@Override
  public int serializedSize() {
    int size = FIXED_SERIALIZED_SIZE;
    for (MemTableInfo memTableInfo : memTableInfos) {
      size += memTableInfo.serializedSize();
    }
    return size;
  }
Checkpoint is the basic element of .checkpoint file, including type, number of memTables, and
brief information of each memTable.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/checkpoint/Checkpoint.java