Inconsistent expunge performance

[Nels Lindquist]

Hi there.

Since upgrading to Cyrus IMAP 2.2.x, I've noticed some fairly extreme 
performance degradation when it comes to expunging deleted mail.

This behaviour is inconsistent from folder to folder, but quite 
consistent WRT an individual folder.

I haven't been able to find much of a pattern involving numbers of 
messages, ages of folders, etc.  Some folders complete an expunge 
almost immediately, some take nearly five minutes while generating 
quite a high load on the server.

Is there some explanation for this?  I've gone through the Wiki 
regarding DB backends and I seem to have everything set up according 
to the recommendations.  Which database is most directly impacted by 
an "expunge" operation?  Is there anything I can do to alleviate this 
problem?  I tried putting imap/proc on tmpfs as discussed in the 
performance documentation, but it didn't make any difference for the 
expunge behaviour (though it would seem opening a folder is slightly 
faster).

The server isn't very heavily loaded; there are less than 200 
mailboxes and usually less than 20 concurrent users.  IO shouldn't be 
a problem; the disk is 10,000 RPM SCSI.

Any advice would be greatly appreciated!

----
Nels Lindquist <*>
Information Systems Manager
Morningstar Air Express Inc.

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