public void open() throws IOException {
    if (stream == null) {
      stream = fs.open(logFile);
    }

    if (header == null) {
      header = ProcedureWALFormat.readHeader(stream);
      startPos = stream.getPos();
    } else {
      stream.seek(startPos);
    }
  }
Describes a WAL File
@deprecated Since 2.3.0, will be removed in 4.0.0. Keep here only for rolling upgrading, now we
            use the new region based procedure store.
hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/store/wal/ProcedureWALFile.java