Explanation: When a message flow opens a WebSphere MQ queue,
for example in the MQInput or MQOutput node, the queue is held open until
the message flow is redeployed or removed from the execution group, or until
the broker is stopped. In Version 2.1,
the execution group queue cache is shared between threads in the message flow,
even though queue handles are unique to a thread. When the number of queue
handles reaches a threshold, older queue handles are considered for closing.
The default threshold in Version 2.1 is 30. In Version 6.0, each thread maintains its own queue
cache, and the new default threshold per thread is 240. Therefore an execution
group maintains far more open queue handles than in the previous version,
particularly if it has started a large number of threads. (The same behavior
is also true for Version
5.0, therefore message
flows migrated from Version
5.0 are unaffected
in this way when you migrate them.)