private void dfsCacheTree(
      Map<String[], Long> pathTTLMap, List<String> pathNodes, CacheNode node) {
    if (node.ttl != NULL_TTL) {
      pathTTLMap.put(pathNodes.toArray(new String[0]), node.ttl);
    }
    for (Map.Entry<String, CacheNode> entry : node.getChildren().entrySet()) {
      pathNodes.add(entry.getKey());
      dfsCacheTree(pathTTLMap, pathNodes, entry.getValue());
      pathNodes.remove(pathNodes.size() - 1);
    }
  }
@return key is path contains wildcard between each node
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/ttl/TTLCache.java