[Dovecot] Internal Error form delivery from LDAP lookup.

[Jorgen Lundman]

Solaris-x86-10u8
Dovecot-1.2.7

Large mail setup, with quite a few MX servers working well. Generally everything 
is super.

But every now and then, we get "bouts of bad weather" - which only lasts a short 
time, and curiously nearly always occur when mail is sent to customer mailing 
lists. I suspect mostly because of that 1 message has multiple recipients within 
the same domain. Perhaps.

Delivery setup as:

main.cf:
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1
dovecot_destination_concurrency_limit=300

master.cf:
dovecot   unix  -       n       n       -       70       pipe
   flags=DRhu user=dovecot:dovecot argv=/usr/local/libexec/dovecot/deliver -f 
${sender} -d ${recipient}


Errors look something like:

example.com

Dec 06 08:46:25 deliver(rbc-005 at example.com): Info: 
msgid=<A22A602A940A45A49EA2C4CC53D27655 at UQC.local>: saved mail to INBOX

Dec 06 08:46:25 deliver(rbc-002 at example.com): Info: 
msgid=<A22A602A940A45A49EA2C4CC53D27655 at UQC.local>: saved mail to INBOX

Dec 06 08:46:28 deliver(rbc-004 at example.com): Error: userdb 
lookup(rbc-004 at example.com) failed: Internal failure

Dec 06 08:46:28 deliver(rbc-011 at example.com): Error: userdb 
lookup(rbc-011 at example.com) failed: Internal failure

Dec 06 08:46:28 deliver(rbc-013 at example.com): Error: userdb 
lookup(rbc-013 at example.com) failed: Internal failure

Dec 06 08:46:28 deliver(rbc-006 at example.com): Error: userdb 
lookup(rbc-006 at example.com) failed: Internal failure

Later on, when it retries, everything goes according to plan and delivery is 
achieved.


Now this is actually due to slapd saying:

Dec  6 08:46:25 vmx15.unix slapd[3958]: [ID 763815 local4.debug] 
connection_input: conn=72057 deferring operation: too many executing

And since it happens most frequently with mailing-lists, or mails with many 
recipients, I would guess it is due to a large number of lookups happening in a 
very short time.

Since dovecot_destination_recipient_limit=1, I believe 'deliver' is only ever 
called with just one recipient for "-d", and 'deliver' probably-does-not (?) 
query LDAP for any of the other "To:" addresses in the message body. Is that the 
case?

Secondary, the dovecot-ldap.conf for dovecot-auth has:

hosts = 127.0.0.1 172.20.12.33 172.20.12.23 172.20.12.113

So even though localhost's slapd was busy at the time, the other three hosts 
were definitely not. Is LDAP fail-over ... failing... in this case? How many 
concurrent queries does dovecot-auth perform? Any way to tweak this value?

Admittedly, postfix/dovecot does handle this situation correctly, as 'temporary 
failure' and mail delivery is merely delayed. But at the same time, it *could* 
be something with an easy fix as well.

Thoughts?

Lund

-- 
Jorgen Lundman       | <lundman at lundman.net>
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