@Override
  public void degradeLastFlushTime(long partitionId) {
    partitionLatestFlushedTime.computeIfPresent(
        partitionId, (id, lastFlushTime) -> lastFlushTime.degradeLastFlushTime());
    memCostForEachPartition.put(partitionId, (long) Long.BYTES);
  }
record memory cost of map for each partitionId
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/HashLastFlushTimeMap.java