PI26148: INCORRECT OUTPUT (LESS ROW FOUND) FOR QUERY THAT USES REVERSE INDEX SCAN WITH INDEX SKIPPING

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Incorrect output - less row found with query that uses
  reverse index scan with index skipping
  
  Those cases can be identified via two explain tables.
  PLAN_TABLE.SCAN_DIRECTION=R;
  DSN_DETCOST_TABBLE.IXSCAN_SKIP_DUPS=Y
  

Local fix

• 1/ use un-compressed tables.
  
  Note:  The problem is not related to compression.  The access
  path is index only and compression is not involved.  The process
  of decompressing the table space resulted in changing the access
  path from using index skipping + reverse index scan to using
  forward index scan.
  
  2/ re-write query, so it does not use reverse index scan + index
  skipping
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All DB2 11 for z/OS users doing              *
  *                 reverse index scans on partitioned           *
  *                 indexes.                                     *
  ****************************************************************
  * PROBLEM DESCRIPTION: Incorrect output - less rows found      *
  *                      with a query that uses reverse index    *
  *                      scan on partitioned indexes.            *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When scanning in the reverse direction within a partitioned
  index and at the same time skipping non-distinct values, valid
  index keys could be missed.
  
    Additional keywords: DB2INCORR/K, INCORROUT, SQLINCORR,
                         SQLINCORROUT
  

Problem conclusion

• Code within DB2 has been modified to correctly begin scanning
  within the next previous partition for qualifying keys, when
  index key skipping is active.
  

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:

  UI22940

Modules/Macros

•    DSNKFPRV
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RB10 PSY UI22940

     UP14/11/27 P F411 Ž

Fix is available

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