@Override
  public synchronized void addReference(
      TsFileResource tsFileResource, ModificationFile modificationFile) {
    modFileReferences.computeIfAbsent(modificationFile, f -> new HashSet<>()).add(tsFileResource);
  }
LevelModFileManager manages the shared mod files within one time partition.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/modification/PartitionLevelModFileManager.java