This example is taken from a Feb 2004 discussion on the Postfix
Users list. Congestion was reported with the active and incoming
queues large and not shrinking despite very large delivery agent
process limits. The thread is archived at:
https://groups.google.com/groups?th=636626c645f5bbde
Using an older version of
qshape(1) it was quickly determined
that all the messages were for just a few destinations:
$ qshape (show
incoming and
active queue status)
T A 5 10 20 40 80 160 320 320+
TOTAL 11775 9996 0 0 1 1 42 94 221 1420
user.sourceforge.net 7678 7678 0 0 0 0 0 0 0 0
lists.sourceforge.net 2313 2313 0 0 0 0 0 0 0 0
gzd.gotdns.com 102 0 0 0 0 0 0 0 2 100
The "A" column showed the count of messages in the
active queue,
and the numbered columns showed totals for the
deferred queue. At
10000 messages (Postfix 1.x
active queue size limit) the active
queue is full. The incoming was growing rapidly.
With the trouble destinations clearly identified, the administrator
quickly found and fixed the problem. It is substantially harder to
glean the same information from the logs. While a careful reading
of
mailq(1) output should yield similar results, it is much harder
to gauge the magnitude of the problem by looking at the queue
one message at a time.
