[Dovecot] Large folders and timeouts

[Fran Fabrizio]

I have been having persistent issues with server timeouts on operations 
on large folders on our Dovecot install (1.0beta2 RPM that came with 
Fedora Core 5).  Some observations from today...

I have a Maildir folder with 38,000 messages (it is my Spam folder, 
naturally :-).  In Thunderbird 1.5.0.2, if I click on that folder, it 
slowly but steadily downloads the headers and after 3-4 minutes, shows 
me the contents.  So far, so good.  If I then select all the messages 
and click Delete to delete them, that operation times out after about 1 
minute.  If I then click on my Trash folder after some number of minutes 
has passed, I see that those messages are now both in my Trash and in 
the original folder - I believe this is because Thunderbird first asks 
for a COPY over to Trash, and then asks for a STORE +FLAG \\Deleted on 
the copy that is still in the original folder.  It appears that the COPY 
commands are working but the STORE commands are not since the connection 
is timing out before they run.

I thought I'd try on another mail client, so I tried Squirrelmail.  I 
set it to show 1000 messages per page.  It does this just fine.  Then I 
set it to 4,000 messages per page.  Then I click on a folder with 12,000 
messages, and I get this:

ERROR: Connection dropped by IMAP server.
Query: SORT (ARRIVAL) ISO-8859-1 ALL

My questions are 1. what is the likely cause? and 2. will upgrading to a 
newer beta address any of this?  I'd prefer to wait until FC5 has an 
updated RPM if possible.  Our mail is stored on an NFS store.  (I know 
NFS is slow and that this might be part of the cause.)  However, it 
seems that the timeouts I am having are more related to times when there 
is no data flowing between the server and client.  Note that the 
timeouts happened when the server was doing a COPY and when the server 
was doing a SORT but not when the client was downloading 38,000 
headers.  I'm just at a loss for what to look into next.  I don't want 
to just say "NFS is slow" and live with it if this really has some other 
cause.  :-)

So, anyone have any thoughts as to other possible causes?

Thunderbird has no option for setting the length of timeout from the 
client side, so there's nothing I can do from that end.

Thanks,
Fran





-- 
Fran Fabrizio
Senior Systems Analyst
Department of Computer and Information Sciences
University of Alabama at Birmingham
http://www.cis.uab.edu/
205.934.0653