PH22186: POOR PERFORMANCE FOR A QUERY CONTAINING AN EXPRESSION JOIN PREDICATE AND AN INDEX ON EXPRESSION INDEX IS NOT AVAILABLE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• For a query that contains a join predicate that is an expression
  with no supporting index on expression index,  we can choose to
  build a sparse index on this inner table. But this is a cost
  decision even though a better solution may not exist. Therefore,
  we should favor building a sparse index on the inner table in
  most cases.
  
  Additional keywords and symptoms.
  SQLPERFORMANCE SQLSPIDX SPARSEINDEX
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All Db2 12 for z/OS users who run queries                    *
  * with join predicates referencing column                      *
  * expressions.                                                 *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Db2 may choose a nested loop join with                       *
  * with an R scan or an index scan that                         *
  * does not cover the join predicates                           *
  * when the query contains join                                 *
  * predicates referencing column                                *
  * expressions. This can result                                 *
  * in sub-optimal performance.                                  *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply corrective PTF when available                          *
  ****************************************************************
  Db2 may choose a nested loop join with a R scan
  or an index scan that doesn't cover join predicates,
  when the query contains join predicates referencing
  column expressions.
  It can cause sub-optimal performance when the sort merge join
  is not eligible and only sparse index access is eligible.
  

Problem conclusion

• The performance problem described above is solved by PH22186 by
   detecting that neither the sort merge join nor the index plan
  is available to cover the join predicates referencing the
  column expression. When the above conditions are detected, the
   sparse index access will be favored.
  SQLWHERE SQLSPARSEINDEX SPARSEINDEX SQLPERFORMANCE
  

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:

  UI70861

Modules/Macros

• DSNXOCSC DSNXOPTH
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI70861

     UP20/08/11 P F008 ¢

Fix is available

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