Pause while selecting INBOX

[Gary Mills]

On Fri, Sep 26, 2008 at 09:19:25AM -0700, Rob Banz wrote:
> 
> On Sep 26, 2008, at 06:44, Gary Mills wrote:
> 
> >We have a moderately sized Cyrus installation with 2 TB of storage
> >and a few thousand simultaneous IMAP sessions.  When one of the
> >backup processes is running during the day, there's a noticable
> >slowdown in IMAP client performance.  When I start my `mutt' mail
> >reader, it pauses for several seconds at `Selecting INBOX'.  That
> >behavior disappears when the backup finishes.
> 
> As always, the answer is probably complicated.

Of course.  I just wanted to know what the usual suspects might be.

> What's your storage backend look like? Some sort of RAID with cache?  
> The backup is very probably blowing out your cache while running,  
> which can manifest itself in ways that will make it look like the  
> performance profile of your storage has taken on a different  
> personality. Especially with respect to writes, since you might  
> usually be blessed with an abundance of write-back cache that's now  
> fighting with all the reads for the backup. Do you have your cyrus  
> partitions mounted with noatime? Your backups could be causing fs  
> write operations that you really don't want.

Our storage backend is four Iscsi LUNs from our Netapp filer.  It will
indeed be RAID with cache.  Yes, the backup certainly would run the
cache, and that may well be the problem.  There will also be a large
memory cache on the IMAP server.  That could be upset as well.  I'll
see if I can find some cache statistics for both places.

`noatime' is also certainly a good idea.  I haven't yet tried it.

-- 
-Gary Mills-    -Unix Support-    -U of M Academic Computing and Networking-