Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

The only queue that contains messages put by applications is SYSTEM.INTER.QMGR.PUBS. MAXDEPTH is set to its maximum value for this queue to allow temporary build up of published messages during outages or times of excessive load. If the queue manager is running on a system where that depth of queue could not be contained, this should be adjusted. as per the documentation.

You can use the MQ Sample browse program. It will show the PUT application. 

If MQ Console is enabled, it helps provide details.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Did you guys check whether the offending qmgr had pub/sub enabled?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Hi Francois,

The QM hosts several queues which are mostly working as expected, but as this queue is unfortunately a system queue it handles messages for all the queues associated with the QM, so it's an arduous task trying to pin down which queue is misbehaving, in answer yes all the queues use pub/sub.

we've continuing to investigate, I will put our findings here in due course.

best regards,

Gary

Did you guys check whether the offending qmgr had pub/sub enabled?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Did you guys check whether the offending qmgr had pub/sub enabled?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Hi Francois, sorry, yes, pub/sub is enabled for the QM,

we'll carry on digging, but as MQ admin is not our primary skill, may take some time and lessons to be learnt.

thanks,

------------------------------
Gary Spencer

Original Message:
Sent: Tue December 16, 2025 08:29 AM
From: Francois Brandelik
Subject: SYSTEM.INTER.QMGR.PUBS Open input count = 0 but queue depth still grows

Did you guys check whether the offending qmgr had pub/sub enabled?

------------------------------
Francois Brandelik

Original Message:
Sent: Mon December 15, 2025 04:21 AM
From: John Hawkins
Subject: SYSTEM.INTER.QMGR.PUBS Open input count = 0 but queue depth still grows

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

------------------------------
John Hawkins
Integration Consultant

Original Message:
Sent: Fri December 12, 2025 05:36 AM
From: Gary Spencer
Subject: SYSTEM.INTER.QMGR.PUBS Open input count = 0 but queue depth still grows

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

------------------------------
Gary Spencer
------------------------------

Did you guys check whether the offending qmgr had pub/sub enabled?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?

Hi Francois,

for those two it's showing:-

PSMODE(ENABLED)

APPLTAG(amqzmuf0)

and as most of the queues are working we don't want to interrupt services unnecessarily, even though we're a little bit lucky this is the non-prod system

[and ever so grateful it isn't the Prod system exhibiting this behaviour!].

anyway as I said, investigations continue

thanks for the good guidance so far,

best regards,

Did you guys check whether the offending qmgr had pub/sub enabled?

Just to add to this (for others in the future). If the connection that is putting the messages is intermittent then it would be hard to capture the exact instant the messages were increasing using e.g. explorer or mqsc commands. Activity trace would be the way to go if identifying the put application by looking at the message wasn't enough.

In the case of SYSTEM.INTER.QMGR.PUBS this is a local queue which holds messages that have come from a remote QM - so it's a little bit more nasty than usual !

regards,

John.

Hi, we don't have dedicated MQ administrators any more, I'm part of the sys admin team that inherited support for our MQ 9.3 systems using pub/sub.

We have a dev environment, plus a pre-prod IBM RDQM cluster, and a prod IBM RDQM cluster.

On one of the queue managers in the pre-prod cluster, one of the system pub/sub queue has messages filling SYSTEM.INTER.QMGR.PUBS, though curiously, and different to the other environments, open input counts is always = 0 when I look at it, so I don't understand where the messages are coming from, even after clearing the messages they soon start to fill again.

How do we find where these messages are coming from ?