On 09/21/2010 01:06 AM, Stan Hoeppner wrote:
Victor Duchovni put forth on 9/20/2010 6:01 PM:
On Tue, Sep 21, 2010 at 12:56:14AM +0200, Jeroen Geilman wrote:
Yes, when traffic to the destination is light (message deliveries
are spaced multiple seconds or more apart) or is very heavy (message
deliveries are many in each interval equal to the delivery of a single
message). When traffic is moderate, demand connection caching may
introduce some short-term bias towards recently used IPs. As the load
rises multiple connections are cached in parallel, and these will tend
to use all the available IPs.
Am I correct in thinking that this adaptive behaviour is designed to
prevent overloading the nameservers postfix talks to ?
No, not at all, DNS lookups are cached and therefore cheap. It is
SMTP connection setup that is expensive for heavily loaded destinations
with multiple MX hosts behind load-balancers, where some MX hosts may
be slow to respond and initial connections are subjected to various DNS
tests, ... that don't apply to a second message for the same connection.
Connection caching is especially attractive when some MX hosts are
down and non-responsive, incurring high connection setup latency.
Maybe worth reading the relevant documentation on connection caching:
http://www.postfix.org/scache.8.html
Thanks Victor and Stan, will definitely read that.
--
J.
