MQ

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  • 1.  Reason for semaphore is busy and how to mitigate

    Posted Fri February 03, 2023 11:08 AM
    Hi,

    We recently encountered a problem on our Appliance running 8.0.0.11 where a number of clients couldn't connect for about 2 hours. The problem resolved without manual intervention. After analysing log files we noticed an "AMQ6150-W: IBM MQ Appliance semaphore is busy" error at the start and end of this period. Two FDC fles were also created showing an xecL_W_LONG_LOCK_WAIT error and a xlsRequestMutex at the beginning and xlsReleaseMutex at the end. There was no significant traffic on the machine in this period.

    Since we are still running on V8 IBM Support will not investigate this anymore, so I would like to ask the community: what could be the reason for this error and how can we fix it if we notice it next time ?

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    Frank Donkers
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  • 2.  RE: Reason for semaphore is busy and how to mitigate

    Posted Mon February 06, 2023 03:34 AM
    Hi Frank,

    I would be inclined to see if Application Activity Trace reveals a pattern:

    https://www.ibm.com/docs/en/ibm-mq/8.0?topic=network-application-activity-trace

    if it happens intermittently and you're not making any changes it might be an external event. That won't necessarily give you a fix it but might shed some light as to what triggers it.

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    Regards,

    Martin Evans
    IBM MQ Technical Product Manager
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    Original Message


  • 3.  RE: Reason for semaphore is busy and how to mitigate

    Posted Tue February 07, 2023 07:47 AM
    Thanks Martin. I think though that an activity trace is only useful if the problem is occurring, or does it also give results after the fact ? Since the problem has resolved, the queue manager has been running without problems. In fact this specific error only occurred once in over a year, so it is certainly not frequent.

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    Frank Donkers
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    Original Message


  • 4.  RE: Reason for semaphore is busy and how to mitigate

    Posted Mon February 06, 2023 05:53 AM
    Once again this issue highlights our inability to share FDC's to help more accurately identify MQ issues.
    There are obviously data integrity/security concerns around sharing too much information, but the Reason code and function names are simply not enough for any realistic analysis.
    If the information that clients "couldn't connect" is accurate (i.e MQCONN did no return ) then it would narrow things down a bit, but if it's a more general concept of "connecting" (for example application initialization, which would typically include at least on MQOPEN) then it could be a much wider range of reasons.

    There's probably no risk in posting the FDC header's, including the MQM Function stacks, which would provide a bit more insight. Similarly there's unlikely to be any risk associated with posting the trace history from the FDC's which would provide further insight.

    It's a huge leap to think that activity trace is likely to provide any insight into this issue, much better to narrow down the issue based upon the FDC content if you can get a suitably knowledgable person to help you.

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    Andrew Hickson
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    Original Message