From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: pgsql-performance@postgresql.org
Subject: Re: Mount database on RAM disk?
Date: Fri, 8 Jul 2005 10:22:01 -0700
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Cc: Stuart Bishop <stuart@stuartbishop.net>
References: <42CDD7B8.6050109@stuartbishop.net>
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Stuart,

> I'm putting together a road map on how our systems can scale as our load
> increases. As part of this, I need to look into setting up some fast
> read only mirrors of our database. We should have more than enough RAM
> to fit everything into memory. I would like to find out if I could
> expect better performance by mounting the database from a RAM disk, or
> if I would be better off keeping that RAM free and increasing the
> effective_cache_size appropriately.

If you're accessing a dedicated, read-only system with a database small 
enough to fit in RAM, it'll all be cached there anyway, at least on Linux 
and BSD.   You won't be gaining anything by creating a ramdisk.

BTW, effective_cache_size doesn't determine the amount of caching done.  It 
just informs the planner about how much db is likely to be cached.  The 
actual caching is up to the OS/filesystem.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco