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295433Re: Connection Speed

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  • Roman Gelfand
    Sep 12, 2013
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      you are right. The telnet connection from that machine was instantaneous.

      On Thu, Sep 12, 2013 at 10:14 AM, Viktor Dukhovni
      <postfix-users@...> wrote:
      > On Thu, Sep 12, 2013 at 10:03:58AM -0400, Roman Gelfand wrote:
      >
      >> Based on comments made by Wietse, it looks like my server is in good
      >> shape as the connections are not even taking a second and the whole
      >> process is taking roughly a second.
      >
      > Whether that is slow or not depends on what throughput (messages
      > sent per second) you're trying to achieve and what concurrency
      > (number of parallel submission processes or threads) you're using
      > to submit mail. Mail delivery is "congested" when the output rate
      > is below the input rate, otherwise mail is inevitably delayed in
      > transit by a short time, but that is rarely a concern.
      >
      >> Based on what Viktor is saying, this line could be a problem
      >>
      >> Sep 12 09:39:56 pmx1 postfix/smtpd[30058]: connect from unknown[192.168.0.86]
      >>
      >> as it could to take some to time to attempt resolve this dns. Is this
      >> correct?
      >
      > A single log message with a single timestamp in isolation is NOT
      > evidence of delay. All we see is that reverse resolution of
      > [192.168.0.86] failed, whether this took any appreciable time is
      > not evident from this log entry alone. There are often prior log
      > entries warning about the resolution failure of DNS lookups timed
      > out, ...
      >
      > To determine whether there is a delay, use "telnet" to connect from
      > 192.168.0.86 to port 25 on the MTA, and see how long you have to wait
      > until the MTA responds with a "220 ..." banner.
      >
      > You can also capture with "tcpdump" and see timestamps to the
      > microsecond showing how long it takes from TCP SYN to "220 ..."
      > (and what DNS lookups are taking time in between).
      >
      > --
      > Viktor.
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