Inconsistent expunge performance

[Nels Lindquist]

Sorry for the long delay in replying; things have been a wee bit 
hectic.

On 18 Aug 2004 at 19:42, Ken Murchison wrote:

> Nels Lindquist wrote:
> 
> > Since upgrading to Cyrus IMAP 2.2.x, I've noticed some fairly extreme 
> > performance degradation when it comes to expunging deleted mail.
> 
> Which 2.2.x version?

It was version 2.2.3.  I've now upgraded to 2.2.8, but it didn't seem 
to make much difference.

> > 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.
> 
> Sounds like the folder may be corrupt, you are deleting a *lot* of 
> messages, or you may be running 2.2.4-2.2.7.

How would I check for/recover from folder corruption?  Some of the 
folders have lots of messages in them, though that doesn't seem to be 
a predictor for whether the expunge is slow or not (the same 
behaviour has been observed in folders with few messages).  As for 
the number of messages I'm deleting, in the affected folders it's 
slow even if I'm trying to expunge only a single message.

> > 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? 
> 
> None.  The only files involved in an expunge are cyrus.index, 
> cyrus.cache, the message files, and the quota file (which in 2.2.4+ uses 
> the cyrusdb interface).

I don't believe there are even quotas defined for the affected 
folders.

>  >  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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