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From <Alexander.Fitt...@gdata.de>
Subject Server-side flow control crashes python client (qpid-0.28)
Date Tue, 01 Jul 2014 16:08:59 GMT
Hello everyone! 

I'm currently stuck with a problem while using flow control on the Java broker and a python
client. 

Info about the setup: 
Ubuntu Server 14.04 LTS 
Java Broker and Python client library are the most current stable version 0..28, the broker
is running with a default configuration using a derbystore persistence layer. The queue in
question is both durable and permanent. The sent messages are _not_ marked as durable. 

We are running into severe problems because the QPID server crashes under heavy load when
some of the consumers fail to drain their respective queues. This fills up the available heap
space and eventually leads to an OutOfMemory Exception which crashes the Java Broker. I suppose
that messages which are not explicitly marked as durable will never be written to the permanent
storage, even though the heap space is full and there is no explicit consumer throttling,
so this would be the expected result. Is this assumption correct? 

To avoid this condition I've set up a queue with a Flow Control Threshold of 100MB and a Flow
Resume Threshold of 80MB on the Broker (Low values for testing). While filling up the queue
with some random messages, as soon as it hits the size limit, the python client crashes with
an exception that doesn't seem to be the intended reaction in this case: 

Traceback (most recent call last):
  File "qpid_test_flow.py", line 104, in <module>
    sys.exit(main())
  File "qpid_test_flow.py", line 86, in main
    produce_messages()
  File "qpid_test_flow.py", line 59, in produce_messages
    qpid_sender.send(msg)
  File "<string>", line 6, in send
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 889, in
send
    self.sync(timeout=timeout)
  File "<string>", line 6, in sync
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 901, in
sync
    if not self._ewait(lambda: self.acked >= mno, timeout=timeout):
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 814, in
_ewait
    result = self.session._ewait(lambda: self.error or predicate(), timeout)
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 580, in
_ewait
    result = self.connection._ewait(lambda: self.error or predicate(), timeout)
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 219, in
_ewait
    self.check_error()
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/endpoints.py", line 212, in
check_error
    raise e
qpid.messaging.exceptions.InternalError: Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/qpid/messaging/driver.py", line 669, in write
    op.dispatch(self)
  File "/usr/local/lib/python2.7/dist-packages/qpid/ops.py", line 84, in dispatch
    getattr(target, handler)(self, *args)
AttributeError: Engine instance has no attribute 'do_message_set_flow_mode'

The official documentation is rather quiet about client-side handling of server-side enforced
Flow Control Limits. In the source code, there is a TargetCapacityExceeded Exception, which
is a subclass of SenderError, so this would be the expected Exception when the capacity limit
is reached. 


As a temporary workaround, If I catch the InternalError, set the 'error' Attribute of the
qpid connection to None and wait for a short time, I can loop over the sender until the queue
reaches the Flow Resume Threshold. But  I'm afraid that this is not the intended way of handling
this, as the Traceback suggests that the Python client is unable to handle some unknown server
request. 

Can somebody help me out here? 


Kind regards, 

Alex. 
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