private List<Long> initPinnedMemTableIds() {
      List<MemTableInfo> memTableInfos = checkpointManager.activeOrPinnedMemTables();
      if (memTableInfos.isEmpty()) {
        return new ArrayList<>();
      }
      List<Long> pinnedIds = new ArrayList<>();
      for (MemTableInfo memTableInfo : memTableInfos) {
        if (memTableInfo.isFlushed() && memTableInfo.isPinned()) {
          pinnedIds.add(memTableInfo.getMemTableId());
        }
      }
      return pinnedIds;
    }
This means that the relevant memTable in the file has been successfully flushed, so we should
scroll through a new wal file so that the current file can be deleted
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/node/WALNode.java