How SYSTEM.INTER.QMGR.PUBS queue works with Local & Cluster Topics

Question

I am seeing an issue in MQ cluster infrastructure where messages pile up in SYSTEM.INTER.QMGR.PUBS which is present in a queue manager with
cluster topics defined.
Infocenter says "In a publish/subscribe cluster, those publications are targeted at the SYSTEM.INTER.QMGR.PUBS queue on the remote queue
managers that host the subscriptions."

I would like to know how the message flow works with SYSTEM.INTER.QMGR. PUBS queue in a queue manager with Topics & subscriptions defined as

1. Cluster Topics & local susbcriptions
2. Local Topics & local subscriptions

Can anyone help here to understand whether messages flow through SYSTEM.INTER.QMGR.PUBS queue if Topics are defined local to a queue manager?

Answer 1

I would expect messages flow through the SYSTEM.INTER.QMGR.PUBS queue of a queue manager when the queue manager has local subscriptions to a topic, which is published to by publishers connected to a remote queue manager, or when the queue manager is a topic host in a cluster using topic host routing, or when the queue manager is member of a publish/subscribe hierarchy.

It doesn't matter whether the topic object is defined remotely or locally, messages will flow through this queue when the queue manager is on the route between remote publishers and subscribers.

http://www.ibm.com/support/knowledgecenter/SSFKSJ_8.0.0/com.ibm.mq.mon.doc/q005262_.htm%23q005262_?lang=en

Answer 2

The SYSTEM.INTER.QMGR.PUBS is made use if the Topics are defined in cluster and there are no local defined queue objects in the same queue manager for remote publishers(queues) to publish messages to cluster Topics.In this case all published messages pass through this queue to reach Topics.

But if the Topics are defined as local Topics are there are alias queue objects defined in the same queue manager which are mapped to Topics; then all remote publishers(queues) will publish to the alias queues defined and skip the SYSTEM.INTER.QMGR.PUBS. In this case this queue is not made use for publishing.