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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
Message-ID: 200705301803.24623.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg,

> 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

Josh Berkus
PostgreSQL @ Sun
San Francisco

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