PI88681: PERFORMANCE DEGRADATION USING MSC BANDWIDTH LINKS IN AN IMS SHARED QUEUES ENVIRONMENT.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• In an IMS Shared Queues environment if Bandwidth is used for an
  MSC link there can be a severe performance degradation.  IMS
  UOWE control blocks are allocated but never freed.  This leads
  to searching long chains of UOWE's and holding latches for an
  extended period when adding or deleting UOWE's.  This occurs on
  both ends of the MSC link.  The problem can also lead to a
  shortage of ECSA storage.
  
  Bandwidth is the only option for TCP/IP MSC links and is
  optional for VTAM MSC links.
  

Local fix

• Use VTAM MSC links without the Bandwidth option when either side
   of the MSC link is an IMS shared queue environment.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All V14 IMS users of shared queues who                       *
  * have MSC TCP/IP links, or who have MSC                       *
  * VTAM links and are using bandwidth mode.                     *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Depending on the volume of the                               *
  * workload, users may experience system                        *
  * performance degradation and a shortage                       *
  * of ECSA storage.                                             *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * INSTALL CORRECTIVE SERVICE FOR APAR/PTF.                     *
  ****************************************************************
  In an IMS Shared Queues environment with either MSC TCP/IP links
  (which always use bandwidth mode), or with MSC VTAM links with
  bandwidth mode enabled, the message queue read processor does
  not release an internal block as expected on the completion of
  the message reading.  The control block represents a unit of
  work and is used for recovery purpose in case of a failure.  As
  a result, these control blocks accumulated in a chain in storage
  and any operation on the chain is time consuming and impacts the
  system performance.
  

Problem conclusion

• DFSQGU00 - IMS queue manager GU / GN command processor.
  
  In the handlers of return code 8, 28, and 32 for the GU (get
  unique) command processor, removed the decision of keeping the
  QMBA / QMBS and UOWE blocks if the caller is MSC with bandwidth.
  The subsequent call of the FREE_QMBA subroutine can
  release the UOWE block upon request.
  
  In the FREE_QMBA subroutine, added the decision of keeping the
  QMBA / QMBS block if the caller is MSC with bandwidth.
  

Temporary fix

Comments

APAR Information

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

  PI88557

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

  UI51618

Modules/Macros

• DFSQGU00
  

Fix information

• Fixed component name

  IMS V14

• Fixed component ID

  5635A0500

Applicable component levels

• R400 PSY UI51618

     UP17/11/11 P F711 ¢

Fix is available

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