当Golang程序在执行数据库事务时终止时，它可以回滚吗？

Question

Assuming a MariaDB compatible database (AWS Aurora RDS) with default settings, which includes autocommit enabled, if a Lambda function was terminated after three seconds doing a transaction that takes more than five seconds, e.g.

  tx, err := h.db.Begin()
  if err != nil {
      log.WithError(err).Error("failed to start transaction")
  }
  res, execErr := tx.Exec(fmt.Sprintf("UPDATE testtable SET val = %d WHERE id = 1; SELECT SLEEP(5.5);", time.Now().Unix()))
  if execErr != nil {
      log.WithError(err).Error("rolling back")
      err = tx.Rollback()
      if err != nil {
          log.WithError(err).Error("failed to roll back")
      }
  }
  if err := tx.Commit(); err != nil {
      log.WithError(err).Error("failed to commit")
  }

What would one assume the result to be? The transaction would have not been committed?

I am using Go MySQL Driver v1.3.0-84-g6be42e0 btw. I also made a video showing my results, but I am wondering if it is right since I don't understand how the driver could have executed rollback.

Answer 1

The transaction SQL does not commit. What I believe happens with a <= 5s timeout:

1. BEGINs transaction
2. Executes the SQL synchronously
3. MySQLd detects the client disconnected via a TCP FIN
4. MySQLd automatically rolls back since it doesn't see the Commit

A tweet reply from one of the Golang MySQL driver maintainers:

mysqld receives TCP FIN packet when Go client is terminated.
Even though Go client exits uncleanly, OS (Linux kernel, etc) sends TCP FIN or TCP RST. So mysqld can know client is gone.— INADA Naoki (@methane) December 4, 2018