[Dovecot] zlib plugin

[Curtis Maloney]

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? 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?
> 

Just throwing in my 0.02 currency units...

... obviously, which messages you choose to compress is up to you, and 
should be tuned depending on your system.  Certainly, I wouldn't bother 
compressing anything smaller than 1 allocation block (whatever that is on 
your FS), and even 2, unless your CPU is really idle.

The larger the message, the greater the potential rewards.


PS: Timo... "2x smaller"? ... somehow, I expected better of you :)

-- 
Curtis Maloney
cmaloney at cardgate.net