On 11 October 2012 20:43, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> So we have to take the snapshot before you begin execution, but it >> seems that to avoid surprising behavior we also have to take it after >> acquiring locks. And it looks like locking is intertwined with a >> bunch of other parse analysis tasks that might require a snapshot to >> have been taken first. Whee. > > Yeah. I think that a good solution to this would involve guaranteeing > that the execution snapshot is not taken until we have all locks that > are going to be taken on the tables. Which is likely to involve a fair > amount of refactoring, though I admit I've not looked at details. > > In any case, it's a mistake to think about this in isolation. If we're > going to do something about redefining SnapshotNow to avoid its race > conditions, that's going to move the goalposts quite a lot. > > Anyway, my feeling about it is that I don't want 9.2 to have an > intermediate behavior between the historical one and whatever we end up > designing to satisfy these concerns. That's why I'm pressing for > reversion and not a band-aid fix in 9.2. I certainly hope we can do > better going forward, but this is not looking like whatever we come up > with would be sane to back-patch.
Agreed, please revert. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
