private void openReader(Path path) throws IOException {
      closeReader();
      reader = openReader(path, currentPos > 0 ? currentPos : -1);
      setCurrentPath(path);
    }
{@link RecordReader} for an {@link WAL} file. Implementation shared with deprecated
HLogInputFormat.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/WALInputFormat.java