public int compareKey(CellComparator comparator, ExtendedCell key) {
      blockBuffer.asSubByteBuffer(blockBuffer.position() + KEY_VALUE_LEN_SIZE, currKeyLen, pair);
      this.bufBackedKeyOnlyKv.setKey(pair.getFirst(), pair.getSecond(), currKeyLen, rowLen);
      return PrivateCellUtil.compareKeyIgnoresMvcc(comparator, key, this.bufBackedKeyOnlyKv);
    }
Updates the current block to be the given {@link HFileBlock}. Seeks to the the first
key/value pair.
@param newBlock the block read by {@link HFileReaderImpl#readBlock}, it's a totally new block
                with new allocated {@link ByteBuff}, so if no further reference to this
                block, we should release it carefully.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderImpl.java