Re: Query plan degradation 8.2 --> 8.3

"Josh Berkus" <josh@agliodbs.com> writes:

> On Wednesday 30 May 2007 15:51, Josh Berkus wrote:
>> I now have a simple test case which shows significant performance
>> degradation on 8.3devel for a specific query, apparenly due to an
>> unnecessary call to Top-N sort.  I've tried to forward the test case to
>> the lists but the package is 3.5m, so I'm putting it on pgFoundry
>> instead:

How recently did you check out your 8.3 tree?

When I run it I get a bitmap index scan which I think might mean you're
suffering from the same problem Tom found and fixed a few days ago. The
planner is finding the bitmap index scan with the sort is the best possible
plan but then discarding that option later leaving it with a suboptimal
choice.

The exact manifestation is somewhat different from what other people saw. iirc
they saw sequential scans when there was an index scan available. But I
suspect it's the same thing going on.

--  Gregory Stark EnterpriseDB          http://www.enterprisedb.com