IT12103: IBM MQ 8.0 A LARGE NUMBER OF GHOST QUEUES GET CREATED WHEN STATQ IS ENABLED.

APAR status

• Closed as program error.

Error description

• When using IBM MQ V8 and queue statistics (STATQ) are enabled
  for dynamic queues, a
  large number of ghost queues get created. In the filesystem
  under the queue manager directory 'queues' more than thousand
  ghost queues like the following may appear:
  
  !!GHOST!4269DF61!0!1A11DF21!13608
  

Local fix

• Disable STATQ for dynamic queues (via the associated model
  queues).
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects MQ V8 customers with STATQ resolving to ON
  for a model queue, and therefore for the associated dynamic
  queues. Customers not using dynamic queues are not affected.
  The issue leads to a much larger pool of ghost queues, and
  therefore more file system objects being associated with a queue
  manager.
  It's not a true leak as such as the working set of ghost queues
  will stabalize. There will be a lower rate of reusing of ghost
  queues (to instantiate dynamic queues), but as the performance
  of creating dynamic queues is so much better in MQ V8 this may
  not have a noticeable effect on performance.
  
  
  Platforms affected:
  AIX, HP-UX Itanium, IBM iSeries, Linux on Power, Linux on S390,
  Linux on x86, Linux on x86-64, Linux on zSeries, Solaris SPARC,
  Solaris x86-64, Windows
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  When a dynamic queue is first created, a 'ghost' queue file is
  allocated an initialized to store the attributes and data
  associated with that dynamic queue. When the dynamic queue is
  deleted the 'ghost' queue file is not deleted, but added to a
  cache of such queues associated with the relevant model queue.
  When a dynamic queue is next created based upon that model then
  rather than re-allocating and initializing a new queue file, the
  pre-existing 'ghost' queue file is used to instantiate the new
  dynamic queue.
  
  A previously used dynamic 'ghost' queue cannot be reused until
  all references to the previously used instance of the dynamic
  queue have been released. A typical example of such a reference
  would be is some application had a handle (hObj) open on the
  dynamic queue. There are also a range of possible internal
  references to the dynamic queue, and one of these is related to
  the inheritance of STATQ from the associated model queue.
  
  The reference caused by an effective STATQ of ON was being
  released at the end of each statistics internal, rather than
  when all open handles (hObj's) had been closed (MQCLOSE). The
  effect of this unintended change in V8 was that each ghost queue
  could only be used once in each statistics interval, leading to
  a very large pool of ghost queues being required to effect any
  reuse of these objects.
  

Problem conclusion

• The queue manager logic has been updated so that the ghost queue
  is available for reuse once all open handles have been closed,
  regardless of the effective value of STATQ.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v8.0       8.0.0.5
  
  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

  WMQ BASE MULTIP

• Fixed component ID

  5724H7251

Applicable component levels

• R800 PSY

     UP