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Re: performance penalty between Postgresql 8.3.8 and 8.4.1

From: "Schmitz, David" <david(dot)schmitz(at)harman(dot)com>
To: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Thom Brown<thombrown(at)gmail(dot)com>
Cc: 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 13:27:14
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Hi Craig,

that is exactly the problem postgresql 8.4.1 does not consider the primary key but instead calculates 
a hash join. This can only result in poorer performance. I think this is a bug.



>-----Urspr√ľngliche Nachricht-----
>Von: Craig Ringer [mailto:craig(at)postnewspapers(dot)com(dot)au] 
>Gesendet: Dienstag, 8. Dezember 2009 13:12
>An: Thom Brown
>Cc: Schmitz, David; Andres Freund; pgsql-performance(at)postgresql(dot)org
>Betreff: Re: [PERFORM] performance penalty between Postgresql 
>8.3.8 and 8.4.1
>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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