero, Gremlin Server will use the value provided by `Runtime.availableProcessors()` to set the pool size. Note that the packaged YAML files no longer contain the thread pool settings as all are now driven by sensible defaults. Obviously these values can be added and overridden as needed.

See: TINKERPOP-1373

#### New Console Features

The Gremlin Console can now have its text colorized. For example, you can set the color of the Gremlin ascii art to the more natural color of green by using the `:set` command:

    gremlin> :set gremlin.color green

It is also possible to colorize results, like vertices, edges, and other common returns. Please see the reference documentation for more details on all the settings.

The console also now includes better multi-line support:

    gremlin> g.V().out().
    ......1>       has('name','josh').
    ......2>       out('created')
    ==>v[5]
    ==>v[3]

This is a nice feature in that it can help you understand if a line is incomplete and unevaluated.

See: TINKERPOP-1285, TINKERPOP-1037, Reference Documentation - Console Preferences

#### REST API Renamed to HTTP API

This is only a rename to clarify the design of the API. There is no change to the API itself.

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Deprecated Io.Builder.registry()

The `Io.Builder.registry()` has been deprecated in favor of `Io.Builder.onMapper(Consumer<Mapper>)`. This change gives the `Graph` implementation greater flexibility over how to modify the `Mapper` implementation. In most cases, the implementation will simply add its `IoRegistry` to allow the `Mapper` access to custom serialization classes, but this approach makes it possible to also set other specific settings that aren’t generalized across all IO implementations. A good example of this type of usage would be to provide a custom `ClassRessolver` implementation to a `GryoMapper`.

See: TINKERPOP-1402

##### Log4j Dependencies

There were a number of changes to the Log4j dependencies in the various modules. Log4j was formerly included as part of the `slf4j-log4j12` in `gremlin-core`, however that "forced" use of log4j as a logger implementation when that really wasn’t necessary or desired. The `slf4j-log4j12` dependency is now in "test" scope for most of the modules. The exception to that rule is `gremlin-test` which prescribes it as "optional". That change means that developers dependending on `gremlin-test` (or `gremlin-groovy-test`) will need to explicitly specify it as a dependency in their `pom.xml` (or a different slf4j implementation if that better suits them).

See: TINKERPOP-1151

#### Drivers Providers

##### GraphSON 2.0

Drivers providers can exploit the new format of typed values JSON serialization offered by GraphSON 2.0. This format has been created to allow easy and agnostic parsing of a GraphSON payload without type loss. Drivers of non-Java languages can then implement their own mapping of the GraphSON’s language agnostic type IDs (e.g. `UUID`, `LocalDate`) to the appropriate representation for the driver’s language.

See: TINKERPOP-1274, Reference Documentation - GraphSON 2.0.

##### Traversal Serialization

There was an "internal" serialization format in place for `Traversal` which allowed one to be submitted to Gremlin Server directly over `RemoteGraph`. That format has been removed completely and is wholly replaced by the non-JVM specific approach of serializing `Bytecode`.

See: TINKERPOP-1392

## TinkerPop 3.2.1

Release Date: July 18, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gephi Plugin

The Gephi Plugin has been updated to support Gephi 0.9.x. Please upgrade to this latest version to use the Gephi Plugin for Gremlin Console.

See: TINKERPOP-1297

#### GryoMapper Construction

It is now possible to override existing serializers with calls to `addCustom` on the `GryoMapper` builder. This option allows complete control over the serializers used by Gryo. Of course, this also makes it possible to produce completely non-compliant Gryo files. This feature should be used with caution.

#### TraversalVertexProgram

`TraversalVertexProgram` always maintained a `HALTED_TRAVERSERS` `TraverserSet` for each vertex throughout the life of the OLAP computation. However, if there are no halted traversers in the set, then there is no point in keeping that compute property around as without it, time and space can be saved. Users that have `VertexPrograms` that are chained off of `TraversalVertexProgram` and have previously assumed that `HALTED_TRAVERSERS` always exists at each vertex, should no longer assume that.

    TraverserSet haltedTraversers = vertex.value(TraversalVertexProgram.HALTED_TRAVERSERS);
    // good code
    TraverserSet haltedTraversers = vertex.property(TraversalVertexProgram.HALTED_TRAVERSERS).orElse(new TraverserSet());

#### Interrupting Traversals

Traversals now better respect calls to `Thread.interrupt()`, which mean that a running `Traversal` can now be cancelled. There are some limitations that remain, but most OLTP-based traversals should cancel without issue. OLAP-based traversals for Spark will also cancel and clean up running jobs in Spark itself. Mileage may vary on other process implementations and it is possible that graph providers could potentially write custom step implementations that prevent interruption. If it is found that there are configurations or specific traversals that do not respect interruption, please mention them on the mailing list.

See: TINKERPOP-946

#### Gremlin Console Flags

Gremlin Console had several methods for executing scripts from file at the start-up of `bin/gremlin.sh`. There were two options:

    bin/gremlin.sh script.groovy    //1
    bin/gremlin.sh -e script.groovy //2

1. The `script.groovy` would be executed as a console initialization script setting the console up for use and leaving it open when the script completed successfully or closing it if the script failed.

2. The `script.groovy` would be executed by the `ScriptExecutor` which meant that commands for the Gremlin Console, such as `:remote` and `:>` would not be respected.

Changes in this version of TinkerPop have added much more flexibility here and only a minor breaking change should be considered when using this version. First of all, recognize that hese two lines are currently equivalent:

    bin/gremlin.sh script.groovy
    bin/gremlin.sh -i script.groovy

but users should start to explicitly specify the `-i` flag as TinkerPop will eventually remove the old syntax. Despite the one used beware of the fact that neither will close the console on script failure anymore. In that sense, this behavior represents a breaking change to consider. To ensure the console closes on failure or success, a script will have to use the `-e` option.

The console also has a number of new features in addition to `-e` and `-i`:

- View the available flags for the console with `-h`.

- Control console output with `-D`, `-Q` and -`V`

- Get line numbers on script failures passed to `-i` and `-e`.

See: TINKERPOP-1268, TINKERPOP-1155, TINKERPOP-1156, TINKERPOP-1157, Reference Documentation - Interactive Mode, Reference Documentation - Execution Mode

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### VertexComputing API Change

The `VertexComputing` API is used by steps that wrap a `VertexProgram`. There is a method called `VertexComputing.generateProgram()` that has changed which now takes a second argument of `Memory`. To upgrade, simply fix the method signature of your `VertexComputing` implementations. The `Memory` argument can be safely ignored to effect the exact same semantics as prior. However, now previous OLAP job `Memory` can be leveraged when constructing the next `VertexProgram` in an OLAP traversal chain.

##### Interrupting Traversals

Several tests have been added to the TinkerPop test suite to validate that a `Traversal` can be cancelled with `Thread.interrupt()`. The test suite does not cover all possible traversal scenarios. When implementing custom steps, providers should take care to not ignore an `InterruptionException` that might be thrown in their code and to be sure to check `Thread.isInterrupted()` as needed to ensure that the step remains cancellation compliant.

See: TINKERPOP-946

##### Performance Tests

All "performance" tests have been deprecated. In the previous 3.2.0-incubating release, the `ProcessPerformanceSuite` and `TraversalPerformanceTest` were deprecated, but some other tests remained. It is the remaining tests that have been deprecated on this release:

- `StructurePerformanceSuite

  - `GraphReadPerformanceTest`

  - `GraphWriterPerformanceTest`

- `GroovyEnvironmentPerformanceSuite`

  - `SugarLoaderPerformanceTest`

  - `GremlinExecutorPerformanceTest`

- Gremlin Server related performance tests

- TinkerGraph related performance tests

Providers should implement their own performance tests and not rely on these deprecated tests as they will be removed in a future release along with the "JUnit Benchmarks" dependency.

See: TINKERPOP-1294

#### Graph Database Providers

##### Transaction Tests

Tests and assertions were added to the structure test suite to validate that transaction status was in the appropriate state following calls to close the transaction with `commit()` or `rollback()`. It is unlikely that this change would cause test breaks for providers, unless the transaction status was inherently disconnected from calls to close the transaction somehow.

In addition, other tests were added to enforce the expected semantics for threaded transactions. Threaded transactions are expected to behave like manual transactions. They should be open automatically when they are created and once closed should no longer be used. This behavior is not new and is the typical expected method for working with these types of transactions. The test suite just requires that the provider implementation conform to these semantics.

See: TINKERPOP-947, TINKERPOP-1059

##### GraphFilter and GraphFilterStrategy

`GraphFilter` has been significantly advanced where the determination of an edge direction/label legality is more stringent. Along with this, `GraphFilter.getLegallyPositiveEdgeLabels()` has been added as a helper method to make it easier for `GraphComputer` providers to know the space of labels being accessed by the traversal and thus, better enable provider-specific push-down predicates.

Note that `GraphFilterStrategy` is now a default `TraversalStrategy` registered with `GraphComputer.` If `GraphFilter` is expensive for the underlying `GraphComputer` implementation, it can be deactivated as is done for `TinkerGraphComputer`.

    static {
      TraversalStrategies.GlobalCache.registerStrategies(TinkerGraphComputer.class,
        TraversalStrategies.GlobalCache.getStrategies(GraphComputer.class).clone().removeStrategies(GraphFilterStrategy.class));
    }

See: TINKERPOP-1293

#### Graph Language Providers

##### VertexTest Signatures

The method signatures of `get_g_VXlistXv1_v2_v3XX_name` and `get_g_VXlistX1_2_3XX_name` of `VertexTest` were changed to take arguments for the `Traversal` to be constructed by extending classes.

## TinkerPop 3.2.0

Release Date: Release Date: April 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Hadoop FileSystem Variable

The `HadoopGremlinPlugin` defines two variables: `hdfs` and `fs`. The first is a reference to the HDFS `FileSystemStorage` and the latter is a reference to the local `FileSystemStorage`. Prior to 3.2.x, `fs` was called `local`. However, there was a variable name conflict with `Scope.local`. As such `local` is now `fs`. This issue existed prior to 3.2.x, but was not realized until this release. Finally, this only effects Gremlin Console users.

#### Hadoop Configurations

Note that `gremlin.hadoop.graphInputFormat`, `gremlin.hadoop.graphOutputFormat`, `gremlin.spark.graphInputRDD`, and `gremlin.spark.graphOuputRDD` have all been deprecated. Using them still works, but moving forward, users only need to leverage `gremlin.hadoop.graphReader` and `gremlin.hadoop.graphWriter`. An example properties file snippet is provided below.

    gremlin.graph=org.apache.tinkerpop.gremlin.hadoop.structure.HadoopGraph
    gremlin.hadoop.graphReader=org.apache.tinkerpop.gremlin.hadoop.structure.io.gryo.GryoInputFormat
    gremlin.hadoop.graphWriter=org.apache.tinkerpop.gremlin.hadoop.structure.io.gryo.GryoOutputFormat
    gremlin.hadoop.jarsInDistributedCache=true
    gremlin.hadoop.defaultGraphComputer=org.apache.tinkerpop.gremlin.spark.process.computer.SparkGraphComputer

See: TINKERPOP-1082, TINKERPOP-1222

#### TraversalSideEffects Update

There were changes to `TraversalSideEffect` both at the semantic level and at the API level. Users that have traversals of the form `sideEffect{…​}` that leverage global side-effects should read the following carefully. If the user’s traversals do not use lambda-based side-effect steps (e.g. `groupCount("m")`), then the changes below will not effect them. Moreover, if user’s traversal only uses `sideEffect{…​}` with closure (non-`TraversalSideEffect`) data references, then the changes below will not effect them. If the user’s traversal uses sideEffects in OLTP only, the changes below will not effect them. Finally, providers should not be effected by the changes save any tests cases.

##### TraversalSideEffects Get API Change

`TraversalSideEffects` can now logically operate within a distributed OLAP environment. In order to make this possible, it is necessary that each side-effect be registered with a reducing `BinaryOperator`. This binary operator will combine distributed updates into a single global side-effect at the master traversal. Many of the methods in `TraversalSideEffect` have been `Deprecated`, but they are backwards compatible save that `TraversalSideEffects.get()` no longer returns an `Optional`, but instead throws an `IllegalArgumentException`. While the `Optional` semantics could have remained, it was deemed best to directly return the side-effect value to reduce object creation costs and because all side-effects must be registered apriori, there is never a reason why an unknown side-effect key would be used. In short:

    // change
    traversal.getSideEffects().get("m").get()
    // to
    traversal.getSideEffects().get("m")

##### TraversalSideEffects Registration Requirement

All `TraversalSideEffects` must be registered upfront. This is because, in OLAP, side-effects map to `Memory` compute keys and as such, must be declared prior to the execution of the `TraversalVertexProgram`. If a user’s traversal creates a side-effect mid-traversal, it will fail. The traversal must use `GraphTraversalSource.withSideEffect()` to declare the side-effects it will use during its execution lifetime. If the user’s traversals use standard side-effect Gremlin steps (e.g. `group("m")`), then no changes are required.

See: TINKERPOP-1192

##### TraversalSideEffects Add Requirement

In a distributed environment, a side-effect can not be mutated and be expected to exist in the mutated form at the final, aggregated, master traversal. For instance, if the side-effect "myCount" references a `Long`, the `Long` can not be updated directly via `sideEffects.set("myCount", sideEffects.get("myCount") + 1)`. Instead, it must rely on the registered reducer to do the merging and thus, the `Step` must do `sideEffect.add("mySet",1)`, where the registered reducer is `Operator.sum`. Thus, the below will increment "a". If no operator was provided, then the operator is assumed `Operator.assign` and the final result of "a" would be 1. Note that `Traverser.sideEffects(key,value)` uses `TraversalSideEffect.add()`.

    gremlin> traversal = g.withSideEffect('a',0,sum).V().out().sideEffect{it.sideEffects('a',1)}
    ==>v[3]
    ==>v[2]
    ==>v[4]
    ==>v[5]
    ==>v[3]
    ==>v[3]
    gremlin> traversal.getSideEffects().get('a')
    ==>6
    gremlin> traversal = g.withSideEffect('a',0).V().out().sideEffect{it.sideEffects('a',1)}
    ==>v[3]
    ==>v[2]
    ==>v[4]
    ==>v[5]
    ==>v[3]
    ==>v[3]
    gremlin> traversal.getSideEffects().get('a')
    ==>1

See: TINKERPOP-1192, TINKERPOP-1166

#### ProfileStep Update and GraphTraversal API Change

The `profile()`-step has been refactored into 2 steps —`ProfileStep` and `ProfileSideEffectStep`. Users who previously used the `profile()` in conjunction with `cap(TraversalMetrics.METRICS_KEY)` can now simply omit the cap step. Users who retrieved `TraversalMetrics` from the side-effects after iteration can still do so, but will need to specify a side-effect key when using the `profile()`. For example, `profile("myMetrics")`.

See: TINKERPOP-958

#### BranchStep Bug Fix

There was a bug in `BranchStep` that also rears itself in subclass steps such as `UnionStep` and `ChooseStep`. For traversals with branches that have barriers (e.g. `count()`, `max()`, `groupCount()`, etc.), the traversal needs to be updated. For instance, if a traversal is of the form `g.V().union(out().count(),both().count())`, the result is now different (the bug fix yields a different output). In order to yield the same result, the traversal should be rewritten as `g.V().local(union(out().count(),both().count()))`. Note that if a branch does not have a barrier, then no changes are required. For instance, `g.V().union(out(),both())` does not need to be updated. Moreover, if the user’s traversal already used the `local()`-form, then no change are required either.

See: TINKERPOP-1188

#### MemoryComputeKey and VertexComputeKey

Users that have custom `VertexProgram` implementations will need to change their implementations to support the new `VertexComputeKey` and `MemoryComputeKey` classes. In the `VertexPrograms` provided by TinkerPop, these changes were trivial, taking less than 5 minutes to make all the requisite updates.

- `VertexProgram.getVertexComputeKeys()` returns a `Set<VertexComputeKey>`. No longer a `Set<String>`. Use `VertexComputeKey.of(String key,boolean transient)` to generate a `VertexComputeKey`. Transient keys were not supported in the past, so to make the implementation semantically equivalent, the boolean transient should be false.

- `VertexProgram.getMemoryComputeKeys()` returns a `Set<MemoryComputeKey>`. No longer a `Set<String>`. Use `MemoryComputeKey.of(String key, BinaryOperator reducer, boolean broadcast, boolean transient)` to generate a `MemoryComputeKey`. Broadcasting and transients were not supported in the past so to make the implementation semantically equivalent, the boolean broadcast should be true and the boolean transient should be false.

An example migration looks as follows. What might currently look like:

    public Set<String> getMemoryComputeKeys() {
       return new HashSet<>(Arrays.asList("a","b","c"))
    }

Should now look like:

    public Set<MemoryComputeKey> getMemoryComputeKeys() {
      return new HashSet<>(Arrays.asList(
        MemoryComputeKey.of("a", Operator.and, true, false),
        MemoryComputeKey.of("b", Operator.sum, true, false),
        MemoryComputeKey.of("c", Operator.or, true, false)))
    }

A similar patterns should also be used for `VertexProgram.getVertexComputeKeys()`.

See: TINKERPOP-1162

#### SparkGraphComputer and GiraphGraphComputer Persistence

The `MapReduce`-based steps in `TraversalVertexProgram` have been removed and replaced using a new `Memory`-reduction model. `MapReduce` jobs always created a persistence footprint, e.g. in HDFS. `Memory` data was never persisted to HDFS. As such, there will be no data on the disk that is accessible. For instance, there is no more `~reducing`, `~traversers`, and specially named side-effects such as `m` from a `groupCount('m')`. The data is still accessible via `ComputerResult.memory()`, it simply does not have a corresponding on-disk representation.

#### RemoteGraph

`RemoteGraph` is a lightweight `Graph` implementation that acts as a proxy for sending traversals to Gremlin Server for remote execution. It is an interesting alternative to the other methods for connecting to Gremlin Server in that all other methods involved construction of a `String` representation of the `Traversal` which is then submitted as a script to Gremlin Server (via driver or HTTP).

    gremlin> graph = RemoteGraph.open('conf/remote-graph.properties')
    ==>remotegraph[DriverServerConnection-localhost/127.0.0.1:8182 [graph='graph]]
    gremlin> g = graph.traversal()
    ==>graphtraversalsource[remotegraph[DriverServerConnection-localhost/127.0.0.1:8182 [graph='graph]], standard]
    gremlin> g.V().valueMap(true)
    ==>[name:[marko], label:person, id:1, age:[29]]
    ==>[name:[vadas], label:person, id:2, age:[27]]
    ==>[name:[lop], label:software, id:3, lang:[java]]
    ==>[name:[josh], label:person, id:4, age:[32]]
    ==>[name:[ripple], label:software, id:5, lang:[java]]
    ==>[name:[peter], label:person, id:6, age:[35]]

Note that `g.V().valueMap(true)` is executing in Gremlin Server and not locally in the console.

See: TINKERPOP-575, Reference Documentation - Remote Graph

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### GraphStep Compilation Requirement

OLTP graph providers that have a custom `GraphStep` implementation should ensure that `g.V().hasId(x)` and `g.V(x)` compile to the same representation. This ensures a consistent user experience around random access of elements based on ids (as opposed to potentially the former doing a linear scan). A static helper method called `GraphStep.processHasContainerIds()` has been added. `TinkerGraphStepStrategy` was updated as such:

    ((HasContainerHolder) currentStep).getHasContainers().forEach(tinkerGraphStep::addHasContainer);

is now

    ((HasContainerHolder) currentStep).getHasContainers().forEach(hasContainer -> {
      if (!GraphStep.processHasContainerIds(tinkerGraphStep, hasContainer))
        tinkerGraphStep.addHasContainer(hasContainer);
    });

See: TINKERPOP-1219

##### Step API Update

The `Step` interface is fundamental to Gremlin. `Step.processNextStart()` and `Step.next()` both returned `Traverser<E>`. We had so many `Traverser.asAdmin()` and direct typecast calls throughout (especially in `TraversalVertexProgram`) that it was deemed prudent to have `Step.processNextStart()` and `Step.next()` return `Traverser.Admin<E>`. Moreover it makes sense as this is internal logic where `Admins` are always needed. Providers with their own step definitions will simply need to change the method signatures of `Step.processNextStart()` and `Step.next()`. No logic update is required — save that `asAdmin()` can be safely removed if used. Also, `Step.addStart()` and `Step.addStarts()` take `Traverser.Admin<S>` and `Iterator<Traverser.Admin<S>>`, respectively.

##### Traversal API Update

The way in which `TraverserRequirements` are calculated has been changed (for the better). The ramification is that post compilation requirement additions no longer make sense and should not be allowed. To enforce this, `Traversal.addTraverserRequirement()` method has been removed from the interface. Moreover, providers/users should never be able to add requirements manually (this should all be inferred from the end compilation). However, if need be, there is always `RequirementStrategy` which will allow the provider to add a requirement at strategy application time (though again, there should not be a reason to do so).

##### ComparatorHolder API Change

Providers that either have their own `ComparatorHolder` implementation or reason on `OrderXXXStep` will need to update their code. `ComparatorHolder` now returns `List<Pair<Traversal,Comparator>>`. This has greatly reduced the complexity of comparison-based steps like `OrderXXXStep`. However, its a breaking API change that is trivial to update to, just some awareness is required.

See: TINKERPOP-1209

##### GraphComputer Semantics and API

Providers that have a custom `GraphComputer` implementation will have a lot to handle. Note that if the graph system simply uses `SparkGraphComputer` or `GiraphGraphComputer` provided by TinkerPop, then no updates are required. This only effects providers that have their own custom `GraphComputer` implementations.

`Memory` updates:

- Any `BinaryOperator` can be used for reduction and is made explicit in the `MemoryComputeKey`.

- `MemoryComputeKeys` can be marked transient and must be removed from the resultant `ComputerResult.memory()`.

- `MemoryComputeKeys` can be specified to not broadcast and thus, must not be available to workers to read in `VertexProgram.execute()`.

- The `Memory` API has been changed. No more `incr()`, `and()`, etc. Now its just `set()` (setup/terminate) and `add()` (execute).

`VertexProgram` updates:

- `VertexComputeKeys` can be marked transient and must be removed from the resultant `ComputerResult.graph()`.

See: TINKERPOP-1166, TINKERPOP-1164, TINKERPOP-951

Operational semantic test cases have been added to `GraphComputerTest` to ensure that all the above are implemented correctly.

##### Barrier Step Updates

The `Barrier` interface use to simply be a marker interface. Now it has methods and it is the primary means by which distributed steps across an OLAP job are aggregated and distributed. It is unlikely that `Barrier` was ever used directly by a provider’s custom step. Instead, a provider most likely extended `SupplyingBarrierStep`, `CollectingBarrierStep`, and/or `ReducingBarrierStep`.

Providers that have custom extensions to these steps or that use `Barrier` directly will need to adjust their implementation slightly to accommodate a new API that reflects the `Memory` updates above. This should be a simple change. Note that `FinalGet` no longer exists and such post-reduction processing is handled by the reducing step (via the new `Generating` interface).

See: TINKERPOP-1164

##### Performance Tests

The `ProcessPerformanceSuite` and `TraversalPerformanceTest` have been deprecated. They are still available, but going forward, providers should implement their own performance tests and not rely on the built-in JUnit benchmark-based performance test suite.

#### Graph Processor Providers

##### GraphFilter and GraphComputer

The `GraphComputer` API has changed with the addition of `GraphComputer.vertices(Traversal)` and `GraphComputer.edges(Traversal)`. These methods construct a `GraphFilter` object which is also new to TinkerPop 3.2.0. `GraphFilter` is a "push-down predicate" used to selectively retrieve subgraphs of the underlying graph to be OLAP processed.

- If the graph system provider relies on an existing `GraphComputer` implementations such as `SparkGraphComputer` and/or `GiraphGraphComputer`, then there is no immediate action required on their part to remain TinkerPop-compliant. However, they may wish to update their `InputFormat` or `InputRDD` implementation to be `GraphFilterAware` and handle the `GraphFilter` filtering at the disk/database level. It is advisable to do so in order to reduce OLAP load times and memory/GC usage.

- If the graph system provider has their own `GraphComputer` implementation, then they should implement the two new methods and ensure that `GraphFilter` is processed correctly. There is a new test case called `GraphComputerTest.shouldSupportGraphFilter()` which ensures the semantics of `GraphFilter` are handled correctly. For a "quick and easy" way to move forward, look to `GraphFilterInputFormat` as a way of wrapping an existing `InputFormat` to do filtering prior to `VertexProgram` or `MapReduce` execution.

Note | To quickly move forward, the `GraphComputer` implementation can simply set `GraphComputer.Features.supportsGraphFilter()` to `false` and ensure that `GraphComputer.vertices()` and `GraphComputer.edges()` throws `GraphComputer.Exceptions.graphFilterNotSupported()`. This is not recommended as its best to support `GraphFilter`.

See: TINKERPOP-962

##### Job Chaining and GraphComputer

TinkerPop 3.2.0 has integrated `VertexPrograms` into `GraphTraversal`. This means, that a single traversal can compile to multiple `GraphComputer` OLAP jobs. This requires that `ComputeResults` be chainable. There was never any explicit tests to verify if a provider’s `GraphComputer` could be chained, but now there are. Given a reasonable implementation, it is likely that no changes are required of the provider. However, to ensure the implementation is "reasonable" `GraphComputerTests` have been added.

- For providers that support their own `GraphComputer` implementation, note that there is a new `GraphComputerTest.shouldSupportJobChaining()`. This tests verifies that the `ComputerResult` output of one job can be fed into the input of a subsequent job. Only linear chains are tested/required currently. In the future, branching DAGs may be required.

- For providers that support their own `GraphComputer` implementation, note that there is a new `GraphComputerTest.shouldSupportPreExistingComputeKeys()`. When chaining OLAP jobs together, if an OLAP job requires the compute keys of a previous OLAP job, then the existing compute keys must be accessible. A simple 2 line change to `SparkGraphComputer` and `TinkerGraphComputer` solved this for TinkerPop. `GiraphGraphComputer` did not need an update as this feature was already naturally supported.

See: TINKERPOP-570

#### Graph Language Providers

##### ScriptTraversal

Providers that have custom Gremlin language implementations (e.g. Gremlin-Scala), there is a new class called `ScriptTraversal` which will handle script-based processing of traversals. The entire `GroovyXXXTest`-suite was updated to use this new class. The previous `TraversalScriptHelper` class has been deprecated so immediate upgrading is not required, but do look into `ScriptTraversal` as TinkerPop will be using it as a way to serialize "String-based traversals" over the network moving forward.

See: TINKERPOP-1154

##### ByModulating and Custom Steps

If the provider has custom steps that leverage `by()`-modulation, those will now need to implement `ByModulating`. Most of the methods in `ByModulating` are `default` and, for most situations, only `ByModulating.modulateBy(Traversal)` needs to be implemented. Note that this method’s body will most like be identical the custom step’s already existing `TraversalParent.addLocalChild()`. It is recommended that the custom step not use `TraversalParent.addLocalChild()` as this method may be deprecated in a future release. Instead, barring any complex usages, simply rename the `CustomStep.addLocalChild(Traversal)` to `CustomStep.modulateBy(Traversal)`.

See: TINKERPOP-1153

##### TraversalEngine Deprecation and GraphProvider

The `TraversalSource` infrastructure has been completely rewritten. Fortunately for users, their code is backwards compatible. Unfortunately for graph system providers, a few tweaks to their implementation are in order.

- If the graph system supports more than `Graph.compute()`, then implement `GraphProvider.getGraphComputer()`.

- For custom `TraversalStrategy` implementations, change `traverser.getEngine().isGraphComputer()` to `TraversalHelper.onGraphComputer(Traversal)`.

- For custom `Steps`, change `implements EngineDependent` to `implements GraphComputing`.

See: TINKERPOP-971

# TinkerPop 3.1.0

A 187 On The Undercover Gremlinz

## TinkerPop 3.1.8

Release Date: August 21, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

## TinkerPop 3.1.7

Release Date: June 12, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### GraphML XSLT

There were some inconsistencies in the GraphML format supported in TinkerPop 2.x. These issues were corrected on the initial release of TinkerPop 3.0.0, but as a result, attempting to read GraphML from 2.x will end with an error. A newly added XSLT file in `gremlin-core`, called `tp2-to-tp3-graphml.xslt`, transforms 2.x GraphML into 3.x GraphML, making it possible easily read in legacy GraphML through a 3.x `GraphMLReader`.

See: TINKERPOP-1608

## TinkerPop 3.1.6

Release Date: February 3, 2017

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Providers

#### Driver Providers

##### Session Close Confirmation

When a session is closed, it now returns a confirmation in the form of a single `NO CONTENT` message. When the message arrives, it means that the server has already destroyed the session. Prior to this change, the request was somewhat one-way, in that the client could send the request and the server would silently honor it. The confirmation makes it a bit easier to ensure from the client perspective that the close did what it was supposed to do, allowing the client to proceed only when the server was fully complete with its work.

See: TINKERPOP-1544

## TinkerPop 3.1.5

Release Date: October 17, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Java Driver and close()

There were a few problems noted around the `close()` of `Cluster` and `Client` instances, including issues that presented as system hangs. These issues have been resolved, however, it is worth noting that an unchecked exception that was thrown under a certain situation has changed as part of the bug fixes. When submitting an in-session request on a `Client` that was closed (or closing) an `IllegalStateException` is thrown. This replaces older functionality that threw a `ConnectionException` and relied logic far deeper in the driver to produce that error and had the potential to open additional resources despite the intention of the user to "close".

See: TINKERPOP-1467

## TinkerPop 3.1.4

Release Date: September 6, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Server Workers

In release 3.1.3, a recommendation was made to ensure that the `threadPoolWorker` setting for Gremlin Server was no less than `2` in cases where Gremlin Server was being used with sessions that accept parallel requests. In 3.1.4, that is no longer the case and a size of `1` remains acceptable even in that specific case.

See: TINKERPOP-1350

## TinkerPop 3.1.3

Release Date: July 18, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Reserved Gremlin Server Keys

Gremlin Server has always considered certain binding keys (request parameters) as reserved, but that list has now expanded to be more inclusive all the static enums that are imported to the script engine. It is possible that those using Gremlin Server may have to rename their keys if they somehow successfully were using some of the now reserved terms in previous versions.

See: TINKERPOP-1354

#### Remote Timeout

Disabling the timeout for a `:remote` to Gremlin Server was previously accomplished by setting the timeout to `max` as in:

    :remote config timeout max

where `max` would set the timeout to be `Integer.MAX_VALUE`. While this feature is still supported, it has been deprecated in favor of the new configuration option of `none`, as in:

    :remote config timeout none

The use of `none` completely disables the timeout rather than just setting an arbitrarily high one. Note that it is still possible to get a timeout on a request if the server timeout limits are reached. The console timeout value only refers to how long the console will wait for a response from the server before giving up. By default, the timeout is set to `none`.

See: TINKERPOP-1267

#### Gremlin Server Workers

Past configuration recommendations for the `threadPoolWorker` setting on Gremlin Server stated this value could be safely set to `1` at the low end. A size of `1` is still valid for most cases, however, if Gremlin Server is being used with sessions that accept parallel requests, then this value should be no less than `2` or else certain scripts (i.e. those that block for an extended period of time) may cause Gremlin Server to lock up the session.

See: TINKERPOP-1350

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph Database Providers

##### Property Keys and Hyphens

Graph providers should no longer rely on the test suite to validate that hyphens work for labels and property keys.

##### Vertex and Edge Counts

A large number of asserts for vertex and edge counts in the test suite were not being applied. This problem has been rectified, but could manifest as test errors for different implementations. The chances of the new assertions identifying previously unrecognized bugs seems slim however, as there are many other tests that validate these counts in other ways. If those were passing previously, then these new asserts should likely not pose a problem.

See: TINKERPOP-1300

##### Test Feature Annotations

A large number of `gremlin-test` feature annotations were incorrect which caused test cases to run against graphs that did not support those features. The annotations have been fixed, but this opened the possibility that more test cases will run against the graph implementation. Providers should ensure that their graph `features()` are consistent with the capabilities of the graph implementation.

See: TINKERPOP-1319

#### Graph Language Providers

##### AndTest Renaming

The `get_g_V_andXhasXage_gt_27XoutE_count_gt_2X_name` test in `AndTest` was improperly named and did not match the nature of the traversal it was providing. It has been renamed to: `get_g_V_andXhasXage_gt_27XoutE_count_gte_2X_name`.

#### Driver Providers

##### SASL Mechanism

Note that the Gremlin Driver for Java now passes a new parameter for SASL authentication called `saslMechanism`. This is an optional argument and does not represent a breaking change, but it does make the overall implementation more complete. While the default authentication implementations packaged with Gremlin Server don’t utilize this argument other implementations might, so the drivers should be able to pass it as per the SASL specification.

See: TINKERPOP-1263

## TinkerPop 3.1.2

Release Date: April 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Aliasing Sessions

Calls to `SessionedClient.alias()` used to throw `UnsupportedOperationException` and it was therefore not possible to use that capability with a session. That method is now properly implemented and aliasing is allowed.

See: TINKERPOP-1096

#### Remote Console

The `:remote console` command provides a way to avoid having to prefix the `:>` command to scripts when remoting. This mode of console usage can be convenient when working exclusively with a remote like Gremlin Server and there is only a desire to view the returned data and not to actually work with it locally in any way.

See: Reference Documentation - Remote Console

#### Console Remote Sessions

The `:remote tinkerpop.server` command now allows for a "session" argument to be passed to `connect`. This argument, tells the remote to configure it with a Gremlin Server session. In this way, the console can act as a window to script exception on the server and behave more like a standard "local" console when it comes to script execution.

See: TINKERPOP-1097

#### TinkerPop Archetypes

TinkerPop now offers Maven archetypes, which provide example project templates to quickly get started with TinkerPop. The available archetypes are as follows:

- `gremlin-archetype-server` - An example project that demonstrates the basic structure of a Gremlin Server project, how to connect with the Gremlin Driver, and how to embed Gremlin Server in a testing framework.

- `gremlin-archetype-tinkergraph` - A basic example of how to structure a TinkerPop project with Maven.

See: TINKERPOP-1085, Reference Documentation - Archetypes

#### Session Transaction Management

When connecting to a session with `gremlin-driver`, it is now possible to configure the `Client` instance so as to request that the server manage the transaction for each requests.

    Cluster cluster = Cluster.open();
    Client client = cluster.connect("sessionName", true);

Specifying `true` to the `connect()` method signifies that the `client` should make each request as one encapsulated in a transaction. With this configuration of `client` there is no need to close a transaction manually.

See: TINKERPOP-1039, Reference Documentation - Considering Sessions

#### Session Timeout Setting

The `gremlin-driver` now has a setting called `maxWaitForSessionClose` that allows control of how long it will wait for an in-session connection to respond to a close request before it simply times-out and moves on. When that happens, the server will either eventually close the connection via at session expiration or at the time of shutdown.

See: TINKERPOP-1160

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### All Providers

##### Provider Documentation

Documentation related to the lower-level APIs used by a provider, that was formerly in the reference documentation, has been moved to its own documentation set that is now referred to as the Provider Documentation.

See: TINKERPOP-937

#### Graph System Providers

##### GraphProvider.clear() Semantics

The semantics of the various `clear()` methods on `GraphProvider` didn’t really change, but it would be worth reviewing their implementations to ensure that implementations can be called successfully in an idempotent fashion. Multiple calls to `clear()` may occur for a single test on the same `Graph` instance, as `3.1.1-incubating` introduced an automated method for clearing graphs at the end of a test and some tests call `clear()` manually.

See: TINKERPOP-1146

#### Driver Providers

##### Session Transaction Management

Up until now transaction management has been a feature of sessionless requests only, but the new `manageTransaction` request argument for the Session OpProcessor changes that. Session-based requests can now pass this boolean value on each request to signal to Gremlin Server that it should attempt to commit (or rollback) the transaction at the end of the request. By default, this value as `false`, so there is no change to the protocol for this feature.

See: TINKERPOP-1039, Reference Documentation - Considering Sessions

##### scriptEvalTimeout Override

The Gremlin Server protocol now allows the passing of `scriptEvaluationTimeout` as an argument to the `SessionOpProcessor` and the `StandardOpProcessor`. This value will override the setting of the same name provided in the Gremlin Server configuration file on a per request basis.

#### Plugin Providers

##### RemoteAcceptor allowRemoteConsole

The `RemoteAcceptor` now has a new method called `allowRemoteConsole()`. It has a default implementation that returns `false` and should thus be a non-breaking change for current implementations. This value should only be set to `true` if the implementation expects the user to always use `:>` to interact with it. For example, the `tinkerpop.server` plugin expects all user interaction through `:>`, where the line is sent to Gremlin Server. In that case, that `RemoteAcceptor` implementation can return `true`. On the other hand, the `tinkerpop.gephi` plugin, expects that the user sometimes call `:>` and sometimes work with local evaluation as well. It interacts with the local variable bindings in the console itself. For `tinkerpop.gephi`, this method returns `false`.

See: Reference Documentation - Remote Console

## TinkerPop 3.1.1

Release Date: February 8, 2016

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Storage I/O

The `gremlin-core` io-package now has a `Storage` interface. The methods that were available via `hdfs` (e.g. `rm()`, `ls()`, `head()`, etc.) are now part of `Storage`. Both HDFS and Spark implement `Storage` via `FileSystemStorage` and `SparkContextStorage`, respectively. `SparkContextStorage` adds support for interacting with persisted RDDs in the Spark cache.

This update changed a few of the file handling methods. As it stands, these changes only effect manual Gremlin Console usage as HDFS support was previously provided via Groovy meta-programing. Thus, these are not "code-based" breaking changes.

- `hdfs.rmr()` no longer exists. `hdfs.rm()` is now recursive. Simply change all references to `rmr()` to `rm()` for identical behavior.

- `hdfs.head(location,lines,writableClass)` no longer exists.

  - For graph locations, use `hdfs.head(location,writableClass,lines)`.

  - For memory locations, use `hdfs.head(location,memoryKey,writableClass,lines)`.

- `hdfs.head(…​,ObjectWritable)` no longer exists. Use `SequenceFileInputFormat` as an input format is the parsing class.

Given that HDFS (and now Spark) interactions are possible via `Storage` and no longer via Groovy meta-programming, developers can use these `Storage` implementations in their Java code. In fact, `Storage` has greatly simplified complex file/RDD operations in both `GiraphGraphComputer` and `SparkGraphComputer`.

Finally, note that the following low-level/internal classes have been removed: `HadoopLoader` and `HDFSTools`.

See: TINKERPOP-1033, TINKERPOP-1023

#### Gremlin Server Transaction Management

Gremlin Server now has a setting called `strictTransactionManagement`, which forces the user to pass `aliases` for all requests. The aliases are then used to determine which graphs will have their transactions closed for that request. The alternative is to continue with default operations where the transactions of all configured graphs will be closed. It is likely that `strictTransactionManagement` (which is `false` by default so as to be backward compatible with previous versions) will become the future standard mode of operation for Gremlin Server as it provides a more efficient method for transaction management.

See: TINKERPOP-930, Reference Documentation - Considering Transactions

#### Deprecated credentialsDbLocation

The `credentialsDbLocation` setting was a TinkerGraph only configuration option to the `SimpleAuthenticator` for Gremlin Server. It provided the file system location to a "credentials graph" that TinkerGraph would read from a Gryo file at that spot. This setting was only required because TinkerGraph did not support file persistence at the time that `SimpleAuthenticator` was created.

As of 3.1.0-incubating, TinkerGraph received a limited persistence feature that allowed the "credentials graph" location to be specified in the TinkerGraph properties file via `gremlin.tinkergraph.graphLocation` and as such the need for `credentialsDbLocation` was eliminated.

This deprecation is not a breaking change, however users should be encouraged to convert their configurations to use the `gremlin.tinkergraph.graphLocation` as soon as possible, as the deprecated setting will be removed in a future release.

See: TINKERPOP-981, Reference Documentation - Gremlin Server Security

#### TinkerGraph Supports Any I/O

TinkerGraph’s 'gremlin.tinkergraph.graphLocation' configuration setting can now take a fully qualified class name of a `Io.Builder` implementation, which means that custom IO implementations can be used to read and write TinkerGraph instances.

See: TINKERPOP-886

#### Authenticator Method Deprecation

For users who have a custom `Authenticator` implementation for Gremlin Server, there will be a new method present:

    public default SaslNegotiator newSaslNegotiator(final InetAddress remoteAddress)

Implementation of this method is now preferred over the old method with the same name that has no arguments. The old method has been deprecated. This is a non-breaking change as the new method has a default implementation that simply calls the old deprecated method. In this way, existing `Authenticator` implementations will still work.

See: TINKERPOP-995

#### Spark Persistence Updates

Spark RDD persistence is now much safer with a "job server" system that ensures that persisted RDDs are not garbage collected by Spark. With this, the user is provider a `spark` object that enables them to manage persisted RDDs much like the `hdfs` object is used for managing files in HDFS.

Finally, `InputRDD` instance no longer need a `reduceByKey()` postfix as view merges happen prior to writing the `graphRDD`. Note that a `reduceByKey()` postfix will not cause problems if continued, it is simply inefficient and no longer required.

See: TINKERPOP-1023, TINKERPOP-1027

#### Logging

Logging to Gremlin Server and Gremlin Console can now be consistently controlled by the `log4j-server.properties` and `log4j-console.properties` which are in the respective `conf/` directories of the packaged distributions.

See: TINKERPOP-859

#### Gremlin Server Sandboxing

A number of improvements were made to the sandboxing feature of Gremlin Server (more specifically the `GremlinGroovyScriptEngine`). A new base class for sandboxing was introduce with the `AbstractSandboxExtension`, which makes it a bit easier to build white list style sandboxes. A usable implementation of this was also supplied with the `FileSandboxExtension`, which takes a configuration file containing a white list of accessible methods and variables that can be used in scripts. Note that the original `SandboxExtension` has been deprecated in favor of the `AbsstractSandboxExtension` or extending directly from Groovy’s `TypeCheckingDSL`.

See: TINKERPOP-891, Reference Documentation - Script Execution

#### Deprecated supportsAddProperty()

It was realized that `VertexPropertyFeatures.supportsAddProperty()` was effectively a duplicate of `VertexFeatures.supportsMetaProperties()`. As a result, `supportsAddProperty()` was deprecated in favor of the other. If using `supportsAddProperty()`, simply modify that code to instead utilize `supportsMetaProperties()`.

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

#### Graph System Providers

##### Data Types in Tests

There were a number of fixes related to usage of appropriate types in the test suite. There were cases where tests were mixing types, such that a single property key might have two different values. This mixed typing caused problems for some graphs and wasn’t really something TinkerPop was looking to explicitly enforce as a rule of implementing the interfaces.

While the changes should not have been breaking, providers should be aware that improved consistencies in the tests may present opportunities for test failures.

See: TINKERPOP-984, TINKERPOP-990, TINKERPOP-1000

#### Graph Database Providers

##### Custom ClassResolver

For providers who have built custom serializers in Gryo, there is a new feature open that can be considered. A `GryoMapper` can now take a custom Kryo `ClassResolver`, which means that custom types can be coerced to other types during serialization (e.g. a custom identifier could be serialized as a `HashMap`). The advantage to taking this approach is that users will not need to have the provider’s serializers on the client side. They will only need to exist on the server (presuming that the a type is coerced to a type available on the client, of course). The downside is that serialization is then no longer a two way street. For example, a custom `ClassResolver` that coerced a custom identifier to `HashMap` would let the client work with the identifier as a `HashMap`, but the client would then have to send that identifier back to the server as a `HashMap` where it would be recognized as a `HashMap` (not an identifier).

See: TINKERPOP-1064

##### Feature Consistency

There were a number of corrections made around the consistency of `Features` and how they were applied in tests. Corrections fell into two groups of changes:

1. Bugs in the how `Features` were applied to certain tests.

2. Refactoring around the realization that `VertexFeatures.supportsMetaProperties()` is really just a duplicate of features already exposed as `VertexPropertyFeatures.supportsAddProperty()`. `VertexPropertyFeatures.supportsAddProperty()` has been deprecated.

These changes related to "Feature Consistency" open up a number of previously non-executing tests for graphs that did not support meta-properties, so providers should be wary of potential test failure on previously non-executing tests.

See: TINKERPOP-985, TINKERPOP-997, TINKERPOP-998

#### Graph Processor Providers

##### InputRDD and OutputRDD Updates

There are two new methods on the Spark-Gremlin RDD interfaces.

- `InputRDD.readMemoryRDD()`: get a `ComputerResult.memory()` from an RDD.

- `OutputRDD.writeMemoryRDD()`: write a `ComputerResult.memory()` to an RDD.

Note that both these methods have default implementations which simply work with empty RDDs. Most providers will never need to implement these methods as they are specific to file/RDD management for `GraphComputer`. The four classes that implement these methods are `PersistedOutputRDD`, `PersistedInputRDD`, `InputFormatRDD`, and `OutputFormatRDD`. For the interested provider, study the implementations therein to see the purpose of these two new methods.

## TinkerPop 3.1.0

Release Date: November 16, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

Additional upgrade information can be found here:

- TinkerPop 3.0.2

- TinkerPop 3.0.1

### Upgrading for Users

#### Shading Jackson

The Jackson library is now shaded to `gremlin-shaded`, which will allow Jackson to version independently without breaking compatibility with dependent libraries or with those who depend on TinkerPop. The downside is that if a library depends on TinkerPop and uses the Jackson classes, those classes will no longer exist with the standard Jackson package naming. They will have to shifted as follows:

- `org.objenesis` becomes `org.apache.tinkerpop.shaded.objenesis`

- `com.esotericsoftware.minlog` becomes `org.apache.tinkerpop.shaded.minlog`

- `com.fasterxml.jackson` becomes `org.apache.tinkerpop.shaded.jackson`

See: TINKERPOP-835

#### PartitionStrategy and VertexProperty

`PartitionStrategy` now supports partitioning within `VertexProperty`. The `Graph` needs to be able to support meta-properties for this feature to work.

See: TINKERPOP-333

#### Gremlin Server and Epoll

Gremlin Server provides a configuration option to turn on support for Netty native transport on Linux, which has been shown to help improve performance.

See: TINKERPOP-901

#### Rebindings Deprecated

The notion of "rebindings" has been deprecated in favor of the term "aliases". Alias is a better and more intuitive term than rebindings which should make it easier for newcomers to understand what they are for.

See: TINKERPOP-913, Reference Documentation - Aliases

#### Configurable Driver Channelizer

The Gremlin Driver now allows the `Channerlizer` to be supplied as a configuration, which means that custom implementations may be supplied.

See: TINKERPOP-680

#### GraphSON and Strict Option

The `GraphMLReader` now has a `strict` option on the `Builder` so that if a data type for a value is invalid in some way, GraphMLReader will simply skip that problem value. In that way, it is a bit more forgiving than before especially with empty data.

See: TINKERPOP-756

#### Transaction.close() Default Behavior

The default behavior of `Transaction.close()` is to rollback the transaction. This is in contrast to previous versions where the default behavior was commit. Using rollback as the default should be thought of as a like a safer approach to closing where a user must now explicitly call `commit()` to persist their mutations.

See TINKERPOP-805 for more information.

#### ThreadLocal Transaction Settings

The `Transaction.onReadWrite()` and `Transaction.onClose()` settings now need to be set for each thread (if another behavior than the default is desired). For gremlin-server users that may be changing these settings via scripts. If the settings are changed for a sessionless request they will now only apply to that one request. If the settings are changed for an in-session request they will now only apply to all future requests made in the scope of that session.

See TINKERPOP-885

#### Hadoop-Gremlin

- Hadoop1 is no longer supported. Hadoop2 is now the only supported Hadoop version in TinkerPop.

- Spark and Giraph have been split out of Hadoop-Gremlin into their own respective packages (Spark-Gremlin and Giraph-Gremlin).

- The directory where application jars are stored in HDFS is now `hadoop-gremlin-3.5.1-libs`.

  - This versioning is important so that cross-version TinkerPop use does not cause jar conflicts.

See link:https://issues.apache.org/jira/browse/TINKERPOP-616

#### Spark-Gremlin

- Providers that wish to reuse a graphRDD can leverage the new `PersistedInputRDD` and `PersistedOutputRDD`.

  - This allows the graphRDD to avoid serialization into HDFS for reuse. Be sure to enabled persisted `SparkContext` (see documentation).

See link:https://issues.apache.org/jira/browse/TINKERPOP-868, link:https://issues.apache.org/jira/browse/TINKERPOP-925

#### TinkerGraph Serialization

TinkerGraph is serializable over Gryo, which means that it can shipped over the wire from Gremlin Server. This feature can be useful when working with remote subgraphs.

See: TINKERPOP-728

#### Deprecation in TinkerGraph

The `public static String` configurations have been renamed. The old `public static` variables have been deprecated. If the deprecated variables were being used, then convert to the replacements as soon as possible.

See: TINKERPOP-926

#### Deprecation in Gremlin-Groovy

The closure wrappers classes `GFunction`, `GSupplier`, `GConsumer` have been deprecated. In Groovy, a closure can be specified using `as Function` and thus, these wrappers are not needed. Also, the `GremlinExecutor.promoteBindings()` method which was previously deprecated has been removed.

See: TINKERPOP-879, TINKERPOP-897

#### Gephi Traversal Visualization

The process for visualizing a traversal has been simplified. There is no longer a need to "name" steps that will represent visualization points for Gephi. It is possible to just "configure" a `visualTraversal` in the console:

    gremlin> :remote config visualTraversal graph vg

which creates a special `TraversalSource` from `graph` called `vg`. The traversals created from `vg` can be used to `:submit` to Gephi.

See: Reference Documentation - Gephi

#### Alterations to GraphTraversal

There were a number of changes to `GraphTraversal`. Many of the changes came by way of deprecation, but some semantics have changed as well:

- `ConjunctionStrategy` has been renamed to `ConnectiveStrategy` (no other behaviors changed).

- `ConjunctionP` has been renamed to `ConnectiveP` (no other behaviors changed).

- `DedupBijectionStrategy` has been renamed (and made more effective) as `FilterRankingStrategy`.

- The `GraphTraversal` mutation API has change significantly with all previous methods being supported but deprecated.

  - The general pattern used now is `addE('knows').from(select('a')).to(select('b')).property('weight',1.0)`.

- The `GraphTraversal` sack API has changed with all previous methods being supported but deprecated.

  - The old `sack(mult,'weight')` is now `sack(mult).by('weight')`.

- `GroupStep` has been redesigned such that there is now only a key- and value-traversal. No more reduce-traversal.

  - The previous `group()`-methods have been renamed to `groupV3d0()`. To immediately upgrade, rename all your `group()`-calls to `groupV3d0()`.

  - To migrate to the new `group()`-methods, what was `group().by('age').by(outE()).by(sum(local))` is now `group().by('age').by(outE().sum())`.

- There was a bug in `fold()`, where if a bulked traverser was provided, the traverser was only represented once.

  - This bug fix might cause a breaking change to a user query if the non-bulk behavior was being counted on. If so, used `dedup()` prior to `fold()`.

- Both `GraphTraversal().mapKeys()` and `GraphTraversal.mapValues()` has been deprecated.

  - Use `select(keys)` and `select(columns)`. However, note that `select()` will not unroll the keys/values. Thus, `mapKeys()` ⇒ `select(keys).unfold()`.

- The data type of `Operator` enums will now always be the highest common data type of the two given numbers, rather than the data type of the first number, as it’s been before.

#### Aliasing Remotes in the Console

The `:remote` command in Gremlin Console has a new `alias` configuration option. This `alias` option allows specification of a set of key/value alias/binding pairs to apply to the remote. In this way, it becomes possible to refer to a variable on the server as something other than what it is referred to for purpose of the submitted script. For example once a `:remote` is created, this command:

    :remote alias x g

would allow "g" on the server to be referred to as "x".

    :> x.E().label().groupCount()

See: TINKERPOP-914

### Upgrading for Providers

Important | It is recommended that providers also review all the upgrade instructions specified for users. Many of the changes there may prove important for the provider’s implementation.

All providers should be aware that Jackson is now shaded to `gremlin-shaded` and could represent breaking change if there was usage of the dependency by way of TinkerPop, a direct dependency to Jackson may be required on the provider’s side.

#### Graph System Providers

##### GraphStep Alterations

- `GraphStep` is no longer in `sideEffect`-package, but now in `map`-package as traversals support mid-traversal `V()`.

- Traversals now support mid-traversal `V()`-steps. Graph system providers should ensure that a mid-traversal `V()` can leverage any suitable index.

See link:https://issues.apache.org/jira/browse/TINKERPOP-762

##### Decomposition of AbstractTransaction

The `AbstractTransaction` class has been abstracted into two different classes supporting two different modes of operation: `AbstractThreadLocalTransaction` and `AbstractThreadedTransaction`, where the former should be used when supporting `ThreadLocal` transactions and the latter for threaded transactions. Of course, providers may still choose to build their own implementation on `AbstractTransaction` itself or simply implement the `Transaction` interface.

The `AbstractTransaction` gains the following methods to potentially implement (though default implementations are supplied in `AbstractThreadLocalTransaction` and `AbstractThreadedTransaction`):

- `doReadWrite` that should execute the read-write consumer.

- `doClose` that should execute the close consumer.

See: TINKERPOP-765, TINKERPOP-885

##### Transaction.close() Default Behavior

The default behavior for `Transaction.close()` is to rollback the transaction and is enforced by tests, which previously asserted the opposite (i.e. commit on close). These tests have been renamed to suite the new semantics:

- `shouldCommitOnCloseByDefault` became `shouldCommitOnCloseWhenConfigured`

- `shouldRollbackOnCloseWhenConfigured` became `shouldRollbackOnCloseByDefault`

If these tests were referenced in an `OptOut`, then their names should be updated.

See: TINKERPOP-805

##### Graph Traversal Updates

There were numerous changes to the `GraphTraversal` API. Nearly all changes are backwards compatible with respective "deprecated" annotations. Please review the respective updates specified in the "Graph System Users" section.

- `GraphStep` is no longer in `sideEffect` package. Now in `map` package.

- Make sure mid-traversal `GraphStep` calls are folding `HasContainers` in for index-lookups.

- Think about copying `TinkerGraphStepStrategyTest` for your implementation so you know folding is happening correctly.

##### Element Removal

`Element.Exceptions.elementAlreadyRemoved` has been deprecated and test enforcement for consistency have been removed. Providers are free to deal with deleted elements as they see fit.

See: TINKERPOP-297

##### VendorOptimizationStrategy Rename

The `VendorOptimizationStrategy` has been renamed to `ProviderOptimizationStrategy`. This renaming is consistent with revised terminology for what were formerly referred to as "vendors".

See: TINKERPOP-876

##### GraphComputer Updates

`GraphComputer.configure(String key, Object value)` is now a method (with default implementation). This allows the user to specify engine-specific parameters to the underlying OLAP system. These parameters are not intended to be cross engine supported. Moreover, if there are not parameters that can be altered (beyond the standard `GraphComputer` methods), then the provider’s `GraphComputer` implementation should simply return and do nothing.

#### Driver Providers

##### Aliases Parameter

The "rebindings" argument to the "standard" `OpProcessor` has been renamed to "aliases". While "rebindings" is still supported it is recommended that the upgrade to "aliases" be made as soon as possible as support will be removed in the future. Gremlin Server will not accept both parameters at the same time - a request must contain either one parameter or the other if either is supplied.

See: TINKERPOP-913

##### ThreadLocal Transaction Settings

If a driver configures the `Transaction.onReadWrite()` or `Transaction.onClose()` settings, note that these settings no longer apply to all future requests. If the settings are changed for a sessionless request they will only apply to that one request. If the settings are changed from an in-session request they will only apply to all future requests made in the scope of that session.

See: TINKERPOP-885

# TinkerPop 3.0.0

A Gremlin Rāga in 7/16 Time

## TinkerPop 3.0.2

Release Date: October 19, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### BulkLoaderVertexProgram (BLVP)

`BulkLoaderVertexProgram` now supports arbitrary inputs (i addition to `HadoopGraph`, which was already supported in version 3.0.1-incubating). It can now also read from any TP3 enabled graph, like `TinkerGraph` or `Neo4jGraph`.

See: TINKERPOP-319, Reference Documentation - BLVP

#### TinkerGraph

TinkerGraph can now be configured to support persistence, where TinkerGraph will try to load a graph from a specified location and calls to `close()` will save the graph data to that location.

See: TINKERPOP-828, Reference Documentation - TinkerGraph

#### Gremlin Driver and Server

There were a number of fixes to `gremlin-driver` that prevent protocol desynchronization when talking to Gremlin Server.

On the Gremlin Server side, Websocket sub-protocol introduces a new "close" operation to explicitly close sessions. Prior to this change, sessions were closed in a more passive fashion (i.e. session timeout). There were also so bug fixes around the protocol as it pertained to third-party drivers (e.g. python) using JSON for authentication.

See: TINKERPOP-814, TINKERPOP-816, TINKERPOP-817, TINKERPOP-855, TINKERPOP-870, TINKERPOP-877

### Upgrading for Providers

#### Graph Driver Providers

##### Gremlin Server close Operation

It is important to note that this feature of the sub-protocol applies to the `SessionOpProcessor` (i.e. for session-based requests). Prior to this change, there was no way to explicitly close a session. Sessions would get closed by the server after timeout of activity. This new "op" gives drivers the ability to close the session explicitly and as needed.

See: TINKERPOP-849, Reference Documentation - OpProcessor

## TinkerPop 3.0.1

Release Date: September 2, 2015

Please see the changelog for a complete list of all the modifications that are part of this release.

### Upgrading for Users

#### Gremlin Server

Gremlin Server now supports a SASL-based (Simple Authentication and Security Layer) authentication model and a default `SimpleAuthenticator` which implements the `PLAIN` SASL mechanism (i.e. plain text) to authenticate requests. This gives Gremlin Server some basic security capabilities, especially when combined with its built-in SSL feature.

There have also been changes in how global variable bindings in Gremlin Server are established via initialization scripts. The initialization scripts now allow for a `Map` of values that can be returned from those scripts. That `Map` will be used to set global bindings for the server. See this sample script for an example.

See: TINKERPOP-576

#### Neo4j

Problems related to using `:install` to get the Neo4j plugin operating in Gremlin Console on Windows have been resolved.

See: TINKERPOP-804

### Upgrading for Providers

#### Graph System Providers

##### GraphFactoryClass Annotation

Providers can consider the use of the new `GraphFactoryClass` annotation to specify the factory class that `GraphFactory` will use to open a new `Graph` instance. This is an optional feature and will generally help implementations that have an interface extending `Graph`. If that is the case, then this annotation can be used in the following fashion:

    @GraphFactory(MyGraphFactory.class)
    public interface MyGraph extends Graph{
    }

`MyGraphFactory` must contain the static `open` method that is normally expected by `GraphFactory`.

See: TINKERPOP-778

##### GraphProvider.Descriptor Annotation

There was a change that affected providers who implemented `GraphComputer` related tests such as the `ProcessComputerSuite`. If the provider runs those tests, then edit the `GraphProvider` implementation for those suites to include the `GraphProvider.Descriptor` annotation as follows:

    @GraphProvider.Descriptor(computer = GiraphGraphComputer.class)
    public final class HadoopGiraphGraphProvider extends HadoopGraphProvider {

        public GraphTraversalSource traversal(final Graph graph) {
            return GraphTraversalSource.build().engine(ComputerTraversalEngine.build().computer(GiraphGraphComputer.class)).create(graph);
        }
    }

See: TINKERPOP-690 for more information.

##### Semantics of Transaction.close()

There were some adjustments to the test suite with respect to how `Transaction.close()` was being validated. For most providers, this will generally mean checking `OptOut` annotations for test renaming problems. The error that occurs when running the test suite should make it apparent that a test name is incorrect in an `OptOut` if there are issues there.

See: TINKERPOP-764 for more information.

#### Graph Driver Providers

##### Authentication

Gremlin Server now supports SASL-based authentication. By default, Gremlin Server is not configured with authentication turned on and authentication is not required, so existing drivers should still work without any additional change. Drivers should however consider implementing this feature as it is likely that many users will want the security capabilities that it provides.

See: Reference Documentation - Gremlin Server Authentication

# Appendix

## TinkerPop 2.x

This section contains a few notes that reference differences between TinkerPop 2.x and 3.x.

One of the major differences between TinkerPop 2.x and TinkerPop 3.x is that in TinkerPop 3.x, the Java convention of using setters and getters was abandoned in favor of a syntax that is more aligned with the syntax of Gremlin-Groovy in TinkerPop2. Given that Gremlin-Java and Gremlin-Groovy are nearly identical due to the inclusion of lambdas from Java 8, a big effort was made to ensure that both languages were as similar as possible.

In addition, TinkerPop2 and below made a sharp distinction between the various TinkerPop projects: Blueprints, Pipes, Gremlin, Frames, Furnace, and Rexster. With TinkerPop 3.x, all of these projects have been merged and are generally known as Gremlin. Blueprints → Gremlin Structure API : Pipes → `GraphTraversal` : Frames → `Traversal` : Furnace → `GraphComputer` and `VertexProgram` : Rexster → GremlinServer.

### GraphML Format

GraphML was a supported format in TinkerPop 2.x, but there were several issues that made it inconsistent with the specification that were corrected for 3.x. As a result, attempting to read a GraphML file generated by 2.x with the 3.x `GraphMLReader` will result in error. To help with this problem, an XSLT file is provided as a resource in `gremlin-core` which will transform 2.x GraphML to 3.x GraphML. It can be used as follows:

    import javax.xml.parsers.DocumentBuilderFactory;
    import javax.xml.transform.TransformerFactory;
    import javax.xml.transform.dom.DOMSource;
    import javax.xml.transform.stream.StreamSource;
    import javax.xml.transform.stream.StreamResult;

    InputStream stylesheet = Thread.currentThread().getContextClassLoader().getResourceAsStream("tp2-to-tp3-graphml.xslt");
    File datafile = new File('/tmp/tp2-graphml.xml');
    File outfile = new File('/tmp/tp3-graphml.xml');

    TransformerFactory tFactory = TransformerFactory.newInstance();
    StreamSource stylesource = new StreamSource(stylesheet);
    Transformer transformer = tFactory.newTransformer(stylesource);

    StreamSource source = new StreamSource(datafile);
    StreamResult result = new StreamResult(new FileWriter(outfile));
    transformer.transform(source, result);

### TinkerPop2 Data Migration

For those using TinkerPop 2.x, migrating to TinkerPop 3.x will mean a number of programming changes, but may also require a migration of the data depending on the graph implementation. For example, trying to open `TinkerGraph` data from TinkerPop 2.x with TinkerPop 3.x code will not work, however opening a TinkerPop2 `Neo4jGraph` with a TinkerPop 3.x `Neo4jGraph` should work provided there aren’t Neo4j version compatibility mismatches preventing the read.

If such a situation arises that a particular TinkerPop 2.x `Graph` can not be read by TinkerPop 3.x, a "legacy" data migration approach exists. The migration involves writing the TinkerPop2 `Graph` to GraphSON, then reading it to TinkerPop 3.x with the `LegacyGraphSONReader` (a limited implementation of the `GraphReader` interface).

The following represents an example migration of the "classic" toy graph. In this example, the "classic" graph is saved to GraphSON using TinkerPop 2.x.

    gremlin> Gremlin.version()
    ==>2.5.z
    gremlin> graph = TinkerGraphFactory.createTinkerGraph()
    ==>tinkergraph[vertices:6 edges:6]
    gremlin> GraphSONWriter.outputGraph(graph,'/tmp/tp2.json',GraphSONMode.EXTENDED)
    ==>null

The above console session uses the `gremlin-groovy` distribution from TinkerPop2. It is important to generate the `tp2.json` file using the `EXTENDED` mode as it will include data types when necessary which will help limit "lossiness" on the TinkerPop 3.x side when imported. Once `tp2.json` is created, it can then be imported to a TinkerPop 3.x `Graph`.

    gremlin> Gremlin.version()
    ==>3.5.1
    gremlin> graph = TinkerGraph.open()
    ==>tinkergraph[vertices:0 edges:0]
    gremlin> r = LegacyGraphSONReader.build().create()
    ==>org.apache.tinkerpop.gremlin.structure.io.graphson.LegacyGraphSONReader@64337702
    gremlin> r.readGraph(new FileInputStream('/tmp/tp2.json'), graph)
    ==>null
    gremlin> g = graph.traversal()
    ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
    gremlin> g.E()
    ==>e[11][4-created->3]
    ==>e[12][6-created->3]
    ==>e[7][1-knows->2]
    ==>e[8][1-knows->4]
    ==>e[9][1-created->3]
    ==>e[10][4-created->5]