Hello, >> > 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).
Have someone further wideing to provide about this argument? rocsca
