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From "Stirling Chow (JIRA)" <j...@apache.org>
Subject [jira] [Created] (AMQ-3331) When a producer from a network bridge is blocked by producer flow control, all producers from the network bridge get blocked.
Date Thu, 19 May 2011 17:24:47 GMT
When a producer from a network bridge is blocked by producer flow control, all producers from
the network bridge get blocked.
-----------------------------------------------------------------------------------------------------------------------------

                 Key: AMQ-3331
                 URL: https://issues.apache.org/jira/browse/AMQ-3331
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker, Test Cases, Transport
    Affects Versions: 5.5.0
            Reporter: Stirling Chow


Symptom
=======
Broker A produces messages to two queues, Q1 and Q2.  Broker B consumes messages from two
queues, Q1 and Q2.  Broker A is connected by a demand forwarding bridge, over TCP, to Broker
B so that messages produced to Q1/Q2 will be forwarded to the consumers on Broker B.

At some point, Broker B's instance of Q2 becomes full (e.g., because the Q2 consumer is slow),
and this triggers producer flow control to halt new messages being sent to Broker B's Q2 over
the bridge.  Broker A's instances of Q1/Q2 are not full, so the producers on Broker A are
not blocked.

If the messages produced by Broker A are *persistent*, we see this behaviour over the course
of the production of 1000 messages to both Q1/Q2, where Broker B's Q2 becomes full on the
500th message:

Broker A       Bridge        Broker B
========                     ========
0->1000->0     ------>       0->1000->...
0->1000->500                 0->500->...

The above results, which assume network and consumer prefetch sizes of 1, are what we expected,
namely: 
  1) Broker A produces 1000 messages to Q1 without blocking and all of these messages are
forwarded to Broker B's Q1 without blocking, eventually being consumed by Broker B's Q1 consumer.
  2) Broker A produces 1000 messages to Q2 without blocking and 500 of these messages are
forwarded to Broker B's Q2 before producer flow control blocks the flow until Broker B's Q2
consumer can start reducing the queue size.

This is good because the bridge treats Q1 and Q2 independently (i.e., producer flow control
on Q2 does not block the messages forwarded to Q1).

If the messages produced by Broker A are *non-persistent*, we see this behaviour:

Broker A       Bridge        Broker B
========                     ========
0->1000->500   ------>       0->500->...
0->1000->500                 0->500->...

The above results, which assume network and consumer prefetch sizes of 1, are not what we
expected, namely: producer flow control on Broker B's instance of Q2 blocks the forwarding
of messages to Broker B's instance of Q1.

This is not good because producer flow control on Q2 essentially triggers producer flow control
on Q1, even though Q1 is *not* full.

It also seems strange (and almost non-intuitive until you understand the cause), that peristent
messages should behave better than non-persistent messages.  The same difference in behaviour
can also be observed with persistent messages if Broker A these outside a JMS transaction
(e.g., AUTO_ACKNOWLEDGE) versus inside a JMS transaction: outside behaves appropriately, with
Q1 independent of Q2, but inside behaves the same as the non-persistent case with Q1 blocked
by Q2.

These observations are contrary to the AMQ 5.0 documentation regarding producer flow control:
{quote}As of ActiveMQ 5.0, we can now individually flow control each producer on a shared
connection without having to suspend the entire connection.{quote}

Cause
=====

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