Date: Tue, 4 Oct 2005 15:57:20 -0500
From: "Jim C. Nasby" <jnasby@pervasive.com>
To: Stefan Weiss <spaceman@foo.at>
Cc: pgsql-performance@postgresql.org
Subject: Re: Is There Any Way ....
Message-ID: <20051004205719.GY40138@pervasive.com>
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On Tue, Oct 04, 2005 at 12:31:42PM +0200, Stefan Weiss wrote:
> On 2005-09-30 01:21, Lane Van Ingen wrote:
> >   (3) Assure that a disk-based table is always in memory (outside of keeping
> > it in
> >       memory buffers as a result of frequent activity which would prevent
> > LRU
> >       operations from taking it out) ?
> 
> I was wondering about this too. IMO it would be useful to have a way to tell
> PG that some tables were needed frequently, and should be cached if
> possible. This would allow application developers to consider joins with
> these tables as "cheap", even when querying on columns that are not indexed.
> I'm thinking about smallish tables like users, groups, *types, etc which
> would be needed every 2-3 queries, but might be swept out of RAM by one
> large query in between. Keeping a table like "users" on a RAM fs would not
> be an option, because the information is not volatile.

Why do you think you'll know better than the database how frequently
something is used? At best, your guess will be correct and PostgreSQL
(or the kernel) will keep the table in memory. Or, your guess is wrong
and you end up wasting memory that could have been used for something
else.

It would probably be better if you describe why you want to force this
table (or tables) into memory, so we can point you at more appropriate
solutions.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461