in order to prevent deadlocks, I locked my program sequentially. Such as the order of oa--as-aa. But since I found that the data did not exist when I got the OA, I first new, and then lock it. The result is the new oa- lock, the oa-new as- lock, the as-new aa- lock, the aa lock. But if it goes on like this, there will be a deadlock. What"s the reason? (oa and as locks use exclusive locks, while aa locks use shared locks)

I do this by adding MySQL row-level locks, for update and in share mode, without locking to the same variable.