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Re: Query plan degradation 8.2 --> 8.3

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: josh(at)agliodbs(dot)com
Cc: Gregory Stark <stark(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Query plan degradation 8.2 --> 8.3
Date: 2007-05-31 16:59:21
Message-ID: 10062.1180630761@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> 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!

I've applied a patch that fixes this case, but I'm not yet 100%
convinced that there are no other cases where it'll prevent matching
things that should match.  Please test.

			regards, tom lane

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