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Re: Bufer cache replacement LRU algorithm?

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Kenneth Marshall" <ktm(at)rice(dot)edu>, "Mladen Gogala" <mladen(dot)gogala(at)vmsinfo(dot)com>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Bufer cache replacement LRU algorithm?
Date: 2010-11-03 17:09:42
Message-ID: 4CD151060200002500037206@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-performance
Kenneth Marshall <ktm(at)rice(dot)edu> wrote:
> On Wed, Nov 03, 2010 at 12:35:33PM -0400, Mladen Gogala wrote:
>> Where can I find the documentation describing the buffer
>> replacement policy? Are there any parameters governing the page
>> replacement policy?
 
> You would need to check the mailing lists. The release notes
> have it as being a clock sweep algorithm starting in version
> 8. Then additional changes were added to eliminate the cache
> blowout caused by a sequential scan and by vacuum/autovacuum.
> I do not believe that there are any parameters available other
> than total size of the pool and whether sequential scans are
> synchronized.
 
The background writer settings might be considered relevant, too.
 
Also keep in mind that PostgreSQL goes through the OS cache and
filesystems; the filesystem choice and OS settings will have an
impact on how that level of caching behaves.  Since there is often
much more cache at the OS level than in PostgreSQL shared buffers,
you don't want to overlook that aspect of things.
 
-Kevin

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