[Mailman-Developers] load balancing with mailman.

[Marc MERLIN]

On Tue, Jan 29, 2002 at 02:40:56PM -0500, Barry A. Warsaw wrote:
>     MM> Barry: With the new qrunner infrastructure, does qrunner still
>     MM> need to lock the lists during delivery?  If qrunner doesn't
>     MM> modify config.db anymore, could it open config.db read only?
> 
> Remember that now, we have usually 7 queues, and each one has its own

Yep.

> runner process.  One of the advantages of this is that we can really
> isolate lock acquisition to a finer granularity.  In fact,
> OutgoingRunner -- which processes qfiles/out files, and thus is the
> process that actually calls SMTPDirect -- does not lock the lists for
> the normal delivery processing.  It simply shovels messages from the
> queue to smtpd and doesn't need to update any list information, as
> that's all done before the message gets to the outgoing queue.

Awesome, just what I was hoping for.

> There's one exception (of course ;).  If your smtpd ever returns
> synchronous errors, then Mailman has to lock the list in order to
> register bounces.  However, Mailman only does this periodically, and
> this is controllable by the variable DEAL_WITH_PERMFAILURES_EVERY in
> Mailman/Queue/OutgoingRunner.py (it's not a mm_cfg.py variable).

That's not a real problem. Even if there is a race condition somewhere, this
case should be sufficiently rare for the race not to happen.

> By default this is set to 1, but you could crank it up so that the
> culling of the known bounces is done less frequently.  OTOH, if your

Good to know.

> MTA is set up to never do recipient tests/deliveries synchonously (and
> you're not delivering to local users), you should never have such
> delivery failures to deal with, thus you'd never need to lock the
> list.

Thanks  a bunch. 
This should definitely  allow for load sharing and  some failover capability
(the second server periodically rsyncs the NFS exported mailman tree in case
the  first list  server,  which exports  ~mailman minus  qfiles  which is  a
symlink to local disk, dies.
So, if this happens, you can move a symlink and continue with one server and
an rsynced copy of the whole tree that is hopefully not too old)

Marc
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