聊聊claudb的transaction command

序

本文主要研究一下claudb的transaction command

TransactionState

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/TransactionState.java

public class TransactionState implements Iterable<Request> {

  private List<Request> requests = new LinkedList<>();

  public void enqueue(Request request) {
    requests.add(request);
  }

  public int size() {
    return requests.size();
  }

  @Override
  public Iterator<Request> iterator() {
    return requests.iterator();
  }
}

• TransactionState实现了Iterable<Request>接口，它定义了requests属性，提供了enqueue方法将request添加到requests中

MultiCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/MultiCommand.java

@Command("multi")
@TxIgnore
public class MultiCommand implements DBCommand {

  private static final String TRASACTION_KEY = "tx";

  @Override
  public RedisToken execute(Database db, Request request) {
    if (!isTxActive(request.getSession())) {
      createTransaction(request.getSession());
      return responseOk();
    } else {
      return error("ERR MULTI calls can not be nested");
    }
  }

  private void createTransaction(Session session) {
    session.putValue(TRASACTION_KEY, new TransactionState());
  }

  private boolean isTxActive(Session session) {
    return session.getValue(TRASACTION_KEY).isPresent();
  }
}

• MultiCommand实现了DBCommand接口，其execute方法先判断isTxActive，非active的话才createTransaction

ExecCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/ExecCommand.java

@Command("exec")
@TxIgnore
public class ExecCommand implements DBCommand {

  @Override
  public RedisToken execute(Database db, Request request) {
    Option<TransactionState> transaction = getTransactionIfExists(request.getSession());
    if (transaction.isPresent()) {
      DBServerContext server = getClauDB(request.getServerContext());
      List<RedisToken> responses = new ArrayList<>();
      for (Request queuedRequest : transaction.get()) {
        responses.add(executeCommand(server, queuedRequest));
      }
      return RedisToken.array(responses);
    } else {
      return RedisToken.error("ERR EXEC without MULTI");
    }
  }

  private RedisToken executeCommand(DBServerContext server, Request queuedRequest) {
    RespCommand command = server.getCommand(queuedRequest.getCommand());
    return command.execute(queuedRequest);
  }

  private Option<TransactionState> getTransactionIfExists(Session session) {
    return session.removeValue("tx");
  }
}

• ExecCommand实现了DBCommand接口，其execute方法先通过getTransactionIfExists获取transaction，若transaction不存在则报错，存在的话则遍历transaction的queuedRequest，挨个执行executeCommand(server, queuedRequest)

DiscardCommand

claudb-1.7.1/src/main/java/com/github/tonivade/claudb/command/transaction/DiscardCommand.java

@Command("discard")
@TxIgnore
public class DiscardCommand implements DBCommand {

  private static final String TX_KEY = "tx";

  @Override
  public RedisToken execute(Database db, Request request) {
    removeTransactionIfExists(request.getSession());

    return RedisToken.responseOk();
  }

  private Option<TransactionState> removeTransactionIfExists(Session session) {
    return session.removeValue(TX_KEY);
  }
}

• DiscardCommand实现了DBCommand接口，其execute方法执行removeTransactionIfExists(request.getSession())

小结

claudb transaction相关的command有MultiCommand、ExecCommand、DiscardCommand

doc

• transaction