From: PFC <lists@peufeu.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Volunteer to build a configuration tool
Date: Wed, 20 Jun 2007 09:49:02 +0200
Message-ID: <op.tt7mn0m9cigqcu@apollo13> (raw)
In-Reply-To: <9001.1182323187@sss.pgh.pa.us>
References: <A3AC4FA47DC0B1458C3E5396E685E63302395E53@SAB-DC1.sab.uiuc.edu>
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<Pine.GSO.4.64.0706200040001.7594@westnet.com>
<7621.1182318230@sss.pgh.pa.us>
<Pine.GSO.4.64.0706200224430.16657@westnet.com>
<9001.1182323187@sss.pgh.pa.us>
> To me, the worst catch-22 we face in this area is that we'd like the
> optimizer's choices of plan to be stable and understandable, but the
> real-world costs of queries depend enormously on short-term conditions
> such as how much of the table has been sucked into RAM recently by
> other queries. I have no good answer to that one.
Yeah, there is currently no way to tell the optimizer things like :
- this table/portion of a table is not frequently accessed, so it won't
be in the cache, so please use low-seek plans (like bitmap index scan)
- this table/portion of a table is used all the time so high-seek-count
plans can be used like index scan or nested loops since everything is in
RAM
Except planner hints (argh) I see no way to give this information to the
machine... since it's mostly in the mind of the DBA. Maybe a per-table
"cache temperature" param (hot, warm, cold), but what about the log table,
the end of which is cached, but not the old records ? It's messy.
Still PG does a pretty excellent job most of the time.
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To: pgsql-docs@postgresql.org
Cc: lists@peufeu.com, tgl@sss.pgh.pa.us, gsmith@gregsmith.com, pgsql-performance@postgresql.org
Subject: Re: Volunteer to build a configuration tool
In-Reply-To: <op.tt7mn0m9cigqcu@apollo13>
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