protected ICachedMNode onReturnLeft(ICachedMNode ansMNode) {
        ICachedMNode nodeInMem = parent.getChild(ansMNode.getName());
        if (nodeInMem != null) {
          try {
            memoryManager.updateCacheStatusAfterMemoryRead(nodeInMem);
            ansMNode = nodeInMem;
          } catch (MNodeNotCachedException e) {
            ansMNode = loadChildFromDiskToParent(parent, ansMNode);
          }
        } else {
          ansMNode = loadChildFromDiskToParent(parent, ansMNode);
        }
        return ansMNode;
      }
Since any node R/W operation may change the memory status, thus it should be controlled during
iterating child nodes.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/pbtree/CachedMTreeStore.java