IT31317: DB2 : MISSING DATA ON QUERY WITH CURRENTLY COMMITTED FEATURE, WHEN SUCH QUERY IS EXECUTED IN THE MIDDLE OF COMMIT PROCESSING

APAR status

• Closed as fixed if next.

Error description

• You may observe that if there are some transactions running
  alongside each other, accessing from tables in which data is
  being inserted or updated, some data might be missing. You will
  eventually see the complete data on later accesses.
  
  Example to explain the problem:
  ------------------------------
  Given :
  Transactions : UOW1 and UOW2
  Tables       : T1 and T2
  
  Working :
  1. UOW1 INSERTs/UPDATEs data in T1
  2. UOW1 INSERTs record in T2, suggesting INSERT/UPDATE to T1 is
  complete
  3. UOW2 SELECTs from T2 if it has a record, if yes, SELECTs *
  from T1
  
  Problem :
  UOW1 performs INSERT/UPDATE on T1, then INSERT/UPDATE T2 to
  indicated the new data in T1.
  
  UOW2 queries T2 (possibly in a loop) for indication of new data
  in T1, then when it sees the indication in T2 by UOW1, SELECT
  from T1 for the new data, but does not see all of the changes in
  T1 made by UOW1.  Later on SELECT from T1 will eventually see
  all the changes made by UOW1.
  
  Explanation :
  
  Lock attributes are used to implement currently committed
  feature.  It means that queries will not be blocked when seeing
  uncommitted changes.  However, during COMMIT processing, locks
  are released serially.  If another transaction executes SELECT
  during the COMMIT processing, in particular when some but not
  all of the locks acquired by the committing transaction have
  been released, the SELECT will see some but not all of the
  changes.
  
  Note: the issue may be more pronounced in pureScale.
  
  NOTE: In order for the fix to take effective, you will also need
  to turn on the Db2 registry variable
  DB2_SYNC_RELEASE_LOCK_ATTRIBUTES after applying the fix and
  changes to this variable do not require the database instance to
  be restarted:
  
  db2set DB2_SYNC_RELEASE_LOCK_ATTRIBUTES=YES
  
  Note: a previous solution provided by APAR IT27221 is
  incomplete.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * AIX/LINUX                                                    *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to DB2 v11.1.4.6                                     *
  ****************************************************************
  

Problem conclusion

Temporary fix

Comments

APAR Information

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

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

Fix information

Applicable component levels