PI14696: DSNSCON2 ABEND0C4 CONTRACTING 64BIT VARIABLE POOL OR ABEND04E RC00E20005 AT DSNSVSPP +09D6 OFFSET09D6 14/06/24 PTF PECHANGE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• DSNSCON2 abend0c4 during contraction of an 64bit pool, in this
  case the SQL ARRAY POOL 4G which is a DB2 system level pool.
  .
  This is a PE fixing APAR for PM86952/UK97692 V10
  PM95296/UK98204 V11
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All DB2 V10 and higher                       *
  ****************************************************************
  * PROBLEM DESCRIPTION: Abend0c4 in dsnscon2 while contracting  *
  *                      a system level Above-the-bar pool. In   *
  *                      this case it was the SQL ARRAY POOL 4G  *
  *                      which is a Shared Storage pool but may  *
  *                      occur on any 64bit ATB pool.            *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  While contracting an ATB shared storage pool, an abend0c4 occurs
  when DSNSCON2 runs out of forward pointers before the search
  condition has been satisfied. The pool has multiple consecutive
  segments which are eligible for contraction, beginning with the
  anchor segment.  However, just as the pvts blocks are being
  removed from the xslot_segchain, additional pvts have been
  pushed onto the anchor and the Compare and Swap fails.  The
  subsequent logic to find position and dechain the eligible
  segments is incorrect, leaving a contracted segment pvts on the
  chain.  Though the pvts is still chained, the actual segment is
  freed and available for reuse by any thread.  Next time this
  same pool is contracted, it will likely abend0c4.
  This will only fail for 64 bit pools which are shared,
  such as system level pools, since non-shared pools should not
  have expansions while being contracted. However, the segment
  which has been freed may be picked up by ANY thread and result
  in an abend by that thread also. Also, if the DB2 is under
  full system contraction, this failure may occur even for
  non-shared pools since the contraction is done in parallel
  by a system thread. ***NOTE*** If the contracted segment is
  picked up by a thread and used for THIS POOL xslot expansion,
  it may result in an infinite loop and HIGH CPU in DBM1 starting
  with the next contraction of this pool xslot.
  

Problem conclusion

• Code has been changed to properly dechain eligible segments from
  the pool xslot_segchain.
  

Temporary fix

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

Comments

APAR Information

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

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

  UI17409 UI17410

Modules/Macros

• DSNSCON2
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RA10 PSY UI17409

     UP14/05/10 P F405 ½

• RB10 PSY UI17410

     UP14/05/10 P F405 ½

Fix is available

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