> > 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).
rocsca
