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IT20441: Subscribing MQTT client to more than 100 topics in a single subscribe call causes FDC and client to be disconnected

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APAR status

  • Closed as program error.

Error description

  • When attempting to subscribe to more than 100 topics in a single
    MQTT subscribe call, the client is disconnected and an FDC is
    generated with:
    
    Probe Id          :- XR055005
    
    and exception and stack:
    
    java.lang.IllegalStateException: MQTTWireContext repeated
    retry:RETRY
    	at
    com.ibm.mq.MQXRService.MQTTWireContext.receive(MQTTWireContext.j
    ava:403)
    	at
    com.ibm.mq.communications.NonBlockingConnection.receive(NonBlock
    ingConnection.java:378)
    	at
    com.ibm.mq.communications.NonBlockingWorker.run(NonBlockingWorke
    r.java:339)
    	at java.lang.Thread.run(Thread.java:809)
    
    The last entries in the history will be subscribes, for example:
        2 Tue Oct 24 15:09:16 BST 2017 RECEIVED_MQTT
    mqttMessageType:SUBSCRIBE
        3 Tue Oct 24 15:09:16 BST 2017 RECEIVED_MQTT
    mqttMessageType:SUBSCRIBE
    
    If this is traced, the trace will show a
    TransactionFullException being generated:
    
    13.59.46.738   31  @XXXXXXXX
    com.ibm.mq.MQXRService.MQTTServerSessionV3
          ----+---- { receiveSubscribe
    [com.ibm.mqttv3.internal.MQTTSubscribe@XXXXXXXX] [SUBSCRIBE] [1]
    [clientID]
    13.59.46.738   31  @XXXXXXXX
    com.ibm.mq.MQXRService.MQTTServerSessionV3
          ----+----+ { registerSubscriptions
    [com.ibm.mqttv3.internal.MQTTSubscribe@XXXXXXXX]
    13.59.46.738   31
    com.ibm.mq.MQXRService.MQXRServiceException
          ----+----+- { <init>
    [com.ibm.mq.MQXRService.TransactionFullException]
    [com.ibm.mq.MQXRService.MQTTServerSessionV3@XXXXXXXX,clientident
    ifier=clientID,conname=X.X.X.X] [class
    com.ibm.mq.MQXRService.TransactionFullException]
    13.59.46.738   31
    com.ibm.mq.MQXRService.MQXRServiceException
          ----+----+- } <init>
    [com.ibm.mq.MQXRService.TransactionFullException]
    13.59.46.738   31  @XXXXXXXX
    com.ibm.mq.MQXRService.MQTTServerSessionV3
          ----+----+ } registerSubscriptions [%C%]
    [com.ibm.mq.MQXRService.TransactionFullException]
    13.59.46.738   31  @XXXXXXXX
    com.ibm.mq.MQXRService.MQTTServerSessionV3
          ----+---- } receiveSubscribe [%C%]
    [com.ibm.mq.MQXRService.TransactionFullException]
    

Local fix

  • Ensure that each subscribe action has less number of topics
    then the value of  maximumSubscriptionOperationsPerBatch
    

Problem summary

  • ****************************************************************
    USERS AFFECTED:
    This issue affects users trying to subscribe an MQTT client to
    more than 100 topics in a single subscribe call
    
    
    Platforms affected:
    MultiPlatform
    
    ****************************************************************
    PROBLEM DESCRIPTION:
    When an MQTT client tried to subscribe to more than 100 topics
    in a single subscribe call, this failed, causing an FDC with
    probe XR055005 to be generated, and the client to be
    disconnected. This was because of a hard-coded limit to the
    number of topics that could be subscribed to in a single
    subscribe call by an MQTT client. This limit could not be
    modified.
    

Problem conclusion

  • The limit to the number of subscriptions that can be made in a
    single MQTT subscribe call is now configurable - so if the user
    intends to subscribe to more than 100 topics in a single
    subscribe call this limit can be increased to allow this.
    
    To modify the limit, set the following property:
    
    com.ibm.mq.MQXR.MaximumSubscriptionOperationsPerBatch=<required
    value>
    
    in the MQXR properties file:
    
    <MQ_DATA_DIRECTORY>/qmgrs/<QUEUE_MANAGER_NAME>/mqxr/mqxr_unix.pr
    operties
    
    for Linux, or the mqxr_win.properties file at the same directory
    for Windows.
    
    Note that the default value for the maximumOperationsPerBatch
    property - which specifies the total operations per batch, not
    just subscriptions - is 500. If setting the value of
    MaximumSubscriptionOperationsPerBatch to more than 500, the
    value of maximumOperationsPerBatch will also have to be
    increased to that higher value, by setting the property:
    
    com.ibm.mq.MQXR.MaximumOperationsPerBatch=<required value>
    
    in the same properties file as the
    MaximumSubscriptionOperationsPerBatch property is set.
    
    ---------------------------------------------------------------
    The fix is targeted for delivery in the following PTFs:
    
    Version    Maintenance Level
    v8.0       8.0.0.9
    v9.0 CD    9.0.5
    v9.0 LTS   9.0.0.3
    
    The latest available maintenance can be obtained from
    'WebSphere MQ Recommended Fixes'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
    
    If the maintenance level is not yet available information on
    its planned availability can be found in 'WebSphere MQ
    Planned Maintenance Release Dates'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
    ---------------------------------------------------------------
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT20441

  • Reported component name

    WMQ BASE MULTIP

  • Reported component ID

    5724H7251

  • Reported release

    800

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2017-05-03

  • Closed date

    2017-12-04

  • Last modified date

    2017-12-04

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    WMQ BASE MULTIP

  • Fixed component ID

    5724H7251

Applicable component levels

  • R800 PSY

       UP

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Document Information

Modified date:
04 December 2017