PM15220: PSB POOL CASTOUT PERFORMANCE ISSUE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer has a very large number of PSBs in application suite.
  Current PSB pool castout Phase 1 processing will not consider
  a PSB for castout if it is the only copy of the PSB in the
  pool, even if otherwise it is the best candidate.
  In customer's case, old BMP PSBs left in the pool cause this
  issue, forcing the much more expensive Phase II of castout
  to be called. This apar will alter the algorithm to remove
  the 'only-copy' check if ACBIN64 ( 64-bit cache for ACBLIB )
  is in effect.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All IMS V11 users of ACB in 64-bit storage   *
  *                 (i.e. ACBIN64 parameter specified during     *
  *                 system definition) are affected.             *
  ****************************************************************
  * PROBLEM DESCRIPTION: User noticed large PSBs in the PSB pool *
  *                      that are infrequently used are never    *
  *                      selected for casting out.  Instead,     *
  *                      other more frequently used PSBs get     *
  *                      cast out.  Consequently, there is a     *
  *                      performance impact due to high used     *
  *                      transactions being a victim of          *
  *                      cast out.                               *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
  The PSB pool cast out algorithm selects old PSBs for cast out
  if they are large enough to make space for the PSB that wants
  to come into the pool, and if either of the following conditions
  is met: it's the oldest PSB in the pool or it's not the only
  copy of that PSB in the pool.
  
  In the user's case, there are many PSBs that are the only copy
  of the PSB in the pool, which prevent them from being cast out
  even though they are the best candidate otherwise.
  As a result, the more frequently used PSBs become candidates
  for cast out and cause performance degradation.
  
  This algorithm can be enhanced for users who have ACBs in
  64-bit storage since it's fast to bring PSBs back from the
  cache.
  

Problem conclusion

• GEN:
  KEYWORDS:
  
  *** END IMS KEYWORDS ***
  Module DFSDLMP0 has been changed to enhance the PSB cast out
  algorithm.  If user is running with 64-bit caching turned
  on, always cast out the least recently used PSB that is big
  enough, regardless if it is the only copy of that PSB in the
  pool.  It will be fast to bring the PSB back from the cache
  if it is needed again.
  
  If 64-bit caching is not turned on, then use the old algorithm
  (i.e. if the PSB is the oldest of all PSBs, cast it out;
  otherwise, cast it out only if it is not the last copy of that
  PSB).
  

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:

  UK60191

Modules/Macros

• DFSDLMP0
  

Fix information

• Fixed component name

  IMS V11

• Fixed component ID

  5635A0200

Applicable component levels

• R100 PSY UK60191

     UP10/09/09 P F009 Ž

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.