public Map<String[], Long> getAllTTLs() {
    Map<String[], Long> result = new HashMap<>();
    List<String> pathNodes = new ArrayList<>();
    pathNodes.add(IoTDBConstant.PATH_ROOT);
    dfsCacheTree(result, pathNodes, ttlCacheTree);
    return result;
  }
@return key is path contains wildcard between each node
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/ttl/TTLCache.java