[imp] Hack concept - IMAP speedup

Paul Reilly pareilly at tcd.ie
Wed Sep 8 15:26:08 PDT 2004

Look at Dovecot IMAP - www.dovecot.org

We switched from Courier to Dovecot and noticed a huge performance
boost. Mainly because it keeps indexes.


On Wed, 8 Sep 2004, Ross Becker wrote:

> Just throwing this out, I'm really not certain as to which organizations
> I should be talking to about this, but Horde/IMP seems as good as any.
> Currently, free IMAP servers which are capable of webmail backend is bad
> for any organization which can allow large folders. The primary reason
> is that maildir (and maildir++) has no indexing at all. This means that
> to sort a folder, you have to open every message, read the headers, suck
> out the one(s) you need, and transform them into sortable format.  Once
> you've read every message, then you can sort.  This leads to woeful
> performance.  On a Pentium 4 with 800mhz memory bus, I clocked
> Courier-IMAP taking ~14 seconds to sort a 12.5k message folder by date.
> Clearly, for a webmail system, you want the server to be able to sort
> the messages fast, because all sorts will happen on the server.
> I'm looking at hacking (probably) procmail, and Courier-IMAP to maintain
>   fixed-length record files containing the message headers needed to
> support standard search and sort operations.  Not indexes, as that would
> require putting sorting code into the MDA (procmail).  At a wild guess,
>   this should provide at least an order of magnitude improvement in
> search and sort times.
> The ugliness is figuring out if procmail is the best delivery agent to
> add this hack to (I'm leaning there because of it's excellent support
> for delivery recipes & filters) and if there's any way this could be
> done in such a fashion that it could go into permanent project code.
> If anyone else here is interested in this hack, has thoughts, or
> whatever- I'm all ears.
> Cheers
>     Ross
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