Tom Lane <t...@sss.pgh.pa.us> wrote: > "Kevin Grittner" <kevin.gritt...@wicourts.gov> 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
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