PI47486: DBD SCAN PARAMETER RANGE NOT HONOURED, OSAM DB, START POINT > 4GRANGE. SPACE MANAGEMENT UPPER RANGE UNCONSTRAINED.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A HIDAM, OSAM DB, larger than 4GB, was reloaded using an OEM
  utility. The utility set the space map flag bits to all ones
  ( indicating enough free space for largest segment ) and does
  not update them as data is loaded.
  Later, a BMP ISRTs to the database. Due to an error in DFSLLCL0,
  when the start point of the space search is a block beyond the
  4GB point, the DBD SCAN limit parameter ( which defaulted here
  to 3 CYL ) is not honoured and the space search extends to end
  of the database. In this case, this was very expensive since
  the space map bit map incorrectly indicated space was available,
  so IMS read each block, found no space, re-wrote the space
  map block, and logged it, tens of thousands of times.
  Had the SCAN parameter been honoured IMS would have immediately
  looked at end of DB, where space was available, once the 3 CYL
  range had been processed.
  Only impacts OSAM and DBs larger than 4GB.
  In many cases, this probably is never noticed, the combination
  of the OEM load process and this error were unfortunate.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All IMS V14 users with HDAM/OSAM or                          *
  * HIDAM/OSAM databases, which have one or                      *
  * more data sets larger than 4GB.  The DATASET                 *
  * statement in the DBD has no SCAN parameter                   *
  * specified.                                                   *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * BMP job hang with space manager search                       *
  * range RBN beyond the end of the                              *
  * dataset.                                                     *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * INSTALL CORRECTIVE SERVICE FOR APAR/PTF                      *
  ****************************************************************
  While a BMP is running, IMS space manager is creating and
  formatting many new extents.  The DBD statement has no SCAN
  parameter provided and the default value 3 is set correctly.
  When space manager scans for space, it should stop after 3 CYLs
  (6 CYLs if going both directions is allowed).  But it doesn't
  stop.  Due to these heavy creating, formatting and scanning
  activities, it takes a long time to find space when needed.  In
  some commit cycle, two space maps are read and updated before
  space is finally found.  Other symptoms may include excessive
  deadlocks, lock timeouts, and slow performance in updating
  databases.  There's logic in module DFSLLCL0 to prevent space
  management from going beyond 4GB or 8GB by limiting the scan
  high block range.  For an 8GB OSAM DB the existing code checks
  if the database size is > 4GB, and then sets the high scan range
  to 8GB-1 block.  This is not correct and causes many scans for
  4GB DB space to use 8GB-1 block as high range.  It should check
  if the database size >= 8GB instead and then set the high scan
  range to 8GB-1 block.
  

Problem conclusion

• GEN:
  KEYWORDS:
  
  *** END IMS KEYWORDS ***
  Module DFSLLCL0 has been modified to address the problem.  For
  8GB DB, it checks if the database size >= 8GB.  It then sets the
  high scan range to 8GB-1 block.
  

Temporary fix

Comments

APAR Information

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

  PI43292

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

  PI76722 UI45265

Modules/Macros

• DFSLLCL0
  

Fix information

• Fixed component name

  IMS V14

• Fixed component ID

  5635A0500

Applicable component levels

• R401 PSY UI45265

     UP17/03/10 P F703

Fix is available

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