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Re: IN list processing performance (yet again)

From: Dave Tenny <tenny(at)attbi(dot)com>
To: Bruno Wolff III <bruno(at)wolff(dot)to>
Cc: Andreas Pflug <Andreas(dot)Pflug(at)web(dot)de>,pgsql-performance(at)postgresql(dot)org
Subject: Re: IN list processing performance (yet again)
Date: 2003-05-28 20:01:34
Message-ID: 3ED5159E.2050407@attbi.com (view raw or flat)
Thread:
Lists: pgsql-performance
Bruno Wolff III wrote:

>On Wed, May 28, 2003 at 14:08:02 -0400,
>  Dave Tenny <tenny(at)attbi(dot)com> wrote:
>  
>
>>Andreas Pflug wrote:
>>
>>I'm reminded to relay to the PostgreSQL devos that I might be able to do 
>>more in the  join or subquery department if
>>PostgreSQL had better performing MAX functions and a FIRST function for 
>>selecting rows from groups.
>>("Performing" being the operative word here, since the extensible 
>>architecture of PostgreSQL currently makes for poorly
>>performing MAX capabilities and presumably similar user defined 
>>aggregate functions).
>>    
>>
>
>Have you tried replacing max with a subselect that uses order by and limit?
>  
>

I'm uncertain how that would work, since somewhere in there I still need 
to elaborate on the
1000 items I want, and they're not necessarily in any particular range, 
nor do they bear any
contiguous group nature.

Also, IN (subquery) is a known performance problem in PGSQL, at least if 
the subquery is going to return many rows.
It's too bad, since I'm rather fond of subqueries, but I avoid them like 
the plague in PostgreSQL.

Perhaps I don't understand what you had in mind.

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