We're able to utilize ~ 4GB of cache on a 32bit installation of
Cyrus/Postfix (we're using ext3 - dunno if it has a different cache
limitation compared to reiser). This installation serves ~15k mailboxes
and has between 250 and 500 active POP/IMAP sessions at any given time.
Unfortunately, we do not currently make use of the full 24GB RAM in
these machines. Perhaps with a 64 bit installation would resolve that...
anyway, here are the mem stats.
----
total used free shared buffers cached
Mem: 24906720 9973956 14932764 0 298412 4513164
-/+ buffers/cache: 5162380 19744340
Swap: 1052248 0 1052248
----
If we are able to make use of 10GB (half of which is cache) on a
similarly loaded machine, you should be able use just as much (if not
more on a 64bit installation).
--Blake
-------- Original Message --------
Subject: Does Cyrus benefit greatly from increased FS buffer cache?
From: John Widera <jwidera@xxxxxxxxxx>
To: info-cyrus@xxxxxxxxxxxxxxxxxxxx
Cc: data center <datacenter@xxxxxxxxxx>
Date: Tuesday, April 14, 2009 3:14:39 PM
> Hi,
>
> Last week we posted to the list for info about running Cyrus on 64-bit
> RHEL. But we also needed to ask a more direct question about caching,
> though, and didn't. So we are now...
>
> That q. is, does Cyrus actually benefit from large amounts of memory in an
> environment with just a few thousand users ( <1000 simultaneous sessions)
> and, say, up to 750GB of mail spool?
>
> Our plan is to throw 12-16GB at it, with the purpose of vastly increasing
> the FS buffer cache (and decreasing I/O). Or, will that just be a waste
> of RAM?
>
> Some indications are that, yes, it does improve performance notably:
>
> http://blog.fastmail.fm/2007/09/21/reiserfs-bugs-32-bit-vs-64-bit-kernels-cache-vs-inode-memory/
>
> Anyone have any specific thoughts? Is there any other benefit we might
> see from large memory allocation in 64-bit architecture?
>
> Thanks,
>
> John Widera
> Oakton Community College
> Des Plaines and Skokie, IL
>
> ----
> Cyrus Home Page: http://cyrusimap.web.cmu.edu/
> Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
> List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
>
----
Cyrus Home Page: http://cyrusimap.web.cmu.edu/
Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
