On Tue, Jul 06, 2010 at 11:21:19AM -0700, Florin Andrei wrote:
> On 06/30/2010 11:17 AM, Wietse Venema wrote:
>> When sending mail via SMTP, Postfix randomizes the order of
>> equal-preference server IP addresses.
>>
>> However, with SMTP connection caching enabled, the faster SMTP
>> server will get more mail than the slower SMTP server.
>
> It seems you imply that disabling the connection cache will equalize the
> distribution. Or is it not that simple?
No, disabling the cache will still leave a skewed distribution. Connection
creation is uniform across the servers, but connection lifetime is much
longer on the slow server, so its connection concurrency is much higher
(potentially equal to the destination concurrency limit under suitable
conditions, thus keeping the fast servers essentially idle).
A time-based cache is the fairness mechanism that keeps connection
lifetimes uniform across the servers, which ensures non-starvation
of fast servers, and avoids futher overload of (congested) slow servers.
> Note: The systems are pretty fast and the connections are not slow either -
> one is local, the other is over a reasonably fast data link.
The <usual stuff> is not always hitting the fan, otherwise the fan would
be off. :-)
--
Viktor.
