"Dan Boeriu" <dan.boe...@roost.com> writes: > Attached is the reproducible test case - I was able to reproduce the problem > on 32 and 64 bit 8.3.6 and 8.4.0 RedHat 5.3 kernel 2.6.18-128.1.16.el5 #1 SMP
I looked at this a bit. It's the same issue discussed at http://archives.postgresql.org/pgsql-bugs/2008-09/msg00045.php namely, that the second update finds itself trying to update a large number of tuples that were already updated since its snapshot was taken. That means it has to re-verify that the updated versions of those tuples meet its WHERE qualification. That's done by a function EvalPlanQual that's pretty darn inefficient for complex queries like this one. It's essentially redoing the join (and recomputing the whole sub-SELECT) for each row that needs to be updated. Someday I'd like us to redesign that mechanism, but don't hold your breath ... regards, tom lane -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
