public void deleteWALNode(String applicantUniqueId) {
    nodesLock.lock();
    try {
      WALNode walNode = identifier2Nodes.remove(applicantUniqueId);
      if (walNode != null) {
        walNode.setDeleted(true);
        walNode.close();
        if (walNode.getLogDirectory().exists()) {
          FileUtils.deleteFileOrDirectory(walNode.getLogDirectory());
        }
        WALManager.getInstance().subtractTotalDiskUsage(walNode.getDiskUsage());
        WALManager.getInstance().subtractTotalFileNum(walNode.getFileNum());
      }
    } finally {
      nodesLock.unlock();
    }
  }
This strategy creates one wal node for each unique identifier. In other words, each identifier
(like data region) has its own wal node.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/allocation/FirstCreateStrategy.java