[Dovecot] zlib plugin

[Andrey Panin]

On 281, 10 07, 2008 at 03:10:47PM +0300, Timo Sirainen wrote:
> On Tue, 2008-10-07 at 11:38 +0400, Andrey Panin wrote:
> > On 279, 10 05, 2008 at 10:38:02PM +0300, Timo Sirainen wrote:
> > > On Sun, 2008-10-05 at 21:28 +0200, Luuk wrote:
> > > 
> > > > Last but not least, what gain will i have by using this plugin in 
> > > > combination with Maildir, or will it have more impact when mails are 
> > > > stored in mbox.
> > > 
> > > I guess it depends on the size of your mails. With mboxes it can be used
> > > only with read-only archives, so it's not all that useful. With maildir
> > > it can be used transparently with read-write mailboxes. I've no idea
> > > what the performance difference or space improvements are. I guess
> > > that'll also depend on your system.
> > 
> > I use zlib compressed maildirs on my primary server (12000+ users) and it 
> > achieves average compression ratio of 1.8, so if your system is io-bound
> > you can spend some cpu cycles to significantly decrease disk load.
> 
> But is that 1.8 in bytes or disk blocks?

Bytes.

> Or does it make much of a
> difference either way? Does 2x less space per message even matter with
> small messages since most disk I/O probably goes to seeking, so reading
> a single 4 kB message takes pretty much the same time as a 8 kB message?

Yes, for small messages it's not very usefull, but multimegabyte mails are
quite common nowadays and for them compression is a clear win. Also I remember
that load average decreased when I started to use message compression. I have
no real numbers now, but it was noticeable.

-- 
Andrey Panin		| Linux and UNIX system administrator
pazke at donpac.ru		| PGP key: wwwkeys.pgp.net
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