PI71368: R-SCAN ACCESS PATH CHOSEN OVER MULTI-INDEX ACCESS FOR A TABLE WHICH QUALIFIES FOR NPGTHRSH BEHAVIOR

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• R-scan access path chosen over multi-index access for a table
  which qualifies for NPGTHRSH behavior.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All DB2 for z/OS users of VOLATILE tables or the NPGTHRSH    *
  * zparm.                                                       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * For a table defined with the VOLATILE                        *
  * attribute, or a table that qualifies                         *
  * for NPGTHRSH rules, the DB2 Optimizer                        *
  * may sometimes choose a table space                           *
  * scan or non-matching index scan rather                       *
  * than matching index access that uses                         *
  * multiple index ORing, when multiple                          *
  * index ORing is the only matching index                       *
  * access available.                                            *
  *                                                              *
  * This can occur when the matching                             *
  * predicates used for index ORing                              *
  * are estimated to not provide                                 *
  * sufficient filtering of the table.                           *
  *                                                              *
  * Filtering estimates, however, for                            *
  * tables defined as VOLATILE or tables                         *
  * that qualify for NPGTHRSH rules should                       *
  * not be used to disable matching index                        *
  * access through a multi-index access                          *
  * path, because those estimates may not                        *
  * be accurate.                                                 *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The DB2 Optimizer may choose a table space scan over matching
  
  index access involving index OR'ing, for tables that have the
  
  VOLATILE attribute, or tables that qualify for NPGTHRSH rules.
  
  
  
  This can occur when the matching predicates used in the index
  
  OR'ing plan are estimated to provide insufficient filtering of
  
  the table.
  
  
  
  This can result in a table space scan or non-matching
  
  index scan being done instead of doing matching index access
  
  by OR'ing multiple indexes.
  

Problem conclusion

• The rules for VOLATILE tables and NPGTHRSH tables are changed
  
  to allow matching index access involving index ORing to be
  
  selected over table space scan and non-matching index scan
  
  regardless of the estimated filtering of the matching
  
  predicates.
  
  
  
  Matching single index access is preferred over matching index
  
  ORing access regardless of how many matching predicates are
  
  involved in the competing plans.
  
  
  
  Additional Keywords:
  
  SQLACCESSPATH SQLPERFORMANCE SQLOR MIDX
  

Temporary fix

Comments

APAR Information

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

  PI71365

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

  UI44411

Modules/Macros

• DSNXOCSC DSNXOGCM
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI44411

     UP17/02/21 P F702

Fix is available

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