PK66826: IMS CONTROL REGION HANGS WHEN DYNALLOC FOR SLDSREAD FUNCTION HASTO WAIT

APAR status

• Closed as program error.

Error description

• IMS May get into a hang when the dynammic allocation for a SLDS
  needed for backout has to wait.
  The way it whas recreated is :
  - a bmp does a few updates to a DB and then waits .
  - olds are switched a few time so the updates for
    the bmp are no longer on it .
  - another job is started that allocates the SLDS holding
    the bmp's updates .
  - the BMP abends , the SLDS read functionality in IMS
    tries to allocate the SLDS, but has to wait for the job .
  - another  /swi olds command is issued
  IMS now hangs .
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All IMS V9R1 users that use the SLDSREAD     *
  *                 function.                                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: If IMS must wait for dynamic allocation *
  *                      to read a SLDS, other IMS work may hang *
  *                      until the SLDS is allocated.            *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
  Dynamic allocation acquires an exclusive enqueue on resource
  SYSZTIOT.  Any other OPEN, CLOSE, or DYNALLOC request in the
  same address space will wait until this enqueue is released.
  When IMS needs to read data from a SLDS, it issues a dynamic
  allocation request through the DFSMDA service and the SYSZTIOT
  resource is held until the SLDS is obtained.  Many other IMS
  activities involve OPEN, CLOSE, or DYNALLOC so the probability
  of an impact to IMS function is high.
  

Problem conclusion

• AIDS: RIDS/SYS RIDS/LOG SYS LOG
   GEN:
  POSTREQ PK82047 + PK87345
  KEYWORDS:
  
  *** END IMS KEYWORDS ***
  The SLDS read function has been changed to issue its own dynamic
  allocation requests under the subtask it uses for OPEN and
  CLOSE.  It should be noted that, as a consequence, the DFS2500I
  ( MSGDFS2500I ) messages for SLDS allocations to DD name IMSLOGR
  will no longer be seen because they are issued by the DFSMDA
  service which is no longer used.  It should also be noted that
  the UNIT information from DBRC was being ignored by DFSMDA and
  this has been corrected.  This may introduce errors in SLDS
  allocation if the UNIT value in the PRISLD record is invalid.
  
  The logger timer subtask module, DFSFDLD0, has been changed to
  check for SYSZTIOT contention by using the GQSCAN service.  If
  any waiters for the SYSZTIOT resource are detected for two
  successive timer periods, DFSFDLD0 will issue CALLRTM to
  terminate the logger subtask that issued the allocation request.
  This is expected to allow other SYSZTIOT requestors to use
  and release the the resource.  SLDS read will then re-attach
  its subtask and re-issue the SLDS allocation request.
  
  In the event that the delete and re-attach of the SLDS read
  subtask does not eliminate SYSZTIOT waiters, DFSFDLD0 and SLDS
  read will repeat the process up to three times.  If the number
  of waiters still does not drop to zero, SLDS read will fail.
  

Temporary fix

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

Comments

• REPINNED RP09/03/06 (ATXT) TO ADD POSTREQ PK82047 INFO.
   **** PE09/03/06 PTF IN ERROR. SEE APAR PK82047 FOR DESCRIPTION
  REPINNED RP09/05/26 (ATXT) TO ADD POSTREQ PK87345 INFO.
   **** PE09/05/26 PTF IN ERROR. SEE APAR PK87345 FOR DESCRIPTION
  ×**** PE09/05/26 FIX IN ERROR. SEE APAR PK87345  FOR DESCRIPTION
  

APAR Information

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

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

  PK76926 UK42926

Modules/Macros

• DFSFDLD0 DFSFDLG0 DFSFDLS0 DFSFLLG0 LCDSECT
  

Fix information

• Fixed component name

  IMS V9

• Fixed component ID

  5655J3800

Applicable component levels

• R900 PSY UK42926

     UP09/01/16 P F901 Ž