@Override
  public void setAlias(final IMeasurementMNode<IMemMNode> measurementMNode, final String alias) {
    final String existingAlias = measurementMNode.getAlias();
    if (existingAlias == null && alias == null) {
      return;
    }

    measurementMNode.setAlias(alias);

    if (existingAlias != null && alias != null) {
      int delta = alias.length() - existingAlias.length();
      if (delta > 0) {
        requestMemory(delta);
      } else if (delta < 0) {
        releaseMemory(-delta);
      }
    } else if (alias == null) {
      releaseMemory(MNodeSizeEstimator.getAliasBaseSize() + existingAlias.length());
    } else {
      requestMemory(MNodeSizeEstimator.getAliasBaseSize() + alias.length());
    }
  }
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