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 number
IT12103
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
2015-11-10
Closed date
2015-11-20
Last modified date
2016-07-30
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:
30 July 2016