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Re: Connection caching/SMTP piggybacking and postfix?

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  • Viktor Dukhovni
    ... One can t immediately re-use an existing connection when some other process is currently using it! To do that, one would have to always wait for the other
    Message 1 of 14 , Feb 28, 2013
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      On Thu, Feb 28, 2013 at 01:16:26PM +0100, Thorsten Glaser wrote:

      > > Connection caching has nothing to do with concurrency. Sheesh.
      >
      > I was assuming that, when you already have a connection to a
      > receiving MX, you'd not open another one but reuse the existing
      > one, so it would, of course, have something to do with that.
      >
      > If not? well, that's the qmail model.

      One can't immediately re-use an existing connection when some other
      process is currently using it! To do that, one would have to always
      wait for the other process to relinquish the connection, which forces
      concurrency <= 1. This has nothing to do with qmail, which uses a
      recipient limit of 1 which leads to more deliveries with multi-recipient
      messages than with Postfix or Sendmail.

      Postfix reuses *idle* existing connections, but creates new ones
      in *parallel* up to the concurrency limit to avoid severely limiting
      throughput to destinations with high capacity in the face of high
      single message delivery latency.

      Sendmail has no concurrency limits at all, since each process runs
      in isolation (no queue-manager), it just hiccups at random
      when the CPU load is high, which is not a meaningful signal that
      the MTA should pause deliveries or refuse new connections.

      You mentioned a Sendmail QueueLA or RefuseLA of 8, this is a meagerly
      limit on modern multi-cpu server hardware. ~10 years ago, I was
      tuning multi-CPU Sendmail servers of that era with a QueueLA of 64.

      > > I welcome you to propose a design that is as scalable as the rest
      >
      > I am *not* interested in Postfix. I'm not even primarily
      > working with Postfix.

      You're also not interested in any form of critical thinking before
      you spout non sequiturs, or even a modicum of humility which would
      suggest asking how to improve latency in your two MTA setup, nor do
      you care to do any research, rather you barge in here in response to
      an 11-year old post blaming Postfix for Sendmail design flaws.

      I smell a troll, please don't come back.

      --
      Viktor.
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