/**
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.hadoop.hbase.regionserver.wal;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ImmutableByteArray;
  
  /**
   * Accounting of sequence ids per region and then by column family. So we can our accounting
   * current, call startCacheFlush and then finishedCacheFlush or abortCacheFlush so this instance can
   * keep abreast of the state of sequence id persistence. Also call update per append.
   * <p>
   * For the implementation, we assume that all the {@code encodedRegionName} passed in is gotten by
   * {@link HRegionInfo#getEncodedNameAsBytes()}. So it is safe to use it as a hash key. And for
   * family name, we use {@link ImmutableByteArray} as key. This is because hash based map is much
   * faster than RBTree or CSLM and here we are on the critical write path. See HBASE-16278 for more
   * details.
   */
  @InterfaceAudience.Private
  class SequenceIdAccounting {
  
    private static final Log LOG = LogFactory.getLog(SequenceIdAccounting.class);
    /**
     * This lock ties all operations on {@link SequenceIdAccounting#flushingSequenceIds} and
     * {@link #lowestUnflushedSequenceIds} Maps. {@link #lowestUnflushedSequenceIds} has the
     * lowest outstanding sequence ids EXCEPT when flushing. When we flush, the current
     * lowest set for the region/column family are moved (atomically because of this lock) to
     * {@link #flushingSequenceIds}.
     * 
     * <p>The two Maps are tied by this locking object EXCEPT when we go to update the lowest
     * entry; see {@link #lowest(byte[], Set, Long)}. In here is a putIfAbsent call on
     * {@link #lowestUnflushedSequenceIds}. In this latter case, we will add this lowest
     * sequence id if we find that there is no entry for the current column family. There will be no
     * entry only if we just came up OR we have moved aside current set of lowest sequence ids
     * because the current set are being flushed (by putting them into {@link #flushingSequenceIds}).
     * This is how we pick up the next 'lowest' sequence id per region per column family to be used
     * figuring what is in the next flush.
     */
    private final Object tieLock = new Object();
  
    /**
     * Map of encoded region names and family names to their OLDEST -- i.e. their first,
     * the longest-lived, their 'earliest', the 'lowest' -- sequence id.
     *
     * <p>When we flush, the current lowest sequence ids get cleared and added to
     * {@link #flushingSequenceIds}. The next append that comes in, is then added
     * here to {@link #lowestUnflushedSequenceIds} as the next lowest sequenceid.
     *
     * <p>If flush fails, currently server is aborted so no need to restore previous sequence ids.
     * <p>Needs to be concurrent Maps because we use putIfAbsent updating oldest.
     */
    private final ConcurrentMap<byte[], ConcurrentMap<ImmutableByteArray, Long>>
      lowestUnflushedSequenceIds = new ConcurrentHashMap<>();
  
    /**
     * Map of encoded region names and family names to their lowest or OLDEST sequence/edit id
     * currently being flushed out to hfiles. Entries are moved here from
     * {@link #lowestUnflushedSequenceIds} while the lock {@link #tieLock} is held
     * (so movement between the Maps is atomic).
     */
    private final Map<byte[], Map<ImmutableByteArray, Long>> flushingSequenceIds = new HashMap<>();
  
   /**
    * Map of region encoded names to the latest/highest region sequence id.  Updated on each
    * call to append.
    * <p>
    * This map uses byte[] as the key, and uses reference equality. It works in our use case as we
    * use {@link HRegionInfo#getEncodedNameAsBytes()} as keys. For a given region, it always returns
    * the same array.
    */
   private Map<byte[], Long> highestSequenceIds = new HashMap<>();
 
   /**
    * Returns the lowest unflushed sequence id for the region.
    * @param encodedRegionName
    * @return Lowest outstanding unflushed sequenceid for <code>encodedRegionName</code>. Will
    * return {@link HConstants#NO_SEQNUM} when none.
    */
   long getLowestSequenceId(final byte[] encodedRegionName) {
     synchronized (this.tieLock) {
       Map<?, Long> m = this.flushingSequenceIds.get(encodedRegionName);
       long flushingLowest = m != null ? getLowestSequenceId(m) : Long.MAX_VALUE;
       m = this.lowestUnflushedSequenceIds.get(encodedRegionName);
       long unflushedLowest = m != null ? getLowestSequenceId(m) : HConstants.NO_SEQNUM;
       return Math.min(flushingLowest, unflushedLowest);
     }
   }
 
   /**
    * @param encodedRegionName
    * @param familyName
    * @return Lowest outstanding unflushed sequenceid for <code>encodedRegionname</code> and
    *         <code>familyName</code>. Returned sequenceid may be for an edit currently being
    *         flushed.
    */
   long getLowestSequenceId(final byte[] encodedRegionName, final byte[] familyName) {
     ImmutableByteArray familyNameWrapper = ImmutableByteArray.wrap(familyName);
     synchronized (this.tieLock) {
       Map<ImmutableByteArray, Long> m = this.flushingSequenceIds.get(encodedRegionName);
       if (m != null) {
         Long lowest = m.get(familyNameWrapper);
         if (lowest != null) {
           return lowest;
         }
       }
       m = this.lowestUnflushedSequenceIds.get(encodedRegionName);
       if (m != null) {
         Long lowest = m.get(familyNameWrapper);
         if (lowest != null) {
           return lowest;
         }
       }
     }
     return HConstants.NO_SEQNUM;
   }
 
   /**
    * Reset the accounting of highest sequenceid by regionname.
    * @return Return the previous accounting Map of regions to the last sequence id written into
    * each.
    */
   Map<byte[], Long> resetHighest() {
     Map<byte[], Long> old = this.highestSequenceIds;
     this.highestSequenceIds = new HashMap<byte[], Long>();
     return old;
   }
 
   /**
    * We've been passed a new sequenceid for the region. Set it as highest seen for this region and
    * if we are to record oldest, or lowest sequenceids, save it as oldest seen if nothing
    * currently older.
    * @param encodedRegionName
    * @param families
    * @param sequenceid
    * @param lowest Whether to keep running account of oldest sequence id.
    */
   void update(byte[] encodedRegionName, Set<byte[]> families, long sequenceid,
       final boolean lowest) {
     Long l = Long.valueOf(sequenceid);
     this.highestSequenceIds.put(encodedRegionName, l);
     if (lowest) {
       ConcurrentMap<ImmutableByteArray, Long> m = getOrCreateLowestSequenceIds(encodedRegionName);
       for (byte[] familyName : families) {
         m.putIfAbsent(ImmutableByteArray.wrap(familyName), l);
       }
     }
   }
 
   ConcurrentMap<ImmutableByteArray, Long> getOrCreateLowestSequenceIds(byte[] encodedRegionName) {
     // Intentionally, this access is done outside of this.regionSequenceIdLock. Done per append.
     ConcurrentMap<ImmutableByteArray, Long> m = this.lowestUnflushedSequenceIds
         .get(encodedRegionName);
     if (m != null) {
       return m;
     }
     m = new ConcurrentHashMap<>();
     // Another thread may have added it ahead of us.
     ConcurrentMap<ImmutableByteArray, Long> alreadyPut = this.lowestUnflushedSequenceIds
         .putIfAbsent(encodedRegionName, m);
     return alreadyPut == null ? m : alreadyPut;
   }
 
   /**
    * @param sequenceids Map to search for lowest value.
    * @return Lowest value found in <code>sequenceids</code>.
    */
   private static long getLowestSequenceId(Map<?, Long> sequenceids) {
     long lowest = HConstants.NO_SEQNUM;
     for (Long sid: sequenceids.values()) {
       if (lowest == HConstants.NO_SEQNUM || sid.longValue() < lowest) {
         lowest = sid.longValue();
       }
     }
     return lowest;
   }
 
   /**
    * @param src
    * @return New Map that has same keys as <code>src</code> but instead of a Map for a value, it
    *         instead has found the smallest sequence id and it returns that as the value instead.
    */
   private <T extends Map<?, Long>> Map<byte[], Long> flattenToLowestSequenceId(Map<byte[], T> src) {
     if (src == null || src.isEmpty()) {
       return null;
     }
     Map<byte[], Long> tgt = new HashMap<>();
     for (Map.Entry<byte[], T> entry : src.entrySet()) {
       long lowestSeqId = getLowestSequenceId(entry.getValue());
       if (lowestSeqId != HConstants.NO_SEQNUM) {
         tgt.put(entry.getKey(), lowestSeqId);
       }
     }
     return tgt;
   }
 
   /**
    * @param encodedRegionName Region to flush.
    * @param families Families to flush. May be a subset of all families in the region.
    * @return Returns {@link HConstants#NO_SEQNUM} if we are flushing the whole region OR if
    * we are flushing a subset of all families but there are no edits in those families not
    * being flushed; in other words, this is effectively same as a flush of all of the region
    * though we were passed a subset of regions. Otherwise, it returns the sequence id of the
    * oldest/lowest outstanding edit.
    */
   Long startCacheFlush(final byte[] encodedRegionName, final Set<byte[]> families) {
     Map<ImmutableByteArray, Long> oldSequenceIds = null;
     Long lowestUnflushedInRegion = HConstants.NO_SEQNUM;
     synchronized (tieLock) {
       Map<ImmutableByteArray, Long> m = this.lowestUnflushedSequenceIds.get(encodedRegionName);
       if (m != null) {
         // NOTE: Removal from this.lowestUnflushedSequenceIds must be done in controlled
         // circumstance because another concurrent thread now may add sequenceids for this family
         // (see above in getOrCreateLowestSequenceId). Make sure you are ok with this. Usually it
         // is fine because updates are blocked when this method is called. Make sure!!!
         for (byte[] familyName : families) {
           ImmutableByteArray familyNameWrapper = ImmutableByteArray.wrap(familyName);
           Long seqId = m.remove(familyNameWrapper);
           if (seqId != null) {
             if (oldSequenceIds == null) {
               oldSequenceIds = new HashMap<>();
             }
             oldSequenceIds.put(familyNameWrapper, seqId);
           }
         }
         if (oldSequenceIds != null && !oldSequenceIds.isEmpty()) {
           if (this.flushingSequenceIds.put(encodedRegionName, oldSequenceIds) != null) {
             LOG.warn("Flushing Map not cleaned up for " + Bytes.toString(encodedRegionName) +
               ", sequenceid=" + oldSequenceIds);
           }
         }
         if (m.isEmpty()) {
           // Remove it otherwise it will be in oldestUnflushedStoreSequenceIds for ever
           // even if the region is already moved to other server.
           // Do not worry about data racing, we held write lock of region when calling
           // startCacheFlush, so no one can add value to the map we removed.
           this.lowestUnflushedSequenceIds.remove(encodedRegionName);
         } else {
           // Flushing a subset of the region families. Return the sequence id of the oldest entry.
           lowestUnflushedInRegion = Collections.min(m.values());
         }
       }
     }
     // Do this check outside lock.
     if (oldSequenceIds != null && oldSequenceIds.isEmpty()) {
       // TODO: if we have no oldStoreSeqNum, and WAL is not disabled, presumably either
       // the region is already flushing (which would make this call invalid), or there
       // were no appends after last flush, so why are we starting flush? Maybe we should
       // assert not empty. Less rigorous, but safer, alternative is telling the caller to stop.
       // For now preserve old logic.
       LOG.warn("Couldn't find oldest sequenceid for " + Bytes.toString(encodedRegionName));
     }
     return lowestUnflushedInRegion;
   }
 
   void completeCacheFlush(final byte[] encodedRegionName) {
     synchronized (tieLock) {
       this.flushingSequenceIds.remove(encodedRegionName);
     }
   }
 
   void abortCacheFlush(final byte[] encodedRegionName) {
     // Method is called when we are crashing down because failed write flush AND it is called
     // if we fail prepare. The below is for the fail prepare case; we restore the old sequence ids.
     Map<ImmutableByteArray, Long> flushing = null;
     Map<ImmutableByteArray, Long> tmpMap = new HashMap<>();
     // Here we are moving sequenceids from flushing back to unflushed; doing opposite of what
     // happened in startCacheFlush. During prepare phase, we have update lock on the region so
     // no edits should be coming in via append.
     synchronized (tieLock) {
       flushing = this.flushingSequenceIds.remove(encodedRegionName);
       if (flushing != null) {
         Map<ImmutableByteArray, Long> unflushed = getOrCreateLowestSequenceIds(encodedRegionName);
         for (Map.Entry<ImmutableByteArray, Long> e: flushing.entrySet()) {
           // Set into unflushed the 'old' oldest sequenceid and if any value in flushed with this
           // value, it will now be in tmpMap.
           tmpMap.put(e.getKey(), unflushed.put(e.getKey(), e.getValue()));
         }
       }
     }
 
     // Here we are doing some 'test' to see if edits are going in out of order. What is it for?
     // Carried over from old code.
     if (flushing != null) {
       for (Map.Entry<ImmutableByteArray, Long> e : flushing.entrySet()) {
         Long currentId = tmpMap.get(e.getKey());
         if (currentId != null && currentId.longValue() <= e.getValue().longValue()) {
           String errorStr = Bytes.toString(encodedRegionName) + " family "
               + e.getKey().toStringUtf8() + " acquired edits out of order current memstore seq="
               + currentId + ", previous oldest unflushed id=" + e.getValue();
           LOG.error(errorStr);
           Runtime.getRuntime().halt(1);
         }
       }
     }
   }
 
   /**
    * See if passed <code>sequenceids</code> are lower -- i.e. earlier -- than any outstanding
    * sequenceids, sequenceids we are holding on to in this accounting instance.
    * @param sequenceids Keyed by encoded region name. Cannot be null (doesn't make sense for it to
    *          be null).
    * @return true if all sequenceids are lower, older than, the old sequenceids in this instance.
    */
   boolean areAllLower(Map<byte[], Long> sequenceids) {
     Map<byte[], Long> flushing = null;
     Map<byte[], Long> unflushed = null;
     synchronized (this.tieLock) {
       // Get a flattened -- only the oldest sequenceid -- copy of current flushing and unflushed
       // data structures to use in tests below.
       flushing = flattenToLowestSequenceId(this.flushingSequenceIds);
       unflushed = flattenToLowestSequenceId(this.lowestUnflushedSequenceIds);
     }
     for (Map.Entry<byte[], Long> e : sequenceids.entrySet()) {
       long oldestFlushing = Long.MAX_VALUE;
       long oldestUnflushed = Long.MAX_VALUE;
       if (flushing != null && flushing.containsKey(e.getKey())) {
         oldestFlushing = flushing.get(e.getKey());
       }
       if (unflushed != null && unflushed.containsKey(e.getKey())) {
         oldestUnflushed = unflushed.get(e.getKey());
       }
       long min = Math.min(oldestFlushing, oldestUnflushed);
       if (min <= e.getValue()) {
         return false;
       }
     }
     return true;
   }
 
   /**
    * Iterates over the given Map and compares sequence ids with corresponding entries in
    * {@link #oldestUnflushedRegionSequenceIds}. If a region in
    * {@link #oldestUnflushedRegionSequenceIds} has a sequence id less than that passed in
    * <code>sequenceids</code> then return it.
    * @param sequenceids Sequenceids keyed by encoded region name.
    * @return regions found in this instance with sequence ids less than those passed in.
    */
   byte[][] findLower(Map<byte[], Long> sequenceids) {
     List<byte[]> toFlush = null;
     // Keeping the old behavior of iterating unflushedSeqNums under oldestSeqNumsLock.
     synchronized (tieLock) {
       for (Map.Entry<byte[], Long> e : sequenceids.entrySet()) {
         Map<ImmutableByteArray, Long> m = this.lowestUnflushedSequenceIds.get(e.getKey());
         if (m == null) {
           continue;
         }
         // The lowest sequence id outstanding for this region.
         long lowest = getLowestSequenceId(m);
         if (lowest != HConstants.NO_SEQNUM && lowest <= e.getValue()) {
           if (toFlush == null) {
             toFlush = new ArrayList<byte[]>();
           }
           toFlush.add(e.getKey());
         }
       }
     }
     return toFlush == null ? null : toFlush.toArray(new byte[0][]);
   }
 }