PH09282: POTENTIALLY LOTS OF LMQUEUE WAIT FOR THE XMLOCK WHEN A XPCFTCH GLUE IS BEING INVOKED.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When CICS is invoking a program or programs enabled to run at
  the XPCFTCH Global User Exit point, the XMLOCK is acquired
  Exclusive before getting some information to be put in the
  DFHUEPAR parameter list to be passed to the GLUE.  Getting the
  XMLOCK Exclusive at this point can cause excessive LMQUEUE wait
  time if there is lots of contention for the XMLOCK.  (One thing
  that can cause lots of contention for the XMLOCK is lots Starts
  for new transactions while there are thousands of transactions
  queued for TCLASS or MXT reasons.)
  .
  Here is an example of the Kernel stack of a transaction that is
  waiting on the XMLOCK while trying to invoke an XPCFTCH GLUE:
  .
  TYPE ADDRESS  LINK REG OFFSET ERR NAME
  
  Bot  2E503700 AE503CB8 0005B8     DFHKETA
  Dom  2E51F638 AE51F8CE 000296     DFHDSKE
  Dom  2E559D18 AE55B7B6 001A9E     DFHXMTA
  Dom  2EC1C098 AEC1F06C 002FD4     DFHPGPG
  Int   +0003D4 AEC1C26C 0001D4     INITIAL_LINK
  Dom  2F115600 AF11AC88 005688     DFHAPLI1
  Int   +00315E AF115FE2 0009E2     DRIVE_XPCFTCH_EXIT
  Int   +005642 AF11879A 00319A     SETUP_GLUE_PARAMETERS
  Dom  2E562450 AE5637E8 001398     DFHXMIQ
  Int   +00131C AE562630 0001E0     GET_XM_LOCK
  Dom  2E53AB28 2E53C359 001831     DFHLMLM
  Int   +0006C0 2E53AE16 0002EE     LOCK
  Int   +00104C 2E53B21E 0006F6     LOCK_EXCLUSIVE
  Int   +0007B8 2E53BC76 00114E     ADD_TO_LOCK_QUEUE
  Int   +001774 2E53B470 000948     SUSPEND
  Dom  2E512398 AE51432A 001F92     DFHDSSR
  Int   +00192E AE512E88 000AF0     POP_TASK
  .
  Not having to get the XMLOCK exclusive in this situation would
  remove a bottleneck point.  That would improve performance in
  situations such as described above.
  .
  Additional Symptom(s) Search Keyword(s): KIXREVDWZ
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users                               *
  ****************************************************************
  * PROBLEM DESCRIPTION: Poor response times and performance     *
  *                      degradation due to XMLOCK               *
  *                      contention.                             *
  ****************************************************************
  A flurry of event processing activity led to CEPD transactions
  trying to attach many thousands of tasks to process the events.
  There was a degradation in system performance and throughput as
  a result of this workload. Many of the user tasks that were
  attached were suspended in LMQUEUE waits. The lock being waited
  upon was the XMLOCK.
    The user tasks needed to get the XMLOCK exclusive when the
  initial program was being invoked.  This is because there was a
  GLUE that was enabled to run at the XPCFTCH exit point. CICS
  passes some transaction-related parameters to the exit. It
  gets the XMLOCK before getting those transaction-related
  parameters because it issues a DFHXMIQM domain call.
    In addition, the CEPD transactions need to get the XMLOCK
  exclusive when they attach a user transaction to process the
  events.
    As the TCLASS queue grows, there is some CPU intensive code
  within CICS transaction attach logic that runs while the
  XMLOCK is held. This compounded the general performance issue
  because CICS needs to run the transaction chain each time it
  goes to attach a transaction.
    The result of these factors means that getting the XMLOCK is
  a bottleneck within a CICS system as the number of CEPD
  transactions reaches several hundred. This causes the user
  transactions to have lots of Lock Delay time and
  wait-for-redispatch time.
  

Problem conclusion

• DFHAPLI1 has been changed to use an inlined DFHXMIQI call
  in place of the DFHXMIQM domain call.
  

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:

  010PC2Ÿ UI63103 UI63104 UI63105

Modules/Macros

• DFHAPLI1 DFHAPLX1 DFHAPLX3
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R000 PSY UI63103

     UP19/05/21 P F905

• R100 PSY UI63104

     UP19/05/21 P F905

• R200 PSY UI63105

     UP19/05/21 P F905

Fix is available

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