/*
    * 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.io.hfile;
  
  import java.io.DataInput;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.CellUtil;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.KeyValue.KVComparator;
  import org.apache.hadoop.hbase.NoTagsKeyValue;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.fs.HFileSystem;
  import org.apache.hadoop.hbase.io.FSDataInputStreamWrapper;
  import org.apache.hadoop.hbase.io.encoding.DataBlockEncoder;
  import org.apache.hadoop.hbase.io.encoding.DataBlockEncoding;
  import org.apache.hadoop.hbase.io.encoding.HFileBlockDecodingContext;
  import org.apache.hadoop.hbase.io.hfile.HFile.FileInfo;
  import org.apache.hadoop.hbase.regionserver.KeyValueScanner;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.IdLock;
  import org.apache.hadoop.io.WritableUtils;
  import org.apache.htrace.Trace;
  import org.apache.htrace.TraceScope;
  
  /**
   * {@link HFile} reader for version 2.
   */
  @InterfaceAudience.Private
  public class HFileReaderV2 extends AbstractHFileReader {
  
    private static final Log LOG = LogFactory.getLog(HFileReaderV2.class);
  
    /** Minor versions in HFile V2 starting with this number have hbase checksums */
    public static final int MINOR_VERSION_WITH_CHECKSUM = 1;
    /** In HFile V2 minor version that does not support checksums */
    public static final int MINOR_VERSION_NO_CHECKSUM = 0;
  
    /** HFile minor version that introduced pbuf filetrailer */
    public static final int PBUF_TRAILER_MINOR_VERSION = 2;
  
    /**
     * The size of a (key length, value length) tuple that prefixes each entry in
     * a data block.
     */
    public final static int KEY_VALUE_LEN_SIZE = 2 * Bytes.SIZEOF_INT;
  
    private boolean includesMemstoreTS = false;
    protected boolean decodeMemstoreTS = false;
  
    protected boolean shouldIncludeMemstoreTS() {
      return includesMemstoreTS;
    }
  
    /** Filesystem-level block reader. */
    private HFileBlock.FSReader fsBlockReader;
  
    /**
     * A "sparse lock" implementation allowing to lock on a particular block
     * identified by offset. The purpose of this is to avoid two clients loading
     * the same block, and have all but one client wait to get the block from the
     * cache.
     */
    private IdLock offsetLock = new IdLock();
  
    /**
     * Blocks read from the load-on-open section, excluding data root index, meta
     * index, and file info.
     */
    private List<HFileBlock> loadOnOpenBlocks = new ArrayList<HFileBlock>();
  
    /** Minimum minor version supported by this HFile format */
    static final int MIN_MINOR_VERSION = 0;
  
    /** Maximum minor version supported by this HFile format */
   // We went to version 2 when we moved to pb'ing fileinfo and the trailer on
   // the file. This version can read Writables version 1.
   static final int MAX_MINOR_VERSION = 3;
 
   /** Minor versions starting with this number have faked index key */
   static final int MINOR_VERSION_WITH_FAKED_KEY = 3;
 
   HFileContext hfileContext;
 
   /**
    * Opens a HFile. You must load the index before you can use it by calling
    * {@link #loadFileInfo()}.
    *
    * @param path Path to HFile.
    * @param trailer File trailer.
    * @param fsdis input stream.
    * @param size Length of the stream.
    * @param cacheConf Cache configuration.
    * @param hfs
    * @param conf
    */
   public HFileReaderV2(final Path path, final FixedFileTrailer trailer,
       final FSDataInputStreamWrapper fsdis, final long size, final CacheConfig cacheConf,
       final HFileSystem hfs, final Configuration conf) throws IOException {
     super(path, trailer, size, cacheConf, hfs, conf);
     this.conf = conf;
     trailer.expectMajorVersion(getMajorVersion());
     validateMinorVersion(path, trailer.getMinorVersion());
     this.hfileContext = createHFileContext(fsdis, fileSize, hfs, path, trailer);
     HFileBlock.FSReaderImpl fsBlockReaderV2 =
       new HFileBlock.FSReaderImpl(fsdis, fileSize, hfs, path, hfileContext);
     this.fsBlockReader = fsBlockReaderV2; // upcast
 
     try {
       // Comparator class name is stored in the trailer in version 2.
       comparator = trailer.createComparator();
       dataBlockIndexReader = new HFileBlockIndex.BlockIndexReader(comparator,
         trailer.getNumDataIndexLevels(), this);
       metaBlockIndexReader = new HFileBlockIndex.BlockIndexReader(
         KeyValue.RAW_COMPARATOR, 1);
 
       // Parse load-on-open data.
 
       HFileBlock.BlockIterator blockIter = fsBlockReaderV2.blockRange(
         trailer.getLoadOnOpenDataOffset(),
         fileSize - trailer.getTrailerSize());
 
       // Data index. We also read statistics about the block index written after
       // the root level.
       dataBlockIndexReader.readMultiLevelIndexRoot(
         blockIter.nextBlockWithBlockType(BlockType.ROOT_INDEX),
         trailer.getDataIndexCount());
 
       // Meta index.
       metaBlockIndexReader.readRootIndex(
         blockIter.nextBlockWithBlockType(BlockType.ROOT_INDEX),
         trailer.getMetaIndexCount());
 
       // File info
       fileInfo = new FileInfo();
       fileInfo.read(blockIter.nextBlockWithBlockType(BlockType.FILE_INFO).getByteStream());
       byte[] creationTimeBytes = fileInfo.get(FileInfo.CREATE_TIME_TS);
       this.hfileContext.setFileCreateTime(creationTimeBytes == null? 0:
         Bytes.toLong(creationTimeBytes));
       lastKey = fileInfo.get(FileInfo.LASTKEY);
       avgKeyLen = Bytes.toInt(fileInfo.get(FileInfo.AVG_KEY_LEN));
       avgValueLen = Bytes.toInt(fileInfo.get(FileInfo.AVG_VALUE_LEN));
       byte [] keyValueFormatVersion =
         fileInfo.get(HFileWriterV2.KEY_VALUE_VERSION);
       includesMemstoreTS = keyValueFormatVersion != null &&
         Bytes.toInt(keyValueFormatVersion) ==
           HFileWriterV2.KEY_VALUE_VER_WITH_MEMSTORE;
       fsBlockReaderV2.setIncludesMemstoreTS(includesMemstoreTS);
       if (includesMemstoreTS) {
         decodeMemstoreTS = Bytes.toLong(fileInfo.get(HFileWriterV2.MAX_MEMSTORE_TS_KEY)) > 0;
       }
 
       // Read data block encoding algorithm name from file info.
       dataBlockEncoder = HFileDataBlockEncoderImpl.createFromFileInfo(fileInfo);
       fsBlockReaderV2.setDataBlockEncoder(dataBlockEncoder);
 
       // Store all other load-on-open blocks for further consumption.
       HFileBlock b;
       while ((b = blockIter.nextBlock()) != null) {
         loadOnOpenBlocks.add(b);
       }
       // close the block reader
       fsdis.unbuffer();
     } catch (Throwable t) {
       fsBlockReaderV2.closeStreams();
       throw new CorruptHFileException("Problem reading data index and meta index from file "
         + path, t);
     }
 
     // Prefetch file blocks upon open if requested
     if (cacheConf.shouldPrefetchOnOpen()) {
       PrefetchExecutor.request(path, new Runnable() {
         public void run() {
           long offset = 0;
           long end = 0;
           try {
             end = getTrailer().getLoadOnOpenDataOffset();
             HFileBlock prevBlock = null;
             if (LOG.isTraceEnabled()) {
               LOG.trace("Prefetch start " + getPathOffsetEndStr(path, offset, end));
             }
             while (offset < end) {
               if (Thread.interrupted()) {
                 break;
               }
               // Perhaps we got our block from cache? Unlikely as this may be, if it happens, then
               // the internal-to-hfileblock thread local which holds the overread that gets the
               // next header, will not have happened...so, pass in the onDiskSize gotten from the
               // cached block. This 'optimization' triggers extremely rarely I'd say.
               long onDiskSize = prevBlock != null? prevBlock.getNextBlockOnDiskSize(): -1;
               HFileBlock block = readBlock(offset, onDiskSize, true, false, false, false,
                 null, null);
               prevBlock = block;
               offset += block.getOnDiskSizeWithHeader();
             }
           } catch (IOException e) {
             // IOExceptions are probably due to region closes (relocation, etc.)
             if (LOG.isTraceEnabled()) {
               LOG.trace("Prefetch " + getPathOffsetEndStr(path, offset, end), e);
             }
           } catch (NullPointerException e) {
             LOG.warn("Stream moved/closed or prefetch cancelled?" +
                 getPathOffsetEndStr(path, offset, end), e);
           } catch (Exception e) {
             // Other exceptions are interesting
             LOG.warn("Prefetch " + getPathOffsetEndStr(path, offset, end), e);
           } finally {
             PrefetchExecutor.complete(path);
           }
         }
       });
     }
   }
 
   protected HFileContext createHFileContext(FSDataInputStreamWrapper fsdis, long fileSize,
       HFileSystem hfs, Path path, FixedFileTrailer trailer) throws IOException {
     return new HFileContextBuilder()
       .withIncludesMvcc(this.includesMemstoreTS)
       .withCompression(this.compressAlgo)
       .withHBaseCheckSum(trailer.getMinorVersion() >= MINOR_VERSION_WITH_CHECKSUM)
       .build();
   }
 
   private static String getPathOffsetEndStr(final Path path, final long offset, final long end) {
     return "path=" + path.toString() + ", offset=" + offset + ", end=" + end;
   }
 
   /**
    * Create a Scanner on this file. No seeks or reads are done on creation. Call
    * {@link HFileScanner#seekTo(byte[])} to position an start the read. There is
    * nothing to clean up in a Scanner. Letting go of your references to the
    * scanner is sufficient.
    *
    * @param cacheBlocks True if we should cache blocks read in by this scanner.
    * @param pread Use positional read rather than seek+read if true (pread is
    *          better for random reads, seek+read is better scanning).
    * @param isCompaction is scanner being used for a compaction?
    * @return Scanner on this file.
    */
    @Override
    public HFileScanner getScanner(boolean cacheBlocks, final boolean pread,
       final boolean isCompaction) {
     if (dataBlockEncoder.useEncodedScanner()) {
       return new EncodedScannerV2(this, cacheBlocks, pread, isCompaction,
           hfileContext);
     }
 
     return new ScannerV2(this, cacheBlocks, pread, isCompaction);
   }
 
   /**
    * Retrieve block from cache. Validates the retrieved block's type vs {@code expectedBlockType}
    * and its encoding vs. {@code expectedDataBlockEncoding}. Unpacks the block as necessary.
    */
    private HFileBlock getCachedBlock(BlockCacheKey cacheKey, boolean cacheBlock, boolean useLock,
        boolean isCompaction, boolean updateCacheMetrics, BlockType expectedBlockType,
        DataBlockEncoding expectedDataBlockEncoding) throws IOException {
      // Check cache for block. If found return.
      if (cacheConf.isBlockCacheEnabled()) {
        BlockCache cache = cacheConf.getBlockCache();
        HFileBlock cachedBlock = (HFileBlock) cache.getBlock(cacheKey, cacheBlock, useLock,
          updateCacheMetrics);
        if (cachedBlock != null) {
          if (cacheConf.shouldCacheCompressed(cachedBlock.getBlockType().getCategory())) {
            cachedBlock = cachedBlock.unpack(hfileContext, fsBlockReader);
          }
          validateBlockType(cachedBlock, expectedBlockType);
 
          if (expectedDataBlockEncoding == null) {
            return cachedBlock;
          }
          DataBlockEncoding actualDataBlockEncoding =
                  cachedBlock.getDataBlockEncoding();
          // Block types other than data blocks always have
          // DataBlockEncoding.NONE. To avoid false negative cache misses, only
          // perform this check if cached block is a data block.
          if (cachedBlock.getBlockType().isData() &&
                  !actualDataBlockEncoding.equals(expectedDataBlockEncoding)) {
            // This mismatch may happen if a ScannerV2, which is used for say a
            // compaction, tries to read an encoded block from the block cache.
            // The reverse might happen when an EncodedScannerV2 tries to read
            // un-encoded blocks which were cached earlier.
            //
            // Because returning a data block with an implicit BlockType mismatch
            // will cause the requesting scanner to throw a disk read should be
            // forced here. This will potentially cause a significant number of
            // cache misses, so update so we should keep track of this as it might
            // justify the work on a CompoundScannerV2.
            if (!expectedDataBlockEncoding.equals(DataBlockEncoding.NONE) &&
                    !actualDataBlockEncoding.equals(DataBlockEncoding.NONE)) {
              // If the block is encoded but the encoding does not match the
              // expected encoding it is likely the encoding was changed but the
              // block was not yet evicted. Evictions on file close happen async
              // so blocks with the old encoding still linger in cache for some
              // period of time. This event should be rare as it only happens on
              // schema definition change.
              LOG.info("Evicting cached block with key " + cacheKey +
                      " because of a data block encoding mismatch" +
                      "; expected: " + expectedDataBlockEncoding +
                      ", actual: " + actualDataBlockEncoding);
              cache.evictBlock(cacheKey);
            }
            return null;
          }
          return cachedBlock;
        }
      }
      return null;
    }
   /**
    * @param metaBlockName
    * @param cacheBlock Add block to cache, if found
    * @return block wrapped in a ByteBuffer, with header skipped
    * @throws IOException
    */
   @Override
   public ByteBuffer getMetaBlock(String metaBlockName, boolean cacheBlock)
       throws IOException {
     if (trailer.getMetaIndexCount() == 0) {
       return null; // there are no meta blocks
     }
     if (metaBlockIndexReader == null) {
       throw new IOException("Meta index not loaded");
     }
 
     byte[] mbname = Bytes.toBytes(metaBlockName);
     int block = metaBlockIndexReader.rootBlockContainingKey(mbname,
         0, mbname.length);
     if (block == -1)
       return null;
     long blockSize = metaBlockIndexReader.getRootBlockDataSize(block);
 
     // Per meta key from any given file, synchronize reads for said block. This
     // is OK to do for meta blocks because the meta block index is always
     // single-level.
     synchronized (metaBlockIndexReader.getRootBlockKey(block)) {
       // Check cache for block. If found return.
       long metaBlockOffset = metaBlockIndexReader.getRootBlockOffset(block);
       BlockCacheKey cacheKey = new BlockCacheKey(name, metaBlockOffset,
         this.isPrimaryReplicaReader(), BlockType.META);
 
       cacheBlock &= cacheConf.shouldCacheDataOnRead();
       if (cacheConf.isBlockCacheEnabled()) {
         HFileBlock cachedBlock = getCachedBlock(cacheKey, cacheBlock, false, true, true,
           BlockType.META, null);
         if (cachedBlock != null) {
           assert cachedBlock.isUnpacked() : "Packed block leak.";
           // Return a distinct 'shallow copy' of the block,
           // so pos does not get messed by the scanner
           return cachedBlock.getBufferWithoutHeader();
         }
         // Cache Miss, please load.
       }
 
       HFileBlock metaBlock = fsBlockReader.readBlockData(metaBlockOffset,
           blockSize, true, false).unpack(hfileContext, fsBlockReader);
 
       // Cache the block
       if (cacheBlock) {
         cacheConf.getBlockCache().cacheBlock(cacheKey, metaBlock,
             cacheConf.isInMemory(), this.cacheConf.isCacheDataInL1());
       }
 
       return metaBlock.getBufferWithoutHeader();
     }
   }
 
   @Override
   public HFileBlock readBlock(long dataBlockOffset, long onDiskBlockSize,
       final boolean cacheBlock, boolean pread, final boolean isCompaction,
       boolean updateCacheMetrics, BlockType expectedBlockType,
       DataBlockEncoding expectedDataBlockEncoding)
       throws IOException {
     if (dataBlockIndexReader == null) {
       throw new IOException("Block index not loaded");
     }
     long trailerOffset = trailer.getLoadOnOpenDataOffset();
     if (dataBlockOffset < 0 || dataBlockOffset >= trailerOffset) {
       throw new IOException("Requested block is out of range: " + dataBlockOffset +
         ", lastDataBlockOffset: " + trailer.getLastDataBlockOffset() +
         ", trailer.getLoadOnOpenDataOffset: " + trailerOffset);
     }
 
     // For any given block from any given file, synchronize reads for said block.
     // Without a cache, this synchronizing is needless overhead, but really
     // the other choice is to duplicate work (which the cache would prevent you
     // from doing).
     BlockCacheKey cacheKey =
         new BlockCacheKey(name, dataBlockOffset, this.isPrimaryReplicaReader(), expectedBlockType);
     boolean useLock = false;
     IdLock.Entry lockEntry = null;
     TraceScope traceScope = Trace.startSpan("HFileReaderV2.readBlock");
     try {
       while (true) {
         // Check cache for block. If found return.
         if (cacheConf.shouldReadBlockFromCache(expectedBlockType)) {
           if (useLock) {
             lockEntry = offsetLock.getLockEntry(dataBlockOffset);
           }
           // Try and get the block from the block cache. If the useLock variable is true then this
           // is the second time through the loop and it should not be counted as a block cache miss.
           HFileBlock cachedBlock = getCachedBlock(cacheKey, cacheBlock, useLock, isCompaction,
             updateCacheMetrics, expectedBlockType, expectedDataBlockEncoding);
           if (cachedBlock != null) {
             if (Trace.isTracing()) {
               traceScope.getSpan().addTimelineAnnotation("blockCacheHit");
             }
             assert cachedBlock.isUnpacked() : "Packed block leak.";
             if (cachedBlock.getBlockType().isData()) {
               if (updateCacheMetrics) {
                 HFile.DATABLOCK_READ_COUNT.increment();
               }
               // Validate encoding type for data blocks. We include encoding
               // type in the cache key, and we expect it to match on a cache hit.
               if (cachedBlock.getDataBlockEncoding() != dataBlockEncoder.getDataBlockEncoding()) {
                 throw new IOException("Cached block under key " + cacheKey + " "
                   + "has wrong encoding: " + cachedBlock.getDataBlockEncoding() + " (expected: "
                   + dataBlockEncoder.getDataBlockEncoding() + ")");
               }
             }
             // Cache-hit. Return!
             return cachedBlock;
           }
           if (!useLock && cacheBlock && cacheConf.shouldLockOnCacheMiss(expectedBlockType)) {
             // check cache again with lock
             useLock = true;
             continue;
           }
           // Carry on, please load.
         }
 
         if (Trace.isTracing()) {
           traceScope.getSpan().addTimelineAnnotation("blockCacheMiss");
         }
         // Load block from filesystem.
         HFileBlock hfileBlock = fsBlockReader.readBlockData(dataBlockOffset, onDiskBlockSize,
             pread, !isCompaction);
         validateBlockType(hfileBlock, expectedBlockType);
         HFileBlock unpacked = hfileBlock.unpack(hfileContext, fsBlockReader);
         BlockType.BlockCategory category = hfileBlock.getBlockType().getCategory();
 
         // Cache the block if necessary
         if (cacheBlock && cacheConf.shouldCacheBlockOnRead(category)) {
           cacheConf.getBlockCache().cacheBlock(cacheKey,
             cacheConf.shouldCacheCompressed(category) ? hfileBlock : unpacked,
             cacheConf.isInMemory(), this.cacheConf.isCacheDataInL1());
         }
 
         if (updateCacheMetrics && hfileBlock.getBlockType().isData()) {
           HFile.DATABLOCK_READ_COUNT.increment();
         }
 
         return unpacked;
       }
     } finally {
       traceScope.close();
       if (lockEntry != null) {
         offsetLock.releaseLockEntry(lockEntry);
       }
     }
   }
 
   @Override
   public boolean hasMVCCInfo() {
     return includesMemstoreTS && decodeMemstoreTS;
   }
 
   /**
    * Compares the actual type of a block retrieved from cache or disk with its
    * expected type and throws an exception in case of a mismatch. Expected
    * block type of {@link BlockType#DATA} is considered to match the actual
    * block type [@link {@link BlockType#ENCODED_DATA} as well.
    * @param block a block retrieved from cache or disk
    * @param expectedBlockType the expected block type, or null to skip the
    *          check
    */
   private void validateBlockType(HFileBlock block,
       BlockType expectedBlockType) throws IOException {
     if (expectedBlockType == null) {
       return;
     }
     BlockType actualBlockType = block.getBlockType();
     if (expectedBlockType.isData() && actualBlockType.isData()) {
       // We consider DATA to match ENCODED_DATA for the purpose of this
       // verification.
       return;
     }
     if (actualBlockType != expectedBlockType) {
       throw new IOException("Expected block type " + expectedBlockType + ", " +
           "but got " + actualBlockType + ": " + block);
     }
   }
 
   /**
    * @return Last key in the file. May be null if file has no entries. Note that
    *         this is not the last row key, but rather the byte form of the last
    *         KeyValue.
    */
   @Override
   public byte[] getLastKey() {
     return dataBlockIndexReader.isEmpty() ? null : lastKey;
   }
 
   /**
    * @return Midkey for this file. We work with block boundaries only so
    *         returned midkey is an approximation only.
    * @throws IOException
    */
   @Override
   public byte[] midkey() throws IOException {
     return dataBlockIndexReader.midkey();
   }
 
   @Override
   public void close() throws IOException {
     close(cacheConf.shouldEvictOnClose());
   }
 
   public void close(boolean evictOnClose) throws IOException {
     PrefetchExecutor.cancel(path);
     if (evictOnClose && cacheConf.isBlockCacheEnabled()) {
       int numEvicted = cacheConf.getBlockCache().evictBlocksByHfileName(name);
       if (LOG.isTraceEnabled()) {
         LOG.trace("On close, file=" + name + " evicted=" + numEvicted
           + " block(s)");
       }
     }
     fsBlockReader.closeStreams();
   }
 
   public DataBlockEncoding getEffectiveEncodingInCache(boolean isCompaction) {
     return dataBlockEncoder.getEffectiveEncodingInCache(isCompaction);
   }
 
   /** For testing */
   @Override
   HFileBlock.FSReader getUncachedBlockReader() {
     return fsBlockReader;
   }
 
 
   protected abstract static class AbstractScannerV2
       extends AbstractHFileReader.Scanner {
     protected HFileBlock block;
 
     @Override
     public Cell getNextIndexedKey() {
       return nextIndexedKey;
     }
     /**
      * The next indexed key is to keep track of the indexed key of the next data block.
      * If the nextIndexedKey is HConstants.NO_NEXT_INDEXED_KEY, it means that the
      * current data block is the last data block.
      *
      * If the nextIndexedKey is null, it means the nextIndexedKey has not been loaded yet.
      */
     protected Cell nextIndexedKey;
 
     public AbstractScannerV2(HFileReaderV2 r, boolean cacheBlocks,
         final boolean pread, final boolean isCompaction) {
       super(r, cacheBlocks, pread, isCompaction);
     }
 
     protected abstract ByteBuffer getFirstKeyInBlock(HFileBlock curBlock);
 
     protected abstract int loadBlockAndSeekToKey(HFileBlock seekToBlock, Cell nextIndexedKey,
         boolean rewind, Cell key, boolean seekBefore) throws IOException;
 
     @Override
     public int seekTo(byte[] key, int offset, int length) throws IOException {
       // Always rewind to the first key of the block, because the given key
       // might be before or after the current key.
       return seekTo(new KeyValue.KeyOnlyKeyValue(key, offset, length));
     }
 
     @Override
     public int reseekTo(byte[] key, int offset, int length) throws IOException {
       return reseekTo(new KeyValue.KeyOnlyKeyValue(key, offset, length));
     }
 
     @Override
     public int seekTo(Cell key) throws IOException {
       return seekTo(key, true);
     }
 
     @Override
     public int reseekTo(Cell key) throws IOException {
       int compared;
       if (isSeeked()) {
         compared = compareKey(reader.getComparator(), key);
         if (compared < 1) {
           // If the required key is less than or equal to current key, then
           // don't do anything.
           return compared;
         } else {
           // The comparison with no_next_index_key has to be checked
           if (this.nextIndexedKey != null &&
               (this.nextIndexedKey == KeyValueScanner.NO_NEXT_INDEXED_KEY || reader
               .getComparator()
                   .compareOnlyKeyPortion(key, nextIndexedKey) < 0)) {
             // The reader shall continue to scan the current data block instead
             // of querying the
             // block index as long as it knows the target key is strictly
             // smaller than
             // the next indexed key or the current data block is the last data
             // block.
             return loadBlockAndSeekToKey(this.block, nextIndexedKey, false, key, false);
           }
         }
       }
       // Don't rewind on a reseek operation, because reseek implies that we are
       // always going forward in the file.
       return seekTo(key, false);
     }
 
 
     /**
      * An internal API function. Seek to the given key, optionally rewinding to
      * the first key of the block before doing the seek.
      *
      * @param key - a cell representing the key that we need to fetch
      * @param rewind whether to rewind to the first key of the block before
      *        doing the seek. If this is false, we are assuming we never go
      *        back, otherwise the result is undefined.
      * @return -1 if the key is earlier than the first key of the file,
      *         0 if we are at the given key, 1 if we are past the given key
      *         -2 if the key is earlier than the first key of the file while
      *         using a faked index key
      * @throws IOException
      */
     public int seekTo(Cell key, boolean rewind) throws IOException {
       HFileBlockIndex.BlockIndexReader indexReader = reader.getDataBlockIndexReader();
       BlockWithScanInfo blockWithScanInfo = indexReader.loadDataBlockWithScanInfo(key, block,
           cacheBlocks, pread, isCompaction, getEffectiveDataBlockEncoding());
       if (blockWithScanInfo == null || blockWithScanInfo.getHFileBlock() == null) {
         // This happens if the key e.g. falls before the beginning of the file.
         return -1;
       }
       return loadBlockAndSeekToKey(blockWithScanInfo.getHFileBlock(),
           blockWithScanInfo.getNextIndexedKey(), rewind, key, false);
     }
 
     @Override
     public boolean seekBefore(byte[] key, int offset, int length) throws IOException {
       return seekBefore(new KeyValue.KeyOnlyKeyValue(key, offset, length));
     }
 
     @Override
     public boolean seekBefore(Cell key) throws IOException {
       HFileBlock seekToBlock = reader.getDataBlockIndexReader().seekToDataBlock(key, block,
           cacheBlocks, pread, isCompaction,
           ((HFileReaderV2) reader).getEffectiveEncodingInCache(isCompaction));
       if (seekToBlock == null) {
         return false;
       }
       ByteBuffer firstKey = getFirstKeyInBlock(seekToBlock);
 
       if (reader.getComparator()
           .compareOnlyKeyPortion(
               new KeyValue.KeyOnlyKeyValue(firstKey.array(), firstKey.arrayOffset(),
                   firstKey.limit()), key) >= 0) {
         long previousBlockOffset = seekToBlock.getPrevBlockOffset();
         // The key we are interested in
         if (previousBlockOffset == -1) {
           // we have a 'problem', the key we want is the first of the file.
           return false;
         }
 
         // It is important that we compute and pass onDiskSize to the block
         // reader so that it does not have to read the header separately to
         // figure out the size.  Currently, we do not have a way to do this
         // correctly in the general case however.
         // TODO: See https://issues.apache.org/jira/browse/HBASE-14576
         int prevBlockSize = -1;
         seekToBlock = reader.readBlock(previousBlockOffset,
             prevBlockSize, cacheBlocks,
             pread, isCompaction, true, BlockType.DATA, getEffectiveDataBlockEncoding());
         // TODO shortcut: seek forward in this block to the last key of the
         // block.
       }
       Cell firstKeyInCurrentBlock = new KeyValue.KeyOnlyKeyValue(Bytes.getBytes(firstKey));
       loadBlockAndSeekToKey(seekToBlock, firstKeyInCurrentBlock, true, key, true);
       return true;
     }
 
     /**
      * Scans blocks in the "scanned" section of the {@link HFile} until the next
      * data block is found.
      *
      * @return the next block, or null if there are no more data blocks
      * @throws IOException
      */
     @edu.umd.cs.findbugs.annotations.SuppressWarnings(value="NP_NULL_ON_SOME_PATH",
         justification="Yeah, unnecessary null check; could do w/ clean up")
     protected HFileBlock readNextDataBlock() throws IOException {
       long lastDataBlockOffset = reader.getTrailer().getLastDataBlockOffset();
       if (block == null)
         return null;
 
       HFileBlock curBlock = block;
 
       do {
         if (curBlock.getOffset() >= lastDataBlockOffset) {
           return null;
         }
 
         if (curBlock.getOffset() < 0) {
           throw new IOException("Invalid block file offset: " + block);
         }
 
         // We are reading the next block without block type validation, because
         // it might turn out to be a non-data block.
         curBlock = reader.readBlock(curBlock.getOffset()
             + curBlock.getOnDiskSizeWithHeader(),
             curBlock.getNextBlockOnDiskSize(), cacheBlocks, pread,
             isCompaction, true, null, getEffectiveDataBlockEncoding());
       } while (!curBlock.getBlockType().isData());
 
       return curBlock;
     }
 
     public DataBlockEncoding getEffectiveDataBlockEncoding() {
       return ((HFileReaderV2)reader).getEffectiveEncodingInCache(isCompaction);
     }
     /**
      * Compare the given key against the current key
      * @param comparator
      * @param key
      * @param offset
      * @param length
      * @return -1 is the passed key is smaller than the current key, 0 if equal and 1 if greater
      */
     public abstract int compareKey(KVComparator comparator, byte[] key, int offset,
         int length);
 
     public abstract int compareKey(KVComparator comparator, Cell kv);
   }
 
   /**
    * Implementation of {@link HFileScanner} interface.
    */
   protected static class ScannerV2 extends AbstractScannerV2 {
     private HFileReaderV2 reader;
 
     public ScannerV2(HFileReaderV2 r, boolean cacheBlocks,
         final boolean pread, final boolean isCompaction) {
       super(r, cacheBlocks, pread, isCompaction);
       this.reader = r;
     }
 
     @Override
     public Cell getKeyValue() {
       if (!isSeeked())
         return null;
 
       return formNoTagsKeyValue();
     }
 
     protected Cell formNoTagsKeyValue() {
       NoTagsKeyValue ret = new NoTagsKeyValue(blockBuffer.array(), blockBuffer.arrayOffset()
           + blockBuffer.position(), getCellBufSize());
       if (this.reader.shouldIncludeMemstoreTS()) {
         ret.setSequenceId(currMemstoreTS);
       }
       return ret;
     }
 
     protected int getCellBufSize() {
       return KEY_VALUE_LEN_SIZE + currKeyLen + currValueLen;
     }
 
     @Override
     public ByteBuffer getKey() {
       assertSeeked();
       return ByteBuffer.wrap(
           blockBuffer.array(),
           blockBuffer.arrayOffset() + blockBuffer.position()
               + KEY_VALUE_LEN_SIZE, currKeyLen).slice();
     }
 
     @Override
     public int compareKey(KVComparator comparator, byte[] key, int offset, int length) {
       return comparator.compareFlatKey(key, offset, length, blockBuffer.array(),
           blockBuffer.arrayOffset() + blockBuffer.position() + KEY_VALUE_LEN_SIZE, currKeyLen);
     }
 
     @Override
     public ByteBuffer getValue() {
       assertSeeked();
       return ByteBuffer.wrap(
           blockBuffer.array(),
           blockBuffer.arrayOffset() + blockBuffer.position()
               + KEY_VALUE_LEN_SIZE + currKeyLen, currValueLen).slice();
     }
 
     protected void setNonSeekedState() {
       block = null;
       blockBuffer = null;
       currKeyLen = 0;
       currValueLen = 0;
       currMemstoreTS = 0;
       currMemstoreTSLen = 0;
     }
 
     /**
      * Set the position on current backing blockBuffer.
      */
     private void positionThisBlockBuffer() {
       try {
         blockBuffer.position(getNextCellStartPosition());
       } catch (IllegalArgumentException e) {
         LOG.error("Current pos = " + blockBuffer.position()
             + "; currKeyLen = " + currKeyLen + "; currValLen = "
             + currValueLen + "; block limit = " + blockBuffer.limit()
             + "; HFile name = " + reader.getName()
             + "; currBlock currBlockOffset = " + block.getOffset());
         throw e;
       }
     }
 
     /**
      * Set our selves up for the next 'next' invocation, set up next block.
      * @return True is more to read else false if at the end.
      * @throws IOException
      */
     private boolean positionForNextBlock() throws IOException {
       // Methods are small so they get inlined because they are 'hot'.
       long lastDataBlockOffset = reader.getTrailer().getLastDataBlockOffset();
       if (block.getOffset() >= lastDataBlockOffset) {
         setNonSeekedState();
         return false;
       }
       return isNextBlock();
     }
 
     private boolean isNextBlock() throws IOException {
       // Methods are small so they get inlined because they are 'hot'.
       HFileBlock nextBlock = readNextDataBlock();
       if (nextBlock == null) {
         setNonSeekedState();
         return false;
       }
       updateCurrBlock(nextBlock);
       return true;
     }
 
     private final boolean _next() throws IOException {
       // Small method so can be inlined. It is a hot one.
       if (blockBuffer.remaining() <= 0) {
         return positionForNextBlock();
       }
       // We are still in the same block.
       readKeyValueLen();
       return true;
     }
 
     /**
      * Go to the next key/value in the block section. Loads the next block if
      * necessary. If successful, {@link #getKey()} and {@link #getValue()} can
      * be called.
      *
      * @return true if successfully navigated to the next key/value
      */
     @Override
     public boolean next() throws IOException {
       // This is a hot method so extreme measures taken to ensure it is small and inlineable.
       // Checked by setting: -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining -XX:+PrintCompilation
       assertSeeked();
       positionThisBlockBuffer();
       return _next();
     }
 
     protected int getNextCellStartPosition() {
       return blockBuffer.position() + KEY_VALUE_LEN_SIZE + currKeyLen + currValueLen
           + currMemstoreTSLen;
     }
 
     /**
      * Positions this scanner at the start of the file.
      *
      * @return false if empty file; i.e. a call to next would return false and
      *         the current key and value are undefined.
      * @throws IOException
      */
     @Override
     public boolean seekTo() throws IOException {
       if (reader == null) {
         return false;
       }
 
       if (reader.getTrailer().getEntryCount() == 0) {
         // No data blocks.
         return false;
       }
 
       long firstDataBlockOffset =
           reader.getTrailer().getFirstDataBlockOffset();
       if (block != null && block.getOffset() == firstDataBlockOffset) {
         blockBuffer.rewind();
         readKeyValueLen();
         return true;
       }
 
       block = reader.readBlock(firstDataBlockOffset, -1, cacheBlocks, pread,
           isCompaction, true, BlockType.DATA, getEffectiveDataBlockEncoding());
       if (block.getOffset() < 0) {
         throw new IOException("Invalid block offset: " + block.getOffset());
       }
       updateCurrBlock(block);
       return true;
     }
 
     @Override
     protected int loadBlockAndSeekToKey(HFileBlock seekToBlock, Cell nextIndexedKey,
         boolean rewind, Cell key, boolean seekBefore) throws IOException {
       if (block == null || block.getOffset() != seekToBlock.getOffset()) {
         updateCurrBlock(seekToBlock);
       } else if (rewind) {
         blockBuffer.rewind();
       }
 
       // Update the nextIndexedKey
       this.nextIndexedKey = nextIndexedKey;
       return blockSeek(key, seekBefore);
     }
 
     /**
      * Updates the current block to be the given {@link HFileBlock}. Seeks to
      * the the first key/value pair.
      *
      * @param newBlock the block to make current
      */
     protected void updateCurrBlock(HFileBlock newBlock) {
       block = newBlock;
 
       // sanity check
       if (block.getBlockType() != BlockType.DATA) {
         throw new IllegalStateException("ScannerV2 works only on data " +
             "blocks, got " + block.getBlockType() + "; " +
             "fileName=" + reader.name + ", " +
             "dataBlockEncoder=" + reader.dataBlockEncoder + ", " +
             "isCompaction=" + isCompaction);
       }
 
       blockBuffer = block.getBufferWithoutHeader();
       readKeyValueLen();
       blockFetches.incrementAndGet();
 
       // Reset the next indexed key
       this.nextIndexedKey = null;
     }
 
     /**
      * @param v
      * @return True if v &lt;= 0 or v &gt; current block buffer limit.
      */
     protected final boolean checkKeyLen(final int v) {
       return v <= 0 || v > this.blockBuffer.limit();
     }
 
     /**
      * @param v
      * @return True if v &lt; 0 or v &gt; current block buffer limit.
      */
     protected final boolean checkLen(final int v) {
       return v < 0 || v > this.blockBuffer.limit();
     }
 
     /**
      * Check key and value lengths are wholesome.
      */
     protected final void checkKeyValueLen() {
       if (checkKeyLen(this.currKeyLen) || checkLen(this.currValueLen)) {
         throw new IllegalStateException("Invalid currKeyLen " + this.currKeyLen +
           " or currValueLen " + this.currValueLen + ". Block offset: " + block.getOffset() +
           ", block length: " + this.blockBuffer.limit() + ", position: " +
            this.blockBuffer.position() + " (without header).");
       }
     }
 
     protected void readKeyValueLen() {
       // TODO: METHOD (mostly) DUPLICATED IN V3!!!!! FIXED in master branch by collapsing v3 and v2.
       // This is a hot method. We go out of our way to make this method short so it can be
       // inlined and is not too big to compile. We also manage position in ByteBuffer ourselves
       // because it is faster than going via range-checked ByteBuffer methods or going through a
       // byte buffer array a byte at a time.
       int p = blockBuffer.position() + blockBuffer.arrayOffset();
       // Get a long at a time rather than read two individual ints. In micro-benchmarking, even
       // with the extra bit-fiddling, this is order-of-magnitude faster than getting two ints.
       long ll = Bytes.toLong(blockBuffer.array(), p);
       // Read top half as an int of key length and bottom int as value length
       this.currKeyLen = (int)(ll >> Integer.SIZE);
       this.currValueLen = (int)(Bytes.MASK_FOR_LOWER_INT_IN_LONG ^ ll);
       checkKeyValueLen();
       // Move position past the key and value lengths and then beyond the key and value
       p += (Bytes.SIZEOF_LONG + currKeyLen + currValueLen);
       readMvccVersion(p);
     }
 
     /**
      * Read mvcc. Does checks to see if we even need to read the mvcc at all.
      * @param position
      */
     protected void readMvccVersion(final int position) {
       // See if we even need to decode mvcc.
       if (!this.reader.shouldIncludeMemstoreTS()) return;
       if (!this.reader.decodeMemstoreTS) {
         currMemstoreTS = 0;
         currMemstoreTSLen = 1;
         return;
       }
       _readMvccVersion(position);
     }
 
     /**
      * Actually do the mvcc read. Does no checks.
      * @param position
      */
     private void _readMvccVersion(final int position) {
       // This is Bytes#bytesToVint inlined so can save a few instructions in this hot method; i.e.
       // previous if one-byte vint, we'd redo the vint call to find int size.
       // Also the method is kept small so can be inlined.
       byte firstByte = blockBuffer.array()[position];
       int len = WritableUtils.decodeVIntSize(firstByte);
       if (len == 1) {
         this.currMemstoreTS = firstByte;
       } else {
         long i = 0;
         for (int idx = 0; idx < len - 1; idx++) {
           byte b = blockBuffer.array()[position + 1 + idx];
           i = i << 8;
           i = i | (b & 0xFF);
         }
         currMemstoreTS = (WritableUtils.isNegativeVInt(firstByte) ? ~i : i);
       }
       this.currMemstoreTSLen = len;
     }
 
     protected void readMvccVersion() {
       // TODO CLEANUP!!!
       readMvccVersion(blockBuffer.arrayOffset() + blockBuffer.position());
     }
 
     /**
      * Within a loaded block, seek looking for the last key that is smaller than
      * (or equal to?) the key we are interested in.
      *
      * A note on the seekBefore: if you have seekBefore = true, AND the first
      * key in the block = key, then you'll get thrown exceptions. The caller has
      * to check for that case and load the previous block as appropriate.
      *
      * @param key
      *          the key to find
      * @param seekBefore
      *          find the key before the given key in case of exact match.
      * @return 0 in case of an exact key match, 1 in case of an inexact match,
      *         -2 in case of an inexact match and furthermore, the input key
      *         less than the first key of current block(e.g. using a faked index
      *         key)
      */
     protected int blockSeek(Cell key, boolean seekBefore) {
       int klen, vlen;
       long memstoreTS = 0;
       int memstoreTSLen = 0;
       int lastKeyValueSize = -1;
       KeyValue.KeyOnlyKeyValue keyOnlykv = new KeyValue.KeyOnlyKeyValue();
       do {
         blockBuffer.mark();
         klen = blockBuffer.getInt();
         vlen = blockBuffer.getInt();
         if (checkKeyLen(klen) || checkLen(vlen)) {
           throw new IllegalStateException("Invalid klen " + klen + " or vlen "
               + vlen + ". Block offset: "
               + block.getOffset() + ", block length: " + blockBuffer.limit() + ", position: "
               + blockBuffer.position() + " (without header).");
         }
         blockBuffer.reset();
         if (this.reader.shouldIncludeMemstoreTS()) {
           if (this.reader.decodeMemstoreTS) {
             int memstoreTSOffset = blockBuffer.arrayOffset() + blockBuffer.position()
                 + KEY_VALUE_LEN_SIZE + klen + vlen;
             memstoreTS = Bytes.readAsVLong(blockBuffer.array(), memstoreTSOffset);
             memstoreTSLen = WritableUtils.getVIntSize(memstoreTS);
           } else {
             memstoreTS = 0;
             memstoreTSLen = 1;
           }
         }
 
         int keyOffset = blockBuffer.arrayOffset() + blockBuffer.position() + KEY_VALUE_LEN_SIZE;
         keyOnlykv.setKey(blockBuffer.array(), keyOffset, klen);
         int comp = reader.getComparator().compareOnlyKeyPortion(key, keyOnlykv);
 
         if (comp == 0) {
           if (seekBefore) {
             if (lastKeyValueSize < 0) {
               throw new IllegalStateException("blockSeek with seekBefore "
                   + "at the first key of the block: key="
                   + CellUtil.getCellKeyAsString(key)
                   + ", blockOffset=" + block.getOffset() + ", onDiskSize="
                   + block.getOnDiskSizeWithHeader());
             }
             blockBuffer.position(blockBuffer.position() - lastKeyValueSize);
             readKeyValueLen();
             return 1; // non exact match.
           }
           currKeyLen = klen;
           currValueLen = vlen;
           if (this.reader.shouldIncludeMemstoreTS()) {
             currMemstoreTS = memstoreTS;
             currMemstoreTSLen = memstoreTSLen;
           }
           return 0; // indicate exact match
         } else if (comp < 0) {
           if (lastKeyValueSize > 0)
             blockBuffer.position(blockBuffer.position() - lastKeyValueSize);
           readKeyValueLen();
           if (lastKeyValueSize == -1 && blockBuffer.position() == 0
               && this.reader.trailer.getMinorVersion() >= MINOR_VERSION_WITH_FAKED_KEY) {
             return HConstants.INDEX_KEY_MAGIC;
           }
           return 1;
         }
 
         // The size of this key/value tuple, including key/value length fields.
         lastKeyValueSize = klen + vlen + memstoreTSLen + KEY_VALUE_LEN_SIZE;
         blockBuffer.position(blockBuffer.position() + lastKeyValueSize);
       } while (blockBuffer.remaining() > 0);
 
       // Seek to the last key we successfully read. This will happen if this is
       // the last key/value pair in the file, in which case the following call
       // to next() has to return false.
       blockBuffer.position(blockBuffer.position() - lastKeyValueSize);
       readKeyValueLen();
       return 1; // didn't exactly find it.
     }
 
     @Override
     protected ByteBuffer getFirstKeyInBlock(HFileBlock curBlock) {
       ByteBuffer buffer = curBlock.getBufferWithoutHeader();
       // It is safe to manipulate this buffer because we own the buffer object.
       buffer.rewind();
       int klen = buffer.getInt();
       buffer.getInt();
       ByteBuffer keyBuff = buffer.slice();
       keyBuff.limit(klen);
       keyBuff.rewind();
       return keyBuff;
     }
 
     @Override
     public String getKeyString() {
       return Bytes.toStringBinary(blockBuffer.array(),
           blockBuffer.arrayOffset() + blockBuffer.position()
               + KEY_VALUE_LEN_SIZE, currKeyLen);
     }
 
     @Override
     public String getValueString() {
       return Bytes.toString(blockBuffer.array(), blockBuffer.arrayOffset()
           + blockBuffer.position() + KEY_VALUE_LEN_SIZE + currKeyLen,
           currValueLen);
     }
 
     @Override
     public int compareKey(KVComparator comparator, Cell key) {
       return comparator.compareOnlyKeyPortion(
           key,
           new KeyValue.KeyOnlyKeyValue(blockBuffer.array(), blockBuffer.arrayOffset()
               + blockBuffer.position() + KEY_VALUE_LEN_SIZE, currKeyLen));
     }
   }
 
   /**
    * ScannerV2 that operates on encoded data blocks.
    */
   protected static class EncodedScannerV2 extends AbstractScannerV2 {
     private final HFileBlockDecodingContext decodingCtx;
     private final DataBlockEncoder.EncodedSeeker seeker;
     private final DataBlockEncoder dataBlockEncoder;
     protected final HFileContext meta;
 
     public EncodedScannerV2(HFileReaderV2 reader, boolean cacheBlocks,
         boolean pread, boolean isCompaction, HFileContext meta) {
       super(reader, cacheBlocks, pread, isCompaction);
       DataBlockEncoding encoding = reader.dataBlockEncoder.getDataBlockEncoding();
       dataBlockEncoder = encoding.getEncoder();
       decodingCtx = dataBlockEncoder.newDataBlockDecodingContext(meta);
       seeker = dataBlockEncoder.createSeeker(
         reader.getComparator(), decodingCtx);
       this.meta = meta;
     }
 
     @Override
     public boolean isSeeked(){
       return this.block != null;
     }
 
     /**
      * Updates the current block to be the given {@link HFileBlock}. Seeks to
      * the the first key/value pair.
      *
      * @param newBlock the block to make current
      * @throws CorruptHFileException
      */
     private void updateCurrentBlock(HFileBlock newBlock) throws CorruptHFileException {
       block = newBlock;
 
       // sanity checks
       if (block.getBlockType() != BlockType.ENCODED_DATA) {
         throw new IllegalStateException(
             "EncodedScanner works only on encoded data blocks");
       }
       short dataBlockEncoderId = block.getDataBlockEncodingId();
       if (!DataBlockEncoding.isCorrectEncoder(dataBlockEncoder, dataBlockEncoderId)) {
         String encoderCls = dataBlockEncoder.getClass().getName();
         throw new CorruptHFileException("Encoder " + encoderCls
           + " doesn't support data block encoding "
           + DataBlockEncoding.getNameFromId(dataBlockEncoderId));
       }
 
       seeker.setCurrentBuffer(getEncodedBuffer(newBlock));
       blockFetches.incrementAndGet();
 
       // Reset the next indexed key
       this.nextIndexedKey = null;
     }
 
     private ByteBuffer getEncodedBuffer(HFileBlock newBlock) {
       ByteBuffer origBlock = newBlock.getBufferReadOnly();
       ByteBuffer encodedBlock = ByteBuffer.wrap(origBlock.array(),
           origBlock.arrayOffset() + newBlock.headerSize() +
           DataBlockEncoding.ID_SIZE,
           newBlock.getUncompressedSizeWithoutHeader() -
           DataBlockEncoding.ID_SIZE).slice();
       return encodedBlock;
     }
 
     @Override
     public boolean seekTo() throws IOException {
       if (reader == null) {
         return false;
       }
 
       if (reader.getTrailer().getEntryCount() == 0) {
         // No data blocks.
         return false;
       }
 
       long firstDataBlockOffset =
           reader.getTrailer().getFirstDataBlockOffset();
       if (block != null && block.getOffset() == firstDataBlockOffset) {
         seeker.rewind();
         return true;
       }
 
       block = reader.readBlock(firstDataBlockOffset, -1, cacheBlocks, pread,
           isCompaction, true, BlockType.DATA, getEffectiveDataBlockEncoding());
       if (block.getOffset() < 0) {
         throw new IOException("Invalid block offset: " + block.getOffset());
       }
       updateCurrentBlock(block);
       return true;
     }
 
     @Override
     public boolean next() throws IOException {
       boolean isValid = seeker.next();
       if (!isValid) {
         block = readNextDataBlock();
         isValid = block != null;
         if (isValid) {
           updateCurrentBlock(block);
         }
       }
       return isValid;
     }
 
     @Override
     public ByteBuffer getKey() {
       assertValidSeek();
       return seeker.getKeyDeepCopy();
     }
 
     @Override
     public int compareKey(KVComparator comparator, byte[] key, int offset, int length) {
       return seeker.compareKey(comparator, key, offset, length);
     }
 
     @Override
     public ByteBuffer getValue() {
       assertValidSeek();
       return seeker.getValueShallowCopy();
     }
 
     @Override
     public Cell getKeyValue() {
       if (block == null) {
         return null;
       }
       return seeker.getKeyValue();
     }
 
     @Override
     public String getKeyString() {
       ByteBuffer keyBuffer = getKey();
       return Bytes.toStringBinary(keyBuffer.array(),
           keyBuffer.arrayOffset(), keyBuffer.limit());
     }
 
     @Override
     public String getValueString() {
       ByteBuffer valueBuffer = getValue();
       return Bytes.toStringBinary(valueBuffer.array(),
           valueBuffer.arrayOffset(), valueBuffer.limit());
     }
 
     private void assertValidSeek() {
       if (block == null) {
         throw new NotSeekedException();
       }
     }
 
     @Override
     protected ByteBuffer getFirstKeyInBlock(HFileBlock curBlock) {
       return dataBlockEncoder.getFirstKeyInBlock(getEncodedBuffer(curBlock));
     }
 
     @Override
     protected int loadBlockAndSeekToKey(HFileBlock seekToBlock, Cell nextIndexedKey,
         boolean rewind, Cell key, boolean seekBefore) throws IOException {
       if (block == null || block.getOffset() != seekToBlock.getOffset()) {
         updateCurrentBlock(seekToBlock);
       } else if (rewind) {
         seeker.rewind();
       }
       this.nextIndexedKey = nextIndexedKey;
       return seeker.seekToKeyInBlock(key, seekBefore);
     }
 
     @Override
     public int compareKey(KVComparator comparator, Cell key) {
       return seeker.compareKey(comparator, key);
     }
   }
 
   /**
    * Returns a buffer with the Bloom filter metadata. The caller takes
    * ownership of the buffer.
    */
   @Override
   public DataInput getGeneralBloomFilterMetadata() throws IOException {
     return this.getBloomFilterMetadata(BlockType.GENERAL_BLOOM_META);
   }
 
   @Override
   public DataInput getDeleteBloomFilterMetadata() throws IOException {
     return this.getBloomFilterMetadata(BlockType.DELETE_FAMILY_BLOOM_META);
   }
 
   private DataInput getBloomFilterMetadata(BlockType blockType)
   throws IOException {
     if (blockType != BlockType.GENERAL_BLOOM_META &&
         blockType != BlockType.DELETE_FAMILY_BLOOM_META) {
       throw new RuntimeException("Block Type: " + blockType.toString() +
           " is not supported") ;
     }
 
     for (HFileBlock b : loadOnOpenBlocks)
       if (b.getBlockType() == blockType)
         return b.getByteStream();
     return null;
   }
 
   @Override
   public boolean isFileInfoLoaded() {
     return true; // We load file info in constructor in version 2.
   }
 
   /**
    * Validates that the minor version is within acceptable limits.
    * Otherwise throws an Runtime exception
    */
   private void validateMinorVersion(Path path, int minorVersion) {
     if (minorVersion < MIN_MINOR_VERSION ||
         minorVersion > MAX_MINOR_VERSION) {
       String msg = "Minor version for path " + path +
                    " is expected to be between " +
                    MIN_MINOR_VERSION + " and " + MAX_MINOR_VERSION +
                    " but is found to be " + minorVersion;
       LOG.error(msg);
       throw new RuntimeException(msg);
     }
   }
 
   @Override
   public int getMajorVersion() {
     return 2;
   }
 
   @Override
   public HFileContext getFileContext() {
     return hfileContext;
   }
 
   /**
    * Returns false if block prefetching was requested for this file and has
    * not completed, true otherwise
    */
   boolean prefetchComplete() {
     return PrefetchExecutor.isCompleted(path);
   }
 
   @Override
   public void unbufferStream() {
     fsBlockReader.unbufferStream();
   }
 }