IMAP group performance on old groups.

[Daniel Pittman <daniel@rimspace.net>]

G'day.

I use the Cyrus IMAP server for managing my mail.  For the longest time,
I did this by downloading mail from it and pushing it into nnml on my
laptop.

Recently, though, I have moved to using IMAP and storing all the mail on
the server, with nnmiap.  This works great, but performance on my INBOX
is a bet less than stellar.

It takes around 10 seconds on a P4M-1.7 to "Update info" on the group. 
The profile for entering the group is:

Function Name                         Ticks/Total %Usage Calls GC-Usage/  Total
===========================================/===== ====== ===== ========/=======
sort                                   2224/ 4278 40.792     8        0/  37120
(profile overhead)                     2073/ 2073 38.023                       
(in garbage collection)                 417/  417  7.649     3                 
<                                       148/  152  2.715 6591479                 
gnus-compress-sequence                  107/  107  1.963     8     4308/   4308
gnus-uncompress-range                   103/  143  1.889     2  8304768/8304768
delq                                     54/   54  0.990   264                 
append                                   39/   78  0.715    56  8306184/8306184
copy-sequence                            37/   90  0.679    75  8308304/8308304
kill-all-local-variables                 31/   33  0.569   141        0/     72


Looking at this, and the fact that the first real article number in the
group is 658436, makes me think that processing the group is slow
because Gnus uncompresses, compresses and processes numbers from 1
through 658436 at some point in the process.

Is there any easy way to improve performance here?

Also, is this a known issue, or should I start looking deeper into the
nnimap code to find the exact cause of this?

Thanks,
        Daniel