February 2006 - dovecot

Re: [Dovecot] Question about Dovecot and NFS
by Tony Kay 02 Feb '06

02 Feb '06

On Wed, 01 Feb 2006 11:45:16 +0200, Timo Sirainen <tss(a)iki.fi> wrote: > On Tue, 2006-01-31 at 22:42 -0800, Tony Kay wrote: > > How does dovecot handle this kind of conflict. I.e. how would one dovecot IMAP on server A detect that dovecot on server B had rewritten something like flags on the mailbox they are both accessing? I'm sure it doesn't leave the dot lock sitting around, since that would block mail delivery. > > It just checks if mbox's mtime has changed. If it has, it checks if > there are new mails or if it needs to do some other synchronization > (mbox_dirty_syncs / mbox_very_dirty_syncs causes it to delay it as long > as possible). > > UW-IMAP also checks if mtime has changed, but instead of trying to > figure out what changed it just disconnects the client with an > "unexpected mbox change" error. UW uses a "kiss of death" signal for collaborative locking...the mtime changes are all assumed to be appends as far as I know. The problem (which I can reproduce) comes with a situation like this: - IMAP host A and B access INBOX for the same user from different physical servers which share the inbox via NFS - Neither sees the other (because UW imap assumes lingering opens come from c-client apps, and it uses signals/flock/tmp to sync them, which are not available when A and B are on separate hosts). - Delete and expunge a message on B - 'A' can still read the expunged message. - Mark two messages for delete on A, including the one previously expunged by B - New message delivered to inbox (possibly by yet another host) - Expunge on A - New message is lost My theory is that the two IMAPs are both holding a fd open, and this causes one of the copies to become stale (in the sense it no longer has a filesystem name). The new mail is delivered to the non-stale box, and then the expunge on 'A' causes the stale open file to be "rewritten" over the top of the non-stale one. Result: mail loss. We also see things like message flags that magically reset themselves, etc. I did some testing w/dovecot 0.99 earlier in this same config, and it seems like it has some issues. For example a delete/expunge on IMAP A was "sort-of" seen by the B (fetch complained that the UIDs had changed, and would not work until a NOOP was done...this is technically OK), but B magically restored the deleted message with a new UID (which is not so good, since a client that caches stuff may now have a strange view of the world...I need to examine the set of "update" notices that went along with these events to better understand the implications). This also worries me because the "magic" reappearance indicates a copy from a stale fd, which could exhibit the same mail loss I produced w/UW IMAP. I am planning on updating to your latest source tree tomorrow (I am out of time today), and see if I can make it "lose" new mail. Opinions??? Thanks! Tony

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[Dovecot] Can't send mail through new server
by Anne Wilson 02 Feb '06

02 Feb '06

I thought I had just about got the old server to the point of being switched off. I have been reading from the dovecot server for a couple of days, and this evening I switched the 'sending' to the new server as well - but I couldn't get anything out. I got: Error while uploading message Could not upload the message dated Wed Feb 1 21:2:56 2006 from Anne Wilson <cannewilson(a)tiscali.co.uk> with subject "xxx" on the server. The destination folder was sent-mail, which has the URL . The error message from the server communication is here: APPEND failed: Can't open append mailbox : Read-only file system ---------- I also got messages like: Error while retrieving messages from the server. Unable to open folder sent-mail. The server replied: SELECT failed: Mailbox open failed, aborted: Read-only file system. --------------- I like to save the sent-mail and trash on the server. ~/Maildir has all the folders including sent-mail and trash. I have the same UID on both boxes. What has gone wrong? Anne -- Registered Linux User No.293302 (http://counter.li.org/)

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[Dovecot] Can't send mail from new server
by Anne Wilson 01 Feb '06

01 Feb '06

I thought I had just about got the old server to the point of being switched off. I have been reading from the dovecot server for a couple of days, and this evening I switched the 'sending' to the new server as well - but I couldn't get anything out. I got: Error while uploading message Could not upload the message dated Wed Feb 1 21:2:56 2006 from Anne Wilson <cannewilson(a)tiscali.co.uk> with subject "xxx" on the server. The destination folder was sent-mail, which has the URL . The error message from the server communication is here: APPEND failed: Can't open append mailbox : Read-only file system ---------- I also got messages like: Error while retrieving messages from the server. Unable to open folder sent-mail. The server replied: SELECT failed: Mailbox open failed, aborted: Read-only file system. --------------- I like to save the sent-mail and trash on the server. ~/Maildir has all the folders including sent-mail and trash. I have the same UID on both boxes. What has gone wrong? Anne -- Registered Linux User No.293302 (http://counter.li.org/)

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[Dovecot] Can't send from the new server
by Anne Wilson 01 Feb '06

01 Feb '06

I thought I had just about got the old server to the point of being switched off. I have been reading from the dovecot server for a couple of days, and this evening I switched the 'sending' to the new server as well - but I couldn't get anything out. I got: Error while uploading message Could not upload the message dated Wed Feb 1 21:2:56 2006 from Anne Wilson <cannewilson(a)tiscali.co.uk> with subject "xxx" on the server. The destination folder was sent-mail, which has the URL . The error message from the server communication is here: APPEND failed: Can't open append mailbox : Read-only file system ---------- I also got messages like: Error while retrieving messages from the server. Unable to open folder sent-mail. The server replied: SELECT failed: Mailbox open failed, aborted: Read-only file system. --------------- I like to save the sent-mail and trash on the server. ~/Maildir has all the folders including sent-mail and trash. I have the same UID on both boxes. What has gone wrong? Anne -- Registered Linux User No.293302 (http://counter.li.org/)

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[Dovecot] extremely slow delete/move operations?
by Gregory K. Ruiz-Ade 01 Feb '06

01 Feb '06

I've been working to migrate several hundered users on to our new mail servers, which run dovecot 0.99.11 (RHEL4). The problem I'm seeing is that deleting or moving a message seems to take a very long time. It's not uncommon for Thundirbird (1.0.7) to have delays of 5-10 seconds to delete a single message from my Inbox (<500k) and place it in my Trash folder (~100MB right now). The systems are Dell PowerEdge 1850 (dual 3.6GHz Xeon) with two 300GB SCSI drives in a hardware mirror. Filesystems are ext3 on LVM. Inboxes are on /var/spool/mail (/export/mail, symlinked into /var). User mail folders are in their home directories (/export/homes1/<user>, automounted to /home/<user>; some home directories are NFS automounted from a NetApp). Both the mail spool and home directories are available over NFS for compatibility reasons with the former setup. What's really bugging me is that I've used the same software (RHEL4 and dovecot 0.9x.x) at my last workplace, and the performance was outstanding; it beat UWIMAPd hands-down, especially with large mailboxes. Here, the opposite seems to be true. The primary difference seems to be that we're using NFS here, but I wasn't using NFS at my last job. I'm getting a lot of grief over the delays when users delete mail or move mail from their inbox to one of their mail folders. Enough so that they're now resisting moving to the new server. Where do I look to find out what's causing the slowness? What can I do to make it faster? Mailbox formats are mbox. Using these options in /etc/dovecot.conf: ----- protocols = imaps pop3s imap_listen = [::] pop3_listen = [::] ssl_cert_file = /usr/share/ssl/certs/csefast.ucsd.edu_cert.pem ssl_key_file = /usr/share/ssl/private/csefast.ucsd.edu_key.pem login_dir = /var/run/dovecot-login login = imap login = pop3 verbose_proctitle = yes first_valid_uid = 100 default_mail_env = mbox:~/:INBOX=/var/mail/%u mail_full_filesystem_access = yes mbox_locks = dotlock fcntl auth = default auth_mechanisms = plain auth_userdb = passwd auth_passdb = pam auth_user = root ----- Thanks in advance, Gregory -- Gregory K. Ruiz-Ade Sr. Systems Administrator Computer Science and Engineering University of California, San Diego Office: EBU3b 1216 Phone: (858) 822-2625 E-mail: gkra(a)ucsd.edu

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Re: [Dovecot] Question about Dovecot and NFS
by Timo Sirainen 01 Feb '06

01 Feb '06

On Tue, 2006-01-31 at 22:42 -0800, Tony Kay wrote: > How does dovecot handle this kind of conflict. I.e. how would one dovecot IMAP on server A detect that dovecot on server B had rewritten something like flags on the mailbox they are both accessing? I'm sure it doesn't leave the dot lock sitting around, since that would block mail delivery. It just checks if mbox's mtime has changed. If it has, it checks if there are new mails or if it needs to do some other synchronization (mbox_dirty_syncs / mbox_very_dirty_syncs causes it to delay it as long as possible). UW-IMAP also checks if mtime has changed, but instead of trying to figure out what changed it just disconnects the client with an "unexpected mbox change" error.

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