MySQL会自动释放事务回滚时的连接吗？

Question

我以前在某人的代码里发现过这个。正如标题所说，调用rollback是否将连接释放回池中？

样品

router.post('/test', async (req, res, next) => {
  const connection = await database.getConnection();
  try {
    try {
      await connection.query(`INSERT INTO listings(num) VALUES ('1')`);
      await connection.query(`INSERT INTO listings(num) VALUES ('2')`);
      await connection.query(`INSERT INTO listings(num) VALUES ('3')`);
      await connection.commit();
    } finally {
      // all queries have executed, we can release the connection.
      connection.release();
    }
  } catch (err) {
    // will this also release the connection?
    await connection.rollback();
  }
});

更新

router.get('/x', async (req, res, next) => {
  try {
    const connection = await database.getConnection();
    try {
      await connection.query(`INSERT INTO listings(num) VALUES (1)`);
      await connection.query(`INSERT INTO listings(num) VALUES (2)`);
      await connection.query(`INSERT INTO listings(num) VALUES (3)`);
      await connection.commit();
    } catch (err) {
      // something happened roll back
      await connection.rollback();

      // due to this finally becomes unreachable?
      throw err;
    } finally {
      // all queries have executed, we can release the connection.
      connection.release();
    }
  } catch (err) {
    // error
  }
});

Answer 1

你发布的代码很奇怪，不是说不正确。没有任何理由使用两个嵌套的try/catch块。它们的使用方式违背了finally的目的。

在退出try/catch构造之前，执行finally块中的代码，无论它是如何完成的。

它将在try块中的代码执行之后执行，如果它没有引发任何异常，或者在catch块执行之后执行，如果引发了异常（由try块中的代码引发）。如果catch块中的代码抛出异常，它甚至会执行（这种异常在此级别无法捕获，它会被调用此函数的代码中最内部的try/catch块捕获。）

您的代码应该如下所示：

router.post('/test', async (req, res, next) => {
  const connection = await database.getConnection();

  try {
    await connection.query(`INSERT INTO listings(num) VALUES ('1')`);
    await connection.query(`INSERT INTO listings(num) VALUES ('2')`);
    await connection.query(`INSERT INTO listings(num) VALUES ('3')`);
    await connection.commit();
  } catch (err) {
    await connection.rollback();
  } finally {
    // all queries have executed, we can release the connection.
    connection.release();
  }
});

它在结束时释放连接，无论事务以何种方式结束。