PM75408: ODBA THREADS FROM DB2 STORED PROCEDURE MAY HANG.

A fix is available

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APAR status

  • Closed as program error.

Error description

  • IMS receives DPSB PREP call from an ODBA WLM Stored Procedure.
    While processing the DPSP PREP call, the IMS Backout exit is
    driven asynchronously as the result of the context owner
    abruptly ending the context (terminating syncpoint).  This
    asynchronous event results in IMS doing Terminate Thread
    processing against the ODBA Thread at the same time DPSB PREP
    processing is active.  This may result in potential timing
    conditions which may appear as hung ODBA Threads.
    .
    Additional symptoms: abendu0768 rc02 due to the saps1swt flag
      If the DPSB Prep process (DFSDAST0) and Syncpoint process
      (DFSSYI50) ran in parallel and both processes issued the
      ISWITCH calls on the same SAP/ECB, it is possible set the
      saps1swt flag on incorrectly. Later when another process
      issued an ISWITCH on the ECB, IMS could abend u0768 RC02.
    

Local fix

  • N/A
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All IMS V11 ODBA and/or ODBM RRS=Y users     *
    *                 that run IMS application programs that issue *
    *                 the DPSB PREP call.                          *
    ****************************************************************
    * PROBLEM DESCRIPTION: A hung thread condition can result if   *
    *                      IMS is driven for a terminating         *
    *                      syncpoint Backout while in the midst    *
    *                      of processing an application DPSB PREP  *
    *                      call.                                   *
    *                                                              *
    *                      Additional Symptoms known to occur:     *
    *                                                              *
    *                      - ABENDS0C4 in DFSRRSI0, while FRR is   *
    *                        active, during End Context function   *
    *                        processing.                           *
    *                                                              *
    *                      - ODS TCB ABENDS0C6                     *
    *                                                              *
    *                      - IMS Dispatcher abends ABENDU0766      *
    *                        and ABENDU0768                        *
    *                                                              *
    ****************************************************************
    * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
    ****************************************************************
    While Phase 1 syncpoint processing was in progress for an active
    ODBA application that just issued an DPSB PREP call, call, IMS's
    Backout Exit is driven by RRS instructing that the ODBA thread
    be aborted.  Backout was initiated by RRS due to a terminating
    syncpoint condition resulting from the thread TCB abending.  The
    TCB abend stemmed from the active context being abruptly ended
    by its owner (not IMS).
    
    The asynchronous Backout request from RRS exposed a timing
    condition weakness within IMS that allowed DPSB PREP initiated
    Phase 1 syncpoint to run concurrently with RRS syncpoint Backout
    processing.
    
    With both syncpoint processes running in parallel and utlilizing
    the same control blocks (i.e. DPST, LCRE, Save Areas, etc...),
    the potential exists that any of these control blocks could be
    updated by either syncpoint process at the same time.
    
    Depending upon which control blocks become affected, the control
    block data being updated, and the timing in which updates occur,
    failures could result in IMS code during any interval of DPSB
    PREP during DPSB PREP or and/or syncpoint Backout processing.
    Problems that have been known to occur as a result are:
    
     - ABENDS0Cx (0C4, 0C6)
     - IMS Dispatcher type abends ABEDU0766 and ABENU0768
    
    *************************************************************
    It is important to make note that the IMS failures that could
    occur as a result of this reported problem are NOT limited to
    those identified above.
    *************************************************************
    
    
    Additional keywords: ABEND0C6 0C6 S0C6 ABEND0C4 S0C4 0C4
                         U0766 U766 U0768 U768
    

Problem conclusion

  • GEN:
    KEYWORDS:
     SYSPLEXDS
    
    *** END IMS KEYWORDS ***
    To eliminate the parallel processing exposure between IMS DPSB
    PREP Phase 1 syncpoint and RRS syncpoint Backout, the design of
    DPSB PREP processing has been modified.
    
    Effective with this service, IMS will not longer internally
    perform Phase 1 (PREPARE) syncpoint processing as part of the
    DPSB PREP application call. Phase 1 syncpoint will now be
    performed by IMS when called directly by RRS to perform PREPARE
    processing.
    
    To support this change, IMS code has been modified as follows:
    
    1. DFSDAST0 - removed initiating the IMS Phase 1 sync request.
    
    2. DFSRRSI0 - enables ODBA PREPARE processing with RRS when
                  driven by RRS to perform syncpoint Phase 1.
    
    3. DFSAERC0 - updated to accomodate RRS PREPARE syncpoint
                  processing and to alleviate control block
                  block referencing between IMS ODBA syncpoint
                  phases.
                  For awod_ods_sync_comp processing, the RRS PDUE
                  call will now be done by DFSAERN0.
    
    4. DFSAERN0 - upon completion of awod_ods_sync_comp processing,
                  RRS Post_Deferred_ UR (PDUE) processing will now b
                  performed.
    
    5. DFSAERS0 - establish DFSRRSI0 PDUE call structure for
                  DFSAERN0.
    
    6. DFSODSYN macro - When an awod_ods_sync_comp request,
                        ensure RRS PUE call is initiated by
                        DFSAERN0.
    
    7. DFSODMWK macro - define new byte ods_flag2 and bits
                        ODS_F2_LCREUNHK and ODS_F2_LCRECDRA
                        for DFSAERC0 PLX usage.
                        Additional parameters defined to support
                        PDUE call structure from DFSAERN0.
    
    8. DFSDAWE macro  - define new ODS TCB sub-function
                        AWOD_TCBSF_PDUE to support PDUE call
                        from DFSAERN0.
    

Temporary fix

  • *********
    * HIPER *
    *********
    

Comments

APAR Information

  • APAR number

    PM75408

  • Reported component name

    IMS V11

  • Reported component ID

    5635A0200

  • Reported release

    100

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-10-18

  • Closed date

    2013-07-12

  • Last modified date

    2013-08-02

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

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

    PM83193 UK95803

Modules/Macros

  • DFSAERC0 DFSAERN0 DFSAERS0 DFSDAST0 DFSDAWE  DFSRRSI0
    

Fix information

  • Fixed component name

    IMS V11

  • Fixed component ID

    5635A0200

Applicable component levels

  • R100 PSY UK95803

       UP13/07/17 P F307 ½

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


More support for:

IMS

Software version:

100

Reference #:

PM75408

Modified date:

2013-08-02

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