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We have a queue manager in Production system which is having around 10 cluster topics and 50 subscriptions. All the queue managers are in IBM MQ cluster topology and the data in NAS ( shared storage ) so that all queue managers are MI ( Multi-instance) enabled. We have huge volume message flow for publish-subscribe. But we sometimes see messages just get piled up in SYSTEM.INTER.QMGR.PUBS in the queue manager where Topics & subscriptions are defined and to get the message flow back again we will have to restart the queue manager. I am trying to understand what are the possible scenarios we could get this issue. I have read few of them like if there is no consumers on the destination subscription queue messages might get piled up in this SYSTEM queue. But in our case all the cluster transmit & other subscription queues are empty when we see this backlog. Any help or anyone seen similar behaviour??

JoshMc
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sijo0703
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2 Answers2

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As Shashi says, this queue is where inbound publications arrive from other queue managers in the MQ cluster. It is the queue manager's responsibility to process these messages as quickly as possible and send them on to any matching subscriptions. The behaviour of the consuming subscription applications will not be the cause of any build up.

If you see temporary build ups on this queue it can imply that the inbound rate is faster than the queue manager can process them. You can verify this by stopping your inbound channels and seeing if the queue drains.

However, if messages still don't drain from the queue it's possible that inbound messages have stopped being processed from that queue. This could be due to an error so check your queue manager error logs from the time that messages start to build up as this is where this would be reported.

David Ware
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SYSTEM.INTER.QMGR.PUBS queue is used for distributing publications received from a remote queue managers to local subscribers.

Messages could pile up in this queue if the queue manager is receiving publications from remote queue managers faster than it can distribute them to local subscribers.

Do you use topic host routing?

Shashi
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  • No, We do not use topic host routing. We are on MQ version 7.5 – sijo0703 Mar 14 '16 at 14:13
  • So does the SYSTEM.INTER.QMGR.PUBS gets publication messages before even they are directed to the Topics? I am trying to understand the message flow when messages comes from remote queue managers to a publish/subscribe queue manager where Topics & subscriptions are defined – sijo0703 Mar 29 '16 at 14:01