Hello, I am new to the list and have spent extensive time researching performance suggestions through the list and the documentation. Particularly interesting is the recent performance thread related to the upcoming release.
I just upgraded one of our email servers from tpop3d to dovecot 1.0rc19. tpop3d has served us well for many years; however, it basically has lost all it's support and developers. My main liking of tpop3d was it's speed. After the upgrade to dovecot, the server began to crawl. This server runs postfix for the delivery agent and now dovecot for pop3 and imap. The box serves roughly 9000 virtual maildir mailboxes with roughly 20 pop3 processes active at any given time.
I ran some tests this morning to determine an exact difference between running tpop3d and dovecot. dovecot: I/O load averages 81%, System load averages 12.00 tpop3d: I/O load averages 20%, System load averages 0.50
To ensure it wasn't just a fluke of logins, I let each app run for several minutes, and did the test multiple times. The results were not any abnormal user usage and definitely related to application performance.
My current settings in dovecot related to performance are: mmap_diable = yes mmap_no_write = yes Modifying these to no seems to decrease performance slightly but only a few percent.
I have also played with various other settings, which didn't give me any significant performance boost.
I'm eager for the next release which will have the fsync_disable option to see if that helps, it certainly looks promising.
One observation where the majority of the load seems to be generated from is when a pop3 connection is loading up a very large maildir. The pop3 process seems to remain around using I/O for a considerable time, even when the user has no new email. Perhaps it is rebuilding or verifying it's index files? Here is an example of a lsof of the pop3 process with a user who has roughly 17000 messages. They check their email every 10 minutes which seems to add significant load. Note the final line, it's reading an individual message file, yet the user has no new email since the last login. If i keep lsofing the process, the final file seems to change and keep going through many of their mailbox files. The process takes many minutes to complete. Is it rebuilding the index on every login?
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME pop3 15148 postfix cwd DIR 9,2 152 850160 /home/domain.net/brock pop3 15148 postfix rtd DIR 9,2 816 2 / pop3 15148 postfix txt REG 9,2 1888690 7096106 /usr/local/libexec/dovecot/pop3 pop3 15148 postfix mem REG 9,2 107724 182934 /lib/ld-2.3.2.so pop3 15148 postfix mem REG 9,2 1578228 182936 /lib/tls/libc-2.3.2.so pop3 15148 postfix mem REG 9,2 16312 88977 /lib/libdl-2.3.2.so pop3 15148 postfix 0u IPv4 873280915 TCP domain.net:pop3->dsl.dyn.06-99.uslogin.net:40950 (CLOSE_WAIT) pop3 15148 postfix 1u IPv4 873280915 TCP domain.net:pop3->dsl.dyn.06-99.uslogin.net:40950 (CLOSE_WAIT) pop3 15148 postfix 2w FIFO 0,5 873280916 pipe pop3 15148 postfix 3r CHR 1,9 27963 /dev/urandom pop3 15148 postfix 4r FIFO 0,5 873281456 pipe pop3 15148 postfix 5w FIFO 0,5 873281456 pipe pop3 15148 postfix 6r FIFO 0,5 873281457 pipe pop3 15148 postfix 7w FIFO 0,5 873281457 pipe pop3 15148 postfix 8u REG 9,2 205740 7272682 /var/spool/mail/domain.net/brock/dovecot.index pop3 15148 postfix 9u REG 9,2 15020 7225137 /var/spool/mail/domain.net/brock/dovecot.index.log pop3 15148 postfix 10u REG 9,2 1585152 7290906 /var/spool/mail/domain.net/brock/dovecot.index.cache pop3 15148 postfix 11r REG 9,2 1992 5040734 /var/spool/mail/domain.net/brock/cur/1165164651.V902I4cea5e.s3.visp.net:2,S
I'm eager to solve this new I/O issue which has cropped up after upgrading to dovecot. Despite the severe performance degradation, I feel dovecot has awesome potential and is feature rich, and most importantly it's being maintained, so I want to stick with it!
Thank you for any help offered! I'm hopeful for any suggestions to solve this performance issue or diagnose it further to determine the cause.
- Nate