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Re: performance penalty between Postgresql 8.3.8 and 8.4.1

From: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
To: Thom Brown <thombrown(at)gmail(dot)com>
Cc: "Schmitz, David" <david(dot)schmitz(at)harman(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-performance(at)postgresql(dot)org
Subject: Re: performance penalty between Postgresql 8.3.8 and 8.4.1
Date: 2009-12-08 12:12:04
Message-ID: 4B1E4294.6020703@postnewspapers.com.au (view raw or flat)
Thread:
Lists: pgsql-performance
On 8/12/2009 6:11 PM, Thom Brown wrote:

> Your output shows that the xdf_admin_hierarchy tables between versions
> are drastically different.  8.3.8 only contains 1 row, whereas 8.4.1
> contains 84211 rows.

That's just because one of them is doing a nested loop where it looks up 
a single row from xdf_admin_hierarchy via its primary key on each 
iteration. The other plan is doing a hash join on a sequential scan over 
xdf_admin_hierarchy so it reports all the rows at once.

--
Craig Ringer

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