@Override
  public ReqIterator getReqIterator(long startIndex) {
    return new PlanNodeIterator(startIndex);
  }
This iterator is not concurrency-safe, cannot read the current-writing wal file.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/node/WALNode.java