[Dovecot] More Benchmarks, and a question about indexing

[Timo Sirainen]

On Tue, 2004-02-17 at 02:47, Anthony Wendell Kay wrote:
> We are thinking of converting to Dovecot to lighten our I/O load. I have done
> some performace tests comparing UW-IMAP to Dovecot when using mbox format if
> anyone is interested. They primarily examine the I/O improvements that can be
> gained from using Dovecot over UW when staying with mbox format:
> 
> http://whizzo.uoregon.edu/public/src/mailperf/results.html

Good testing. I was going to do something similiar myself, but only for
the next release which will have rewritten index and mbox code. I know
the current mbox code is really slow and buggy in some situations.

I've however heard of getting much larger performance benefits when
switching from UW-IMAP. I think they had mostly Outlook/OE clients.
Drops from average 20MB/s disk I/O to few kB/s.

> Anyway, we are stuck with the mbox format for the forseeable future, and I
> noticed how hard hitting Dovecot is on initial access to a large mailbox, so we
> need a way to pre-create some of those indexes. I saw in the docs that such an
> indexer has been planned, but does anyone have a hack for doing it now?

This, and POP access will work better in next version too. Currently
Dovecot goes and stores all kinds of cached data to index files even if
client never uses them. This will change so that data is stored only
when client actually asks for it which I think makes opening large
mailboxes almost as fast as UW-IMAP (small hit for writing 200-500kB
indexes per 10000 mails).

I'll also create Dovecot LDA which is able to update the indexes
directly while storing the mail, that should help some too.

Anyway, back to coding. I hope to get it usable soon and committed to
CVS. Before that I'm pretty unresponsive..

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