@Override
  public RecordReader<WALKey, WALEdit> createRecordReader(InputSplit split,
    TaskAttemptContext context) throws IOException, InterruptedException {
    return new WALKeyRecordReader();
  }
@param startTime If file looks like it has a timestamp in its name, we'll check if newer or
                 equal to this value else we will filter out the file. If name does not seem to
                 have a timestamp, we will just return it w/o filtering.
@param endTime   If file looks like it has a timestamp in its name, we'll check if older or
                 equal to this value else we will filter out the file. If name does not seem to
                 have a timestamp, we will just return it w/o filtering.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/WALInputFormat.java