November 2019 - dovecot

warning: NFS hangs with dovecot 2.3.8 on Debian buster
by Jan-Pieter Cornet 01 Nov '19

01 Nov '19

A warning to those considering to upgrade to Debian 10 (buster): we have seen occasional NFS hangs with dovecot when using the stock debian buster kernel (4.19.67-2+deb10u1). When we downgrade to the debian stretch kernel (4.9.189-3+deb9u1), the issue does not occur. Note that we *only* downgraded the kernel, the rest of the OS is still debian buster. Dovecot 2.3.8. A little more info: we have a dovecot cluster, using mdbox for storage, on an NFS server (netapp Cmode version 9.6P2). We use a dovecot director layer, so a user is always connected to the same back-end dovecot server. The NFS hang occurs on the back-end server. Once the process hangs, other processes trying to write to the same mailbox, will get an error like this: Timeout (180s) while waiting for lock for transaction log file /var/mail/.../index/storage/dovecot.map.index.log (WRITE lock held by pid XXXX) The stuck process itself doesn't seem to do anything, is stuck in "D" disk state, "strace" doesn't show anything (and after attaching, strace itself needs a kill -KILL to stop). The only way to unwedge the process seems to be to do a kill -KILL of the stuck process. Reading from the mailbox is still possible. We are in the process of contacting the linux-nfs folks about this, but I'm trying to reproduce this on a test-cluster first, to be able to present a well-documented case. Since this hang doesn't happen immediately, but takes a few hours to a day to occur in the wild, or a few thousand writes to the same mailbox, it's a bit hard to debug. -- Jan-Pieter Cornet <johnpc(a)xs4all.net> Systeembeheer XS4ALL Internet bv www.xs4all.nl

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Dovecot and MySQL aborted connections.
by Benjamin Connelly 01 Nov '19

01 Nov '19

We also spotted these sql connections getting aborted, upon upgrading MySQL from 5.6 to 5.7. (Going back to 5.6 we don't see them!) Turning on mysql general query logging we can see it is Dovecot's mysql connections that inquire about or update quota usage in particular: *** /logs//mysql.log *** 2019-10-30T10:52:22.624690-07:00 2 Connect dovecot@localhost on npomail using Socket 2019-10-30T10:52:40.019780-07:00 2 Query SELECT bytes FROM quota2 WHERE username = 'a@bla' 2019-10-30T10:52:40.020948-07:00 2 Query SELECT messages FROM quota2 WHERE username = 'a@bla' 2019-10-30T10:53:40.113374-07:00 2 [Note] Aborted connection 2 to db: 'npomail' user: 'dovecot' host: 'localhost' (Got an error reading communication packets) Increasing mysqld's net_read_timeout and net_write_timeout values to 3600 does not stop the aborted connections. It seems asymptomatic. If the connection to mysql is still there to do quota operations, Dovecot seems to use it. If it's been aborted by the server, Dovecot seems to just (re)connect. . . But I'd love to help find the root or file a bug report or learn what it is we've configured wrong. . . Benjamin

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dovecot and ldap
by Maciej Milaszewski IQ PL 01 Nov '19

01 Nov '19

Hi Sorry for my question... I use dovecot+ldap How realy works (in dovecot-2.2.x ) lists of LDAP hosts to use ? ------ dovecot.conf ---- hosts = ldap.domain.pl:389 ldap-slave.domain.pl:389 #uris = -------- This is simpe HA ? I mean if ldap.domain.pl have problem another request go to ldap-slave.domain.pl ?

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