Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > "Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx> writes: >> We've seen a lot of those lately -- Index Scan Backward >> performing far worse than alternatives. > > It's not clear to me that that has anything to do with Tim's > problem. It certainly wouldn't be 20000x faster if it were a > forward scan. Well, that's one way of looking at it. Another would be that the slower plan with the backward scan was only estimated to be 14.5% less expensive than the fast plan, so a pretty moderate modifier would have avoided this particular problem. The fact that the backward scan mis-estimate may be combining multiplicatively with other mis-estimates doesn't make it less important. -Kevin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
