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PI43645: INCORRECT COMPOUND FILTER FACTOR FOR A GROUP OF PREDICATES CONTAINING AN IN LIST

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APAR status

  • Closed as program error.

Error description

  • DB2 generates an incorrect compound filter factor in IMFF for a
query with an IN list predicate despite having multi cardinality
and multi frequency entries in SYSCOLDIST.










Keywords:
SQLPERFORMANCE
SQLACCESSPATH
FILTERFACTOR

Local fix

  • N/A

Problem summary

  • ****************************************************************
* USERS AFFECTED: DB2 for z/OS users collecting multi-column   *
*                 frequencies or multi-column histograms.      *
****************************************************************
* PROBLEM DESCRIPTION: DB2 may compute an incorrect filter     *
*                      factor for a set of predicates          *
*                      containing an IN list predicate if      *
*                      multi-column frequency or multi-column  *
*                      histogram statistics exist.             *
****************************************************************
* RECOMMENDATION:                                              *
****************************************************************
DB2 may compute an inaccurate compound filter factor.  This
problem can occur if all of the following conditions are
met.

  * An IN list predicate is coded in the query.

  * Additional predicates are coded against the same
    table as the IN list predicate.

  * Multi-column frequency or multi-column histogram
    statistics exist for all or some of the columns
    referenced by the predicates against the table.

This problem can result in selection of an inefficient
access path leading to poor query performance.

Additional Keywords:
SQLPERFORMANCE SQLACCESSPATH SQLSTATS SQLIN

Problem conclusion

  • DB2 code has been corrected to accurately estimate the compound
filter factor in the described scenario.

Temporary fix

  • 



Comments


    

  • 



APAR Information




    

  • APAR number
    PI43645
    • 

  • Reported component name
    DB2 OS/390 & Z/
    • 

  • Reported component ID
    5740XYR00
    • 

  • Reported release
    A10
    • 

  • Status
    CLOSED  PER
    • 

  • PE
    NoPE
    • 

  • HIPER
    NoHIPER
    • 

  • Special Attention
    NoSpecatt
    • 

  • Submitted date
    2015-06-24
    • 

  • Closed date
    2015-11-12
    • 

  • Last modified date
    2015-12-02
    • 





    

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

    • 

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

    
UI32905 UI32906
    

    • 



Modules/Macros


    

  • DSNXOGNC

    



Fix information


    

  • Fixed component name
    DB2 OS/390 & Z/
    • 

  • Fixed component ID
    5740XYR00
    • 



Applicable component levels


    

  • RA10  PSY  UI32905
       UP15/12/01  P  F511
    • 

  • RB10  PSY  UI32906
       UP15/12/01  P  F511
    • 



Fix is available


    

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Document Information


            

            


                        

            Modified date:
            

            02 December 2015
            

            
                      

        


        

        


      

    

  



    

  

  
    
            

          
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