Question

I’m curious whether this is a possibility. I have a stored procedure which Inserts and then retrieves the last insert id. What if 2 users both use the procedure at the same time, is something like this possible?

 User 1
             User 2
 Insert 1
             Insert 2
 GetsLastid 2
             GetsLastid 2

Could the 2 calls of the stored procedure interlace the sequence of the insert queries? Or will one take lead?

Thank you!

Answer 1

That’s not a problem. From the fine manual:

The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by the function to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own.

So the last_insert_id() value is always per-session (AKA connection) and you have two sessions in play, the can’t interfere with each other’s last_insert_id() values.

That said, it is a good idea to grab the last_insert_id() value and store it in a variable as soon after the INSERT as possible. If you do something else that does an INSERT behind your back — say you call another procedure that has logging added two months down the road and that logging does an INSERT — you will lose the last_insert_id() value that you want.