Hi,
>>> > I have a mail gateway system that consists of several
>>> > Postfix+MySQL+Amavisd-new machines behind a load balancer.
>>> >
>>> > I have defined a balancing policy based on number of SMTP sessions
>>> that
>>> > every server has to manage.
>>>
>>> New connections are given to the server with the fewest connections?
>>
>> Yes.
>>
>>> > But, even if the session is perfectly balanced, I see that the
>>> average
>>> > latency of a message in Postfix queues is too high on some machines
>>> and
>>> > quite zero on other.
>>>
>>> Are the same servers overloaded over a long period of time? And
>> lightly
>>> loaded servers remain lightly loaded?
>>
>> Usually.
>>
>>> What is the critical resource? Disk I/O? CPU? Output concurrency?
>>
>> Indeed, the number of sessions is correctly proportional to the weight I
>> have assigned to each server on balancer. But the load of the CPUs of
>> each machine not. I have watched Disk I/O with vmstat and OS never
>> swaps. I have a good quantity of RAM free.
>>
>> I monitored each machine's parameters using vmstat and what I could have
>> noted I is the number of blocked procs which is often nonzero (from 0 to
>> 3) when the mchine is overloaded.
>>
>> What do you mean for output concurrency?
>>
>> I have raised "maxproc" for amavis-filter to reduce the number of
>> blocked procs.
>>
>>> > What I infer is that every session can be used to devilver/send
>>> > different email messages (other then every message as inerently a
>>> > different size).
>>> >
>>> > It is right my argument or Im wrong in something? If yes, has
>> Postfix
>>> > the control of the number of message that could be manage by each
>>> SMTP
>>> > session?
>>>
>>> Take a look at "qshape", is there a lot of deferred mail on some
>>> systems
>>> and not others? Are you doing recipient validation, or accepting and
>>> bouncing a lot of mail?
>>
>> I constantly have monitored the Postfix queues with qshape, particularly
>> active queue:
>>
>> # watch "perl
>> /usr/local/src/postfix-2.5.2/auxiliary/qshape/qshape.pl -s active| head"
>>
>> I have a reasonably "normal" number of deferred emails (no more than 100
>> messages).
>>
>> Nevertheless, I'm doing recipient validation for each mailbox that I
>> manage and verification on each email of every domain for which I
>> forward messages.
>>
>> I fear that the problem is that for each session I can have an unsettled
>> number of messages sent over that session (It could be happen? If yes,
>> It could be depend on MTA settings?) other then an unsettled size of
>> SMTP traffic (which it determs the latency of messages and it could make
>> congestion of postfix active queue more or less heavy).
Could someone give me some hint about this issue?
TIA,
rocsca
