@Override
    protected void setup(Context context) throws IOException, InterruptedException {
      targetBatchSize =
        context.getConfiguration().getLong(HASH_BATCH_SIZE_CONF_KEY, DEFAULT_BATCH_SIZE);
      hasher = new ResultHasher();
      hasher.ignoreTimestamps = context.getConfiguration().getBoolean(IGNORE_TIMESTAMPS, false);
      TableSplit split = (TableSplit) context.getInputSplit();
      hasher.startBatch(new ImmutableBytesWritable(split.getStartRow()));
    }
Get the current hash
@return the current hash or null if there is no current hash
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/HashTable.java