IT38527: MQTT component MQXR service produces an unnecessary Java dump aspart of the FFST generation.

APAR status

• Closed as program error.

Error description

• A customer port scan of MQXR service ports caused the production
  of FFST's
  because of the invalid data placed on the port by the scanning
  tool.
  
  As a part of creating the FDC record documenting the issue the
  MQXR
  service creates a Java thread dump.  This is unnecessary and
  consumes
  system resources creating a potential performance impact for
  MQTT clients.
  
  Sample MQXR FDC probeid's resulting in the dumps.
  XR071001 XR071024 XR054001
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  Users of MQTT and thus MQXR that are perhaps seeing/generating
  malformed packets on the MQXR port.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  When MQTT (MQ Telemetry) is enabled on a Queue Manager, the MQXR
  (MQ Extended Reach) service is started, in order to facilitate
  communication between MQ and an MQTT enabled client. MQXR opens
  UDP ports in order to allow for the communication to happen.
  MQXR operates on port 1818, and expects correctly formed MQTT
  packets on this socket. If the packets that are received are
  malformed or unexpected, then MQXR handles this by generating an
  FDC (Failure Data Capture).
  
  In the process of generating this FDC a Java core dump is also
  generated, in order to provide extra information to facilitate
  debugging. These files can be very large in size and take a fair
  amount of time to generate. In order for the JVM (Java Virtual
  Machine) to generate these thread dumps, it is necessary to
  pause all the running threads, in order to take a snapshot of
  their current state. This can slow down execution of the Queue
  Manager for a noticeable amount of time.
  
  It is unnecessary to generate these Java core dumps upon
  generation of every FDC.
  

Problem conclusion

• An extra system property/flag has been introduced in order to
  enable or disable the generation of these Java core dumps
  alongside FDC's. The flag itself is named
  com.ibm.mq.MQXR.GenerateJavaDump and located at
  'mqinstall/qmgrs/qmgr_name/mqxr/java.properties' as well as
  'mqinstall/qmgrs/qmgr_name/amqp/amqp_java.properties' of your MQ
  installation. It is advised that both of these properties be set
  to the same value to preserve system stability.
  
  This property is of type String (case insensitive), but parsed
  as a boolean, as such the value can only be set to either "true"
  or "false". The default value of this property is "false", and
  as such it does not need to be set/present in the properties
  files in order for the behaviour of not generating Javacores to
  be enabled.
  
  Documentation for this new property can be found at
  https://www.ibm.com/docs/ibm-mq/9.2?topic=troubleshooting-locati
  on-telemetry-logs-error-logs-configuration-files
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.2 LTS   9.2.0.5
  v9.x CD    9.2.5
  
  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 is sysrouted FROM one or more of the following:

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

Fix information

• Fixed component name

  MQ BASE V9.2

• Fixed component ID

  5724H7281

Applicable component levels