private void init() {
    checkpoints = new ArrayList<>();
    try (DataInputStream logStream = new DataInputStream(new WALInputStream(logFile))) {
      maxMemTableId = logStream.readLong();
      while (logStream.available() > 0) {
        Checkpoint checkpoint = Checkpoint.deserialize(logStream);
        checkpoints.add(checkpoint);
      }
    } catch (IOException e) {
      logger.warn(
          "Meet error when reading checkpoint file {}, skip broken checkpoints", logFile, e);
    }
  }
CheckpointReader is used to read all checkpoints from .checkpoint file.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/io/CheckpointReader.java