[Dovecot] extremely slow delete/move operations?

[John Peacock]

Gregory K. Ruiz-Ade wrote:
> 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...

Same hardware?  Same file sizes?  Same software rarely translates to 
equivalent performance unless the other parameters are also constant. 
NFS access in general and mbox files in particular degrade with filesize 
rather rapidly in my experience.  I'm not saying maildir is perfect; 
hugh numbers of files in a single directory will eventually show up 
inefficiencies in the filesystem caching of directory entries.

>> 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.

I misunderstood and thought that the user folders were on the NetApp 
(though I went back and re-read your original posting and you were clear 
that only some were).  But, NFS mounts, even if they are local, AFAIK 
still means NFS filelocking and the associated performance drag.  You 
might check out this page:

	http://nfs.sourceforge.net/#section_b

and see whether your NFS options are tuned for performance (in 
particular what the setting of subtree_check is).

> 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

Don't discount this option until you try it; the TBird 1.5 upgrade is 
very painless (in my experience) and takes the existing profile 
unchanged.  That's up to you, though.  I was just pointing out that 
there are any number of places where the performance can drag.

John

-- 
John Peacock
Director of Information Research and Technology
Rowman & Littlefield Publishing Group
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