PDO事务是否会阻塞，直到所有其他事务都被提交？

Question

If I am correct, PDO transactions are not really transactions: they merely turn off autocommits (See documentation ).

So if I have a transaction A which deletes a row and transaction B which modifes the same row, the following could happen.

1. Transaction A starts and turns off autocommit.
2. Transaction B starts and turns off autocommit.
3. Transaction A deletes a row.
4. Transaction B modifies the same row.
5. Transaction A finishes and commits changes.
6. Transaction B finishes and commits changes.

But at step 6, the row has been already deleted in step 5. What would happen?

Also, how can I make sure to let Transaction B to block until Transaction A is committed? FYI, I am using PDO with mysql with innoDB.

Thank you.

Answer 1

As @eggyal pointed out, transactions can occur at the same time but a DELETE statment puts an exclusive lock on the row until the transaction is committed, so Transaction B will automatically block at step 4 until Transaction A is committed. An exclusive lock block all writes and also reads.