I just switched in a hurry one of our mailbox servers from UW-imapd to Dovecot in an attempt to address performance and stability problems.
This server hosts ~5500 accounts, ~2000 are daily used, ~600 simultaneous IMAP connexions in rush hours, and lots of POP ones. Some accounts may be accessed simultaneously with IMAP and POP.
The system is :
- Debian Sarge (x86 with amd64 kernel)
- MBOX files mailboxes
- indexes migrated out of filesystem quotas
- Sendmail MTA
- Procmail local delivery agent (not easily replaceable due to extensive use of procmailrc filters)
- Both Procmail and Dovecot use [dotlock, fcntl] as mailbox locking scheme
- No other processes have access to mailboxes in normal use
- Dovecot 1.0.8 hand-compiled from tarball
The good new is that it seems to perform better than UW-imapd.
The bad new is that we get lots or errors like this in log:
IMAP(username): FETCH for mailbox INBOX UID 23862 got too little data:3186 vs 3206
Such "accidents" happen about 4-5 times a day, and does not correct themselves, even with a mailbox expunge or reopen. However manual deletion of the faulty mailbox index seems to clear the problem, until another one occurs. On such errors some mail clients (Thunderbird) retry operation in infinite loop, so log gets really cluttered.
In imap-fetch-body.c it is stated : "We shouldn't really ever get here. One reason is if mail was deleted from NFS server while we were reading it. Another is some temporary disk error."
Both reasons do not seem to apply in our case: mail partition is not NFS-mounted, and disks (a RAID5 array) seem healthy. Furthermore, affected accounts are not over quota.
So may we have found a bug ? Or may we have a locking problem ? Or an index handling one ?
I tried to disable mbox_lazy_writes without success. I will try to disable disk indexes totally, which should help since problems seem index-related; but performance may suffer.
Any clues appreciated...
Dovecot -n says :
# 1.0.8: /usr/local/etc/dovecot.conf protocols: imap imaps pop3 pop3s listen: [::] ssl_cert_file: /usr/local/etc/ssl/private/our-certificate.pem ssl_key_file: /usr/local/etc/ssl/private/our-certificate.pem disable_plaintext_auth: no login_dir: /var/run/dovecot/login login_executable(default): /usr/local/libexec/dovecot/imap-login login_executable(imap): /usr/local/libexec/dovecot/imap-login login_executable(pop3): /usr/local/libexec/dovecot/pop3-login first_valid_uid: 200 first_valid_gid: 200 mail_location: mbox:~/mail:INBOX=~/mail/INBOX:INDEX=/espace/dovecot/indexes/%u fsync_disable: yes mbox_lazy_writes: no mail_executable(default): /usr/local/libexec/dovecot/imap mail_executable(imap): /usr/local/libexec/dovecot/imap mail_executable(pop3): /usr/local/libexec/dovecot/pop3 mail_plugins(default): quota imap_quota mail_plugins(imap): quota imap_quota mail_plugins(pop3): quota mail_plugin_dir(default): /usr/local/lib/dovecot/imap mail_plugin_dir(imap): /usr/local/lib/dovecot/imap mail_plugin_dir(pop3): /usr/local/lib/dovecot/pop3 imap_client_workarounds(default): outlook-idle tb-extra-mailbox-sep delay-newmail imap_client_workarounds(imap): outlook-idle tb-extra-mailbox-sep delay-newmail imap_client_workarounds(pop3): outlook-idle pop3_uidl_format(default): pop3_uidl_format(imap): pop3_uidl_format(pop3): %08Xv%08Xu pop3_client_workarounds(default): pop3_client_workarounds(imap): pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh auth default: passdb: driver: pam args: * userdb: driver: passwd plugin: quota: fs
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