Re: Overhauling GUCS

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>, Greg Smith <gsmith(at)gregsmith(dot)com>, Andreas Pflug <pgadmin(at)pse-consulting(dot)de>, "Decibel!" <decibel(at)decibel(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org, Josh Berkus <josh(at)agliodbs(dot)com>
Subject: Re: Overhauling GUCS
Date: 2008-06-11 23:40:36
Message-ID: 200806112340.m5BNea602628@momjian.us
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Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> > The second idea is the idea of having one parameter depend on another.
> > Not only could we do that for some of our existing parameters, but we
> > could have pseudo-parameters like concurrent_queries, memory_usage, and
> > extra_disk_space that could be at the top of postgresql.conf and then
> > affect the other settings.
>
> We have tried to do that in the past, and it didn't work well *at all*.

We have? When?

> The idea has a fundamental logical flaw, which is that it's not clear
> which parameter wins if the user changes both.

Yes, you could get into problems by having variable dependency loops,
but I see no way to easily improve configuration without it.

My idea was to have:

memory_usage = 128MB ## pseudo-parameter
shared_buffers = $memory_usage * 0.75

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +

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