Tomas Kuliavas wrote:
This evening I set up a test. I used the same Maildir ~850MB in size with 27k messages in my INBOX in each case. I logged into SquirrelMail with each user three times, and took the average number of seconds before the INBOX folder contents appeared.
I think bottleneck is in your filesystem. Compare directory access times
on different filesystems. Find the one that can access directories with
many small files faster.
Case 1: Maildir lives on an ext2 filesystem within a RAID5 set of five disks. This filesystem is then NFS mounted to the IMAP server. Average time to display: 41 seconds.
Case 2: Maildir lives on a reiserfs (Reiser4) filesystem on a RAID0 set of two disks. This filesystem is then NFS mounted to the IMAP server. Average time to display: 64 seconds.
Case 3: Maildir lives on an ext3 filesystem on a RAID0 set of two disks. This filesystem is local to the IMAP server. Average time to display: 37 seconds.
Not at all what I expected. Pretty much everyone was saying that ReiserFS was the way to go for many small files, and yet it was by far the slowest. Also, the effect of NFS vs. local was small.
I can see that the entire time I'm waiting for the page to return, imapd is pegging the CPU, so this might be CPU-bound. However, it could also be pegging the CPU simply because the CPU has nothing else to do and can dedicate 99.9% of its cycles to the imapd process. I would hope that one single imap session would not bring a Xeon 2.8GHz/1GB mem to its knees. Even still, I'll be able to compare in a couple of weeks when the 2nd processor and another 1GB of RAM comes in for these systems.
Now, I might just write this off and tell users "if you have folders with 27k messages in them, prepare for horrid performance", but it's just one of those things that you just want to make faster. :-)
Any and all ideas much appreciated! Given that I am seeing imapd tie up the entire time, I'm guessing this is probably not a SM problem - I realize that this mailing list is probably not the best place for this any more, but I wanted to followup and also, I'm sure some of you have seen similar stuff and might have good ideas. I will however be pinging the Courier IMAP list as well.
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
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