From: Josh Berkus <josh@agliodbs.com>
To: pgsql-hackers@postgresql.org
Cc: Anjan Kumar. A. <anjankumar@cse.iitb.ac.in>
Cc: pgsql-chat@postgresql.org
Cc: pgsql-benchmarks@postgresql.org
Cc: pgsql-docs@postgresql.org
Subject: Re: [HACKERS] Please Help: PostgreSQL Query Optimizer
Date: Mon, 12 Dec 2005 22:47:21 -0800
Message-ID: <200512122247.21560.josh@agliodbs.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0512120139080.6920@nsl-33.cse.iitb.ac.in>
References: <Pine.LNX.4.61.0512111610320.4525@nsl-33.cse.iitb.ac.in>
<200512111126.18566.josh@agliodbs.com>
<Pine.LNX.4.61.0512120139080.6920@nsl-33.cse.iitb.ac.in>
Anjan,
> But, in PostgreSQL all costs are scaled relative to a page fetch. If we
> make both sequential_page_fetch_cost and random_page_cost to "1", then we
> need to increase the various cpu_* paramters by multiplying the default
> values with appropriate Scaling Factor. Now, we need to determine this
> Scaling Factor.
I see, so you're saying that because the real cost of a page fetch has
decreased, the CPU_* costs should increase proportionally because relative to
the real costs of a page fetch they should be higher? That makes a sort of
sense.
The problem that you're going to run into is that currently we have no
particularly reason to believe that the various cpu_* costs are more than
very approximately correct as rules of thumb. So I think you'd be a lot
better off trying to come up with some means of computing the real cpu costs
of each operation, rather than trying to calculate a multiple of numbers
which may be wrong in the first place.
I know that someone on this list was working on a tool to digest EXPLAIN
ANALYZE results and run statistics on them. Can't remember who, though.
Also, I'm still curious on how you're handling shared_mem, work_mem and
maintenance_mem. You didn't answer last time.
--
Josh Berkus
Aglio Database Solutions
San Francisco
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To: pgsql-benchmarks@postgresql.org
Cc: josh@agliodbs.com, pgsql-hackers@postgresql.org, anjankumar@cse.iitb.ac.in, pgsql-chat@postgresql.org, pgsql-docs@postgresql.org
Subject: Re: [HACKERS] Please Help: PostgreSQL Query Optimizer
In-Reply-To: <200512122247.21560.josh@agliodbs.com>
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