On Mon, Aug 22, 2011 at 10:25 PM, Robert Haas <robertmh...@gmail.com> wrote:
> I've been giving this quite a bit more thought, and have decided to > abandon the scheme described above, at least for now. I liked your goal of O(1) snapshots and think you should go for that. I didn't realise you were still working on this, and had some thoughts at the weekend which I recorded just now. Different tack entirely. > Heikki has made the suggestion a few times (and a few other people > have since made somewhat similar suggestions in different words) of > keeping an-up-to-date snapshot in shared memory such that transactions > that need a snapshot can simply copy it. I've since noted that in Hot > Standby mode, that's more or less what the KnownAssignedXids stuff > already does. I objected that, first, the overhead of updating the > snapshot for every commit would be too great, and second, it didn't > seem to do a whole lot to reduce the size of the critical section, and > therefore probably wouldn't improve performance that much. But I'm > coming around to the view that these might be solvable problems rather > than reasons to give up on the idea altogether. Sounds easy enough to just link up KnownAssignedXids and see... -- 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
