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.)