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another 8.1->8.4 regression

From: Ben Chobot <bench(at)silentmedia(dot)com>
To: PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org>
Subject: another 8.1->8.4 regression
Date: 2010-02-16 21:29:16
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
I'm having problems with another one of my queries after moving from 8.1.19 to 8.4.2. On 8.1.19, the plan looked like this:

That runs pretty well. On 8.4.2, the same query looks like this:

If I turn off mergejoin and hashjoin, I can get 8.4.2 to spit out this:

...which it thinks is going to suck but which does not. 

The query and relevant table definitions are here:

Any suggestions? I'm guessing the problem is with the absurd over-estimation on the nested loop under the sort node, but I'm not sure why it's so bad. 


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