[Dovecot] extremely slow delete/move operations?

[Gregory K. Ruiz-Ade]

John Peacock wrote:
> Those are the two most important pieces of information in your message 
> (IMHO).  mbox is always slower than maildir when the filesize exceeds 
> the operating memory for the server (i.e. it cannot be mmapped).

Well, this is something that I cannot change.  We're stuck with mbox for 
now.  The last time I used dovecot (at my previous job), dovecot 
out-performed UWIMAPd on the same mbox mailboxes, so why it's the other way 
around is beyond me...

> NFS 
> will always be slower than "local" access, even on NetApp's supposed 
> 'high-performance' NFS.  The combination is deadly, since every message 
> stored in Trash requires copying the entire mbox file and appending the 
> new message, then deleting the original and renaming the new file in its 
> place.

The thing is, these mail servers _are_ the local storage for the mail spools 
and home directories.  There is no network involved when dovecot is 
accessing the INBOX or saved mail folders.  Yes, they're "NFS" mounted, but 
this is RHEL4 (linux 2.6.x), and when an NFS share is mounted from the local 
host, it's done as a bind mount, which means local disk access.

> Then there is the additional performance drag caused by Dovecot 
> rewriting the index, as well as Thunderbird (which you should really 
> upgrade to 1.5) keeping its local index up to date.  You can confirm 
> this by emptying your trash folder and seeing if the performance changes 
> (which I am confident it will).

Should I then wonder about turning off Dovecot's indexing?  If that's a 
"performance drag"...

Upgrading Thunderbird may not be so simple, either.  These same clients were 
having much faster response times on a Sun E450 running Solaris 2.8 and 
UWIMAPd with the same logical setup (NFS mail spool and home directories 
mounted from the local system).  Our Windows users can be more easily 
upgraded to later clients right now than our Linux/Unix users

> There are three things you can do to improve performance:
> 
> 1) Upgrade to Dovecot 1.0 stable (or even Beta2);

I wasn't aware there was a 1.0 stable yet.

> 2) Switch to Maildir (instead of mbox);

Not an option.

> 3) Install a SAN (instead of the NFS mounted NAS).

As much as I may wish for it, it's not an option either.  And, I point out 
again, that the mail servers have the necessary filesystems _locally_ 
mounted, by automount, via bind mounts:

-----
gruizade at csefast(pts/22):~ 21 > mount | grep gruizade
/export/homes1/gruizade on /home/gruizade type none (rw,bind)
-----

I will work on testing 1.0 beta2 for now...

Thanks again,

Gregory

-- 
Gregory K. Ruiz-Ade
Sr. Systems Administrator
Computer Science and Engineering
University of California, San Diego
Office: EBU3b 1216
Phone:  (858) 822-2625
E-mail: gkra at ucsd.edu