@Override
  public Iterator<ICachedMNode> updateCacheStatusAndRetrieveSubtreeAfterPersist(
      ICachedMNode subtreeRoot) {
    return new VolatileSubtreeIterator(getCachedMNodeContainer(subtreeRoot));
  }
Collect updated storage group node.

@return null if not exist
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/memory/MemoryManager.java