:
:On Wed, Jun 20, 2001 at 12:04:22AM -0700, Matt Dillon wrote:
:>
:> A web proxy could be
:> round-robined fairly easily, but for a mail relay it is often a good
:> idea to split the incoming and outgoing mail into two separate round
:> robins (two separate groups of machines).
:
:Why's that? So you can tune each type of machine appropriately for
:the task? How would you tune incoming and outgoing mail servers
:differently?
:
:--
: Ben
That's the idea. A mail relay would be tuned for its purpose. The
queueing characteristics for relaying to internal hosts are going to be
very, very different then the queueing characteristics for relaying
to extern (internet) hosts. So different that by separating the
functionality you can squeeze out considerably more performance out
of each machine and, as a bonus, make the overall system more reliable.
Now if you get a deluge of mail in one particular direction, it will not
effect mail going in the other direction at all.
So instead of having 6 generic mail relay boxes in a round robin you
might instead have 4 boxes to relay outgoing mail to the internet
and 2 to relay incoming mail to internal machines, with the outgoing
boxes tuned to handle huge queues and the incoming machines tuned to
handle lots of incoming connections but smaller queues (relaying to
internal hosts being much faster, less prone to hicups, and the
queue-runner's persistent connection caches being much easier to
maintain).
-Matt
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