Do PDO transactions until all other transactions are completed?

Question

If I am right, PDO transactions are not really transactions: they just disable auto-commands (see the documentation ).

So, if I have a transaction A that deletes a row and a transaction B that modifies the same row, the following may happen.

• Transaction A starts and disables auto-update.
• Transaction B starts and disables auto-update.
• Transaction A deletes a row.
• Transaction B modifies the same row.
• Transaction A completes and commits the changes.
• Transaction B completes and commits the changes.

But in step 6, the row was already deleted in step 5. What will happen?

Also, how can I ensure that transaction B is locked until transaction A? FYI, I am using PDO with mysql with innoDB.

Thanks.

Answer 1

As @eggyal noted, transactions can occur simultaneously, but stat DELETE puts an exclusive lock on the line until the transaction is completed, so transaction B will be automatically locked in step 4 until transaction A is committed. The exclusive blocking block writes and also reads.