public void rollWalFileIfHaveNoActiveMemTable() {
      long firstVersionId = checkpointManager.getFirstValidWALVersionId();
      if (firstVersionId == Long.MIN_VALUE) {
        // roll wal log writer to delete current wal file
        if (buffer.getCurrentWALOriginalFileSize() > 0) {
          rollWALFile();
        }
      }
    }
This means that the relevant memTable in the file has been successfully flushed, so we should
scroll through a new wal file so that the current file can be deleted
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/node/WALNode.java