I'm running a really big update on about 150 million rows in an innodb table. It's taken about 3 hours and I can see from undo count that it's about halfway. What I'd like to know if how long it would take to roll back if I killed it. I really can't find any documentation on what happens in this scenario. I know that rollbacks can vary hugely in how long they take depending on what's going on - for example aborting an alter table can happen quickly as it can just drop the temp table it was creating. I'm wondering if there's some similar internal mechanism for the MVCC involved when doing an update - can it just drop the version it's working on?
I have the feeling that killing an update may cause it to go through all the changes made in the undo log in order to restore changed rows, which could take as long as (if not longer) than letting the query complete.
Can anyone point me at definitive docs on precisely what happens during a rollback or query kill?
I have the feeling that killing an update may cause it to go through all the changes made in the undo log in order to restore changed rows, which could take as long as (if not longer) than letting the query complete.
Can anyone point me at definitive docs on precisely what happens during a rollback or query kill?