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Re: Query plan degradation 8.2 --> 8.3

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Query plan degradation 8.2 --> 8.3
Date: 2007-05-31 01:03:24
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Lists: pgsql-hackers

> How recently did you check out your 8.3 tree?

It's the snapshot from 5/28, which means it was pulled from CVS on 5/27.  
So, recent.

> 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.

Apparently.  I'll do another build and check.

> It does the right thing if t_s_symb is declared as text instead of
> varchar.  When it's varchar, even setting enable_sort off won't make
> it pick the right plan, which suggests that it fails to recognize that
> the index can match the query's ORDER BY.  I'm guessing I overlooked
> a binary-compatibility case when I rejiggered the handling of PathKeys
> in connection with the NULLS FIRST/LAST stuff.  No time to look deeper
> right now.

Yeah, that looks like the case.  We'll move it to TEXT for the tests right 
now, but I'll make sure we don't forget this bug during beta.  Thanks!


Josh Berkus
PostgreSQL @ Sun
San Francisco

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