public static MemMTreeStore loadFromSnapshot(
      final File snapshotDir,
      final Consumer<IMeasurementMNode<IMemMNode>> measurementProcess,
      final Consumer<IDeviceMNode<IMemMNode>> deviceProcess,
      final BiConsumer<IDeviceMNode<IMemMNode>, String> tableDeviceProcess,
      final MemSchemaRegionStatistics regionStatistics,
      final SchemaRegionMemMetric metric)
      throws IOException {
    return new MemMTreeStore(
        MemMTreeSnapshotUtil.loadSnapshot(
            snapshotDir, measurementProcess, deviceProcess, tableDeviceProcess, regionStatistics),
        regionStatistics,
        metric);
  }
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