@Override
  public void clear() {
    nodesLock.lock();
    try {
      nodeCursor = -1;
      nodeIdCounter = -1;
      for (WALNode walNode : walNodes) {
        walNode.close();
      }
      walNodes.clear();
    } finally {
      nodesLock.unlock();
    }
  }
This strategy creates n wal nodes and allocate them by round-robin strategy. In other words,
several identifiers (like data regions) can share one wal node.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/allocation/RoundRobinStrategy.java