PH13905: HIGH CPU CONSUMPTION DUE TO LOOP IN DSNXKAC1 WHEN USING -START RLIMIT SCOPE(GROUP) 19/08/15 PTF PEREMOVE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When using -START RLIMIT with SCOPE(Group) option, for any
  INSERT/DELETE/UPDATE to any table in any member, Db2 is possible
  to invoke -START RLIMIT command internally. When there are many
  internal control blocks were left as uncleaned under notify exit
  service tasks, CPU consumption will increase due to the loop in
  DSNXKAC1 to go through these control blocks.
  
  Additional Keywords:
  DB2RLF LOOPDSNXKAC1 DB2STGLK/K
  ZSA4
  

Local fix

• To clean these control blocks, Db2 restart is needed. Please
  take below steps:
  1. Issue -START RLIMIT command without SCOPE(GROUP) from all
  members. This will ensure that all members's internal flag of
  SCOPE(GROUP) is reset.
  2. Restart Db2 member by member to clean these left control
  blocks
  Please make sure to complete step 1 on all members and then
  start to restart Db2. Otherwise, if any member has the internal
  flag on for SCOPE(GROUP), then the internal -START RLIMIT on
  this member will bring to all other members.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All Db2 12 for z/OS users of the                             *
  * START RLIMIT SCOPE(GROUP) command                            *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * High CPU consumption due to loop                             *
  * in DSNXKAC1 when using                                       *
  * -START RLIMIT with the SCOPE(GROUP)                          *
  * option                                                       *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply corrective PTF when available                          *
  ****************************************************************
  When the -START RLIMIT with SCOPE(Group) option is used, a
  subsequent INSERT/DELETE/UPDATE to the active RLF table
  triggers the refresh of the in-memory RLF table in each member
  of the data sharing group. The auto refresh process in members
  where the update was not done left internal control blocks when
  looking up Db2 catalog table to verify the active RLF table.
  When many of these internal control blocks were left as
  uncleaned under the notify exit service tasks, CPU consumption
  will increase due to the loop in DSNXKAC1 to go through
  these control blocks.
  

Problem conclusion

• Db2 code has been changed to release storage when looking up
  catalog to refresh the in-memory RLF table in the notify exit.
  Additional keywords: RLF
  

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:

  UI65580

Modules/Macros

• DSNTCSRC
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI65580

     UP19/10/15 P F910 ¢

Fix is available

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