Re: RT3.4 query needed a lot more tuning with 9.2 than it did with 8.1

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Christoph Berg <christoph(dot)berg(at)credativ(dot)de>
Cc: PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: RT3.4 query needed a lot more tuning with 9.2 than it did with 8.1
Date: 2013-05-06 16:38:48
Message-ID: 1583.1367858328@sss.pgh.pa.us
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Christoph Berg <christoph(dot)berg(at)credativ(dot)de> writes:
> We recently (finally) migrated an Request Tracker 3.4 database running
> on 8.1.19 to 9.2.4. The queries used by rt3.4 are sometimes weird, but
> 8.1 coped without too much tuning. The schema looks like this:

The newer rowcount estimates are much further away from reality:

> Unique (cost=1117.67..1118.46 rows=9 width=1115) (actual time=82.646..85.695 rows=439 loops=1)

> Unique (cost=784205.94..796940.08 rows=145533 width=1061) (actual time=9710.683..9713.175 rows=439 loops=1)

Has the new DB been analyzed? Maybe you had custom stats targets in
the old DB that didn't get copied to the new one?

regards, tom lane

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