PI42276: EXCESSIVE L8 AND L9 TCBS ATTACHED. OPEN POOL STATISTICS SHOW PEAK ATTACHED IS 295 BUT PEAK USED IS 42

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Dispatcher OPEN Pool Statistics show lots more TCBs attached
  than used.  Here is an example:
  .
                Max   Current      Peak   Current      Peak
  TCB      TCB Pool      TCBs      TCBs      TCBs      TCBs
  Pool        Limit  Attached  Attached    In Use    In Use
  -----  ---------- --------- --------- --------- ---------
  OPEN          632       153       295         1        42
  .
  The corresponding Dispatcher Mode statistics for L8 and L9
  modes look like this:
  .
  TCB       TCB  < TCBs Attached >  <- TCBs In Use ->    TCB
  Mode Open Pool Current      Peak  Current      Peak Attaches
  ____________________________________________________________
   L8   Yes Open     139       275        1        41      324
   L9   Yes Open      14        20        0         6       70
  .
  These statistics have not been reset since CICS started.  So it
  could not be that a high TCBs 'In Use' number from a prior
  interval is why so many TCBs are attached.
  .
  Also, Traniso is active.
  .
  A frequently used transaction usually does its work using just
  the QR and an L8 TCB.  But sometimes, this transaction uses the
  QR and an L8 and an L9.  Once that happens there can be lots of
  attaches of L8 TCBs.
  
  
  
  
  
  
  
  
  Additional Symptom(s) Search Keyword(s): KIXREVDWZ
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Excessive numbers of open TCBs are      *
  *                      allocated when running with             *
  *                      TRANISO=YES.                            *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  CICS is running with Transaction Isolation active. It can be
  observed from the CICS monitoring and statistics data that the
  number of open TCBs (mode L8 and L9) which have been allocated
  is much greater than the total number which have been in use at
  any one time.
  This occurs because the transaction history of a particular
  transaction suggests that may require both an L8 and L9 TCB.
  The L9 TCB is needed in a very small minority of instances.
  CICS maintains a number of different pools of subspaces with
  different types of TCB attached. There are very few subspaces
  with both L8 and L9 TCBs in existence, yet the CICS subspace
  allocation algorithm chooses this as the optimum pool. When
  there are no subspaces available in this pool, CICS will create
  a new subspace.
  In the reported instance, it is very likely that CICS will
  create an L8 TCB for this subspace, but no L9 will be needed.
  When the task completes, this new subspace (having only an L8
  TCB) will be put back into the pool of available subspaces with
  an L8 TCB. The pool of subspaces with an L8 and L9 TCB continues
  to be the prime choice, but is no more likely to have any
  available subspaces.
  

Problem conclusion

• DFHSMSU has been modified in the algorithm used to allocate
  subspaces. If the first pool chosen has no available subspaces,
  CICS will check again for other pools of subspaces, which might
  be sufficient.
  

Temporary fix

• FIX AVAILABLE BY PTF ONLY
  

Comments

APAR Information

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

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

  UI29719 UI29720

Modules/Macros

• DFHSMSU
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R800 PSY UI29719

     UP15/07/31 P F507

• R900 PSY UI29720

     UP15/07/31 P F507

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.