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From mARK bLOORE <mblo...@gmail.com>
Subject all subscribers not equal?
Date Wed, 27 Jan 2010 19:12:55 GMT
I am using the java broker 0.5 and the python client.  I have a queue
with one publisher and (usually) three subscribers.
The publisher sends messages at a fairly constant rate.
The subscribers take messages in a single thread at an unlimited rate,
put them in a buffer, and ack the messages immediately.  If the buffer
fills then they block before the ack.

Normally all the subscribers get messages at about the same rate, and
the queue's message count is mostly zero.  If a subscriber starts to
block then the message count may rise, and when it gets to the tens of
thousands I reduce the publication rate.  But an odd situation
appears:  The blocked subscriber takes messages into its buffer as
fast as it takes them out, but the other two subscribers get messages
at only one third of the rate that the publisher is adding them.  That
first subscriber is running many times faster.

If I add a fourth subscriber it gets messages at one quarter the
publication rate, and the other two start getting messages at that
rate too.  If I kill the fourth subscriber rates return to what they
were.

If I kill the first subscriber then the other two start taking
messages very fast, and the backlog in the queue quickly disappears.

It seems as if the broker has earmarked the backlogged messages for
that one subscriber, and won't deliver them to any other unless that
one goes away.  Could that be the case?  Note that a subscriber may
have at most one unacked message.

I'm afraid I can't abstract any reasonable amount of code to display.
I'm not sure that would help anyway.

-- 
mARK bLOORE <mbloore@gmail.com>

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