SERIALIZABLE is really quite hard to retrofit to existing apps; deadlocks, livelocks, and “it’s slow” show up all over the place when you switch it on.
Definitely recommend starting new codebases with it enabled everywhere.
Do you have examples of deadlocks/livelocks you've encountered using SERIALIZABLE? My understanding was that the transaction will fail on conflict (and should then be retried by the application - wrapping existing logic in a retry loop can usually be done without _too_ much effort)...
I guess I'd say -- I think you're right that you shouldn't (ideally) be able to trigger true deadlocks/livelocks with just serializable transactions + an OLTP DBMS.
That doesn't mean it won't happen, of course. The people who write databases are just programmers, too. And you can certainly imagine a situation where you get two (or more) "ad-hoc" transactions that can't necessarily progress when serializable but can with read committed (ad-hoc in the sense of the paper here: https://cacm.acm.org/research-highlights/technical-perspecti...).
I’m not sure they were _introduced_ by switching to serialised, but it means some processes started taking long enough that the existing possibilities for deadlocks became frequent instead of extremely rare.
Haven’t kept history from the bug tracker back that far, but we definitely hit some pretty awful issues in prod trying to solve race issues with “serialisable”. Big older codebases end up with surprising data access patterns.
Comments
SERIALIZABLE is really quite hard to retrofit to existing apps; deadlocks, livelocks, and “it’s slow” show up all over the place when you switch it on.
Definitely recommend starting new codebases with it enabled everywhere.
Do you have examples of deadlocks/livelocks you've encountered using SERIALIZABLE? My understanding was that the transaction will fail on conflict (and should then be retried by the application - wrapping existing logic in a retry loop can usually be done without _too_ much effort)...
I guess I'd say -- I think you're right that you shouldn't (ideally) be able to trigger true deadlocks/livelocks with just serializable transactions + an OLTP DBMS.
That doesn't mean it won't happen, of course. The people who write databases are just programmers, too. And you can certainly imagine a situation where you get two (or more) "ad-hoc" transactions that can't necessarily progress when serializable but can with read committed (ad-hoc in the sense of the paper here: https://cacm.acm.org/research-highlights/technical-perspecti...).
I’m not sure they were _introduced_ by switching to serialised, but it means some processes started taking long enough that the existing possibilities for deadlocks became frequent instead of extremely rare.
Haven’t kept history from the bug tracker back that far, but we definitely hit some pretty awful issues in prod trying to solve race issues with “serialisable”. Big older codebases end up with surprising data access patterns.