MySQL table with AUTO_INCREMENT primary id does not release the number after a rollback

Question

I have a table with bills. Every bill has an id that comes from the DB after I insert a new record. The field is an INTEGER with AUTO_INCREMENT set.

If I insert a new re

Answer 1

For concurrency reasons, the auto increment value cannot "rollback" with your transaction. If another process had inserted records while your transaction was in process, you'd risk a collision with their IDs later.

As an example, let's say your transaction in process "A" grabs IDs 1,2 and 3. Another process "B" runs and gets IDs 4 and 5. If the identity rolled back with your transaction and the next process "C" needed 5 IDs, it would get 1,2,3,4,5 but 4 and 5 were already taken by process "B".