Queue Limit Policies
In order to limit the number of pending messages in Rendezvous queues, a transport property allows you to set a queue limit policy, as you would for TIBCO Rendezvous client applications.
When the queue limit for the transport is reached, the Rendezvous library discards a set number of messages. The default policy is TIBRVQUEUE_DISCARD_NONE, which means that no message is ever discarded. Setting TIBRVQUEUE_DISCARD_FIRST or TIBRVQUEUE_DISCARD_LAST allows you to specify the maximum number of Rendezvous messages that can be pending in the queue before the discard policy that you have selected is applied. When the limit is reached, the number of messages discarded is based on the discard amount value.
When the limit is reached, Rendezvous messages are discarded, and so are not imported as EMS messages, regardless of the EMS import delivery mode. As stated above, a Rendezvous message becomes a EMS message only after it has been dispatched from the Rendezvous queue. If a queue limit is exceeded, reliable Rendezvous messages are lost.
Rendezvous certified messages are not lost, but the message flow is interrupted. The redelivery of the missed messages is handled automatically by the Rendezvous libraries, and can not be controlled by the EMS server.
Reaching a queue limit also generates a Rendezvous advisory that is logged (see RVADV log and console trace in the TIBCO Rendezvous documentation), indicating which transport reached its queue limit. This advisory goes into an independent, non limited, Rendezvous queue. If lots of advisories are generated, this internal queue may also grow, signaling that the limit policy is not appropriate for your environment.
Take care when setting a queue limit policy. In a controlled environment where the risk of Rendezvous producers overwhelming the EMS server is low, there is no need to set a queue limit policy.