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Re: FreeBSD config

From: "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>
To: Shridhar Daithankar <shridhar(at)frodo(dot)hserus(dot)net>
Cc: Dror Matalon <dror(at)zapatec(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: FreeBSD config
Date: 2004-02-27 15:33:40
Message-ID: Pine.LNX.4.33.0402270831490.13785-100000@css120.ihs.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, 27 Feb 2004, Shridhar Daithankar wrote:

> Dror Matalon wrote:
> 
> > Let me try and say it again. I know that setting effective_cache_size
> > doesn't affect the OS' cache. I know it just gives Postgres the *idea*
> > of how much cache the OS is using. I know that. I also know that a
> > correct hint helps performance.
> > 
> > I've read Matt Dillon's discussion about the freebsd VM at
> > http://www.daemonnews.org/200001/freebsd_vm.html and I didn't see him
> > saying that Freebsd uses all the free RAM for disk cache. Would you care
> > to provide a URL pointing to that?
> 
> I don't believe freeBSD yses everything available unlike linux. It is actually a 
> good thing. If you have 1GB RAM and kernel buffers set at 600MB, you are 
> guaranteed to have some mmory in crunch situations.

Linux doesn't work with a pre-assigned size for kernel cache.  
It just grabs whatever's free, minus a few megs for easily launching new 
programs or allocating more memory for programs, and uses that for the 
cache.  then, when a request comes in for more memory than is free, it 
dumps some of the least used buffers and gives them back.  

It would seem to work very well underneath a mixed load server like an 
LAPP box.


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