Re: performance regression with 9.2

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Dave Cramer <pg(at)fastcrypt(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: performance regression with 9.2
Date: 2012-11-15 19:21:13
Message-ID: 20478.1353007273@sss.pgh.pa.us
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Dave Cramer <pg(at)fastcrypt(dot)com> writes:
> This query is a couple orders of magnitude slower the first result is
> 9.2.1, the second 9.1

Thanks for sending me the test case off-list. I found the reason why
I'd not been able to reproduce the problem: the index you're hoping it
will use is declared

"note_sets_parent_id_idx" btree (parent_id) WHERE parent_id IS NOT NULL

Apparently 9.2 is less bright than 9.1 about when it can use a partial
index. I'm not sure where I broke that, but will look.

regards, tom lane

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