@Override
  public long getFlushedTime(long timePartitionId, IDeviceID deviceId) {
    return partitionLatestFlushedTime.get(timePartitionId).getLastFlushTime(deviceId);
  }
record memory cost of map for each partitionId
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/HashLastFlushTimeMap.java