hector <gmail(_dot_)sant9442(_at_)winserver(_dot_)com> wrote:
Tony Finch wrote:
Exim has a database of which messages are waiting for which hosts, so when a
host comes back to life it can flush the messages down the same connection
without having to wait for the next queue run.
Is that batched (collection pointer, perhaps) before the connection is made or
is this part of "Online Hold" and EXIM does a database check for any more mail
for the current target host?
The latter, I think, depending on what you mean by "online hold". When a
message arrives, Exim normally tries to deliver it immediately. If that
succeeds it looks at the "waiting" hints database to see if there are any
messages queued for the same host, and delivers them immediately. There
is no in-memory state for these queued messages. Exim doesn't keep SMTP
connections idle, and normally runs the queue in a random order.
But if each Ms is transferred concurrently, then the total throughput time is
no higher then the maximum Ts transaction. This begins to less true as the
total concurrency increases to a threshold where scaling and bottlenecking
issues come into play.
Yes. Exim has an option to serialize deliveries to certain hosts, in which
case there is another hints database recording currently active
connections. When Exim is about to connect to a host it checks this
database and skips the host if there is a record for it. If there aren't
any other destination hosts the message will be queued and should soon be
picked up by the waiting mechanism. (This is more likely if the target is
relatively slow, which is what the feature was designed for.) We use this
to avoid load spikes caused by large mailing list deliveries to our
message store servers, but not for general purpose deliveries.
Tony.
--
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