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PK58570: TASKS STUCK IN ROLLING CONTENTION FOR THE PROGRAM LOCK OF A PARTICULAR PROGRAM. TASKS IN LMQUEUE AND PROGRAM WAITS.

A fix is available

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APAR status

  • Closed as program error.

Error description

  • A particular program is EXEC CICS LINKed or XCTL to very
    frequently, often multiple times per task.  The tasks doing
    this are all running on their own Open TCB and there are
    ample logical processors in the LPAR so that these Open TCBs
    can indeed run concurrently.  In an environment like this, if
    something causes many tasks to invoke the program at the same
    time, it is possible that the resulting contention for that
    program's Program lock can be great.  It can be so great that
    invocations of this program are slowed so much that it becomes
    a bottleneck point that slows response time and decreases
    throughput.
    .
    In a dump taken during this situation, there will be lots of
    tasks either in LMQUEUE waits waiting for the PGLOCK or in
    PROGRAM waits all for the same program.  The 'PGWE Summary' in
    PG=1 shows a significant number of PGWEs all for the same
    program.
    

Local fix

  • To break out of this situation, limit the number of concurrent
    tasks temporarily.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All.                                         *
    ****************************************************************
    * PROBLEM DESCRIPTION: CICS slowed down when the same PROGRAM  *
    *                      was LINK'd to concurrently by           *
    *                      transactions running on open TCBs.      *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    If a PROGRAM is locked, then a subsequent access of the same
    PROGRAM is SUSPEND'd and a PGWE is added to the PGWE chain.
    When the lock owner releases the lock, if there are any
    waiters, all the tasks on the PGWE chain for this PROGRAM are
    RESUME'd. Only one task can win the race for the PROGRAM lock
    and then all other tasks end up on the PGWE chain again.
    In a very busy CICS, when this happens, the resulting thrashing
    can be detrimental to task throughput.
    This problem is only exposed when the tasks are running on open
    TCBs.
    Keyword: PERFM
    

Problem conclusion

  • DFHPGCM release_program_lock has been changed to invoke a new
    refstep, resume_single_waiter.
    

Temporary fix

  • FIX AVAILABLE BY PTF ONLY
    

Comments

APAR Information

  • APAR number

    PK58570

  • Reported component name

    CICSTS V3 Z/OS

  • Reported component ID

    5655M1500

  • Reported release

    400

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2007-12-20

  • Closed date

    2008-03-10

  • Last modified date

    2008-04-01

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

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

    PK60174 UK34404 UK34405

Modules/Macros

  •    DESPGAI  DESPGCM  DESPGDD  DESPGEX  DESPGIS
    DESPGLD  DESPGLK  DESPGLU  DESPGPG  DESPGRP  DFHPGAI  DFHPGDD
    DFHPGEX  DFHPGIS  DFHPGLD  DFHPGLE  DFHPGLK  DFHPGLU  DFHPGPG
    DFHPGRE  DFHPGRP  DFHPGXE
    

Fix information

  • Fixed component name

    CICSTS V3 Z/OS

  • Fixed component ID

    5655M1500

Applicable component levels

  • R400 PSY UK34404

       UP08/03/14 P F803

  • R500 PSY UK34405

       UP08/03/14 P F803

Fix is available

  • Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.

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Document Information

Modified date:
01 April 2008