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Re: effective_cache_size less than shared_buffers

From: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: effective_cache_size less than shared_buffers
Date: 2009-02-26 01:33:20
Message-ID: 1235612000.24423.44.camel@jd-laptop.pragmaticzealot.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, 2009-02-25 at 17:04 -0800, Josh Berkus wrote:
> Joshua D. Drake wrote:
> > On Wed, 2009-02-25 at 17:21 -0600, Kevin Grittner wrote:
> >> Should we log a warning at startup when effective_cache_size is less
> >> than shared_buffers?
> > 
> > I would say no. Although I could see an argument for the default
> > effective_cache_size always being the same size as shared_buffers.
> 
> That's certainly not what we've meant historically by ECS.  Generally 
> it's been the size of shared_buffers *and* the FS cache.  If it were 
> just the size of shared_buffers, then we wouldn't need a 2nd setting, 
> would we?

We can't determine the size of the FS cache. We can determine the size
of the shared_buffers. The idea here is to eliminate one of those by
default PostgreSQL is slow issues. Since we are already using X amount
of shared_buffers we know we have at least X amount of cache.

Sincerely,

Joshua D. Drake




> 
> --Josh
> 
> 
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