From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | josh(at)agliodbs(dot)com |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Query plan degradation 8.2 --> 8.3 |
Date: | 2007-05-30 23:28:18 |
Message-ID: | 22544.1180567698@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> 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.
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.
regards, tom lane
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