@Override
  public IMNodeIterator<IMemMNode> getChildrenIterator(final IMemMNode parent) {
    return new MNodeIterator<>(parent.getChildren().values().iterator());
  }
This is a memory-based implementation of IMTreeStore. All MNodes are stored in memory.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/impl/mem/MemMTreeStore.java