@Override
  public void clear() {
    super.clear();
    cachedEngineStatistics.updatePinnedMNodeNum(-pinnedMNodeNum.get());
    cachedEngineStatistics.updateUnpinnedMNodeNum(-unpinnedMNodeNum.get());
    cachedEngineStatistics.updatePinnedMemorySize(-pinnedMemorySize.get());
    cachedEngineStatistics.updateUnpinnedMemorySize(-unpinnedMemorySize.get());
  }
This class is used to record statistics within a SchemaRegion in PBTree mode, which is a superset
of the statistics in Memory mode.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/rescon/CachedSchemaRegionStatistics.java