IBM Support

IT27216: PERFORMANCE REGRESSION IN BLU QUERIES CONTAINING JOIN ON VARCHARCOLUMNS ON AIX

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APAR status

  • Closed as program error.

Error description

  • A performance degradation in Db2 V11.1 M4FP4 can be observed
    when joining VARCHAR columns in BLU queries on AIX.
    Compared Db2 V11.1 M4FP4 to Db2 V11.1 M3FP3, the degradation
    reduced query performance up to 20-30%.
    
    If you analysis such queries using tprof, you can find
    ibm_cde::services::ManagedStringBase::assign very close to the
    top.
    
    A sample tprof output of a query affected by this issue:
    
    ...
      Total Ticks For All Processes
    (/db2/m3_1109/lib64/libdb2blu.a[shr_64.o]) = 18097
    
    Subroutine                 Ticks    %   Source
    Address  Bytes
    ==========                 ===== ====== ======
    =======  =====
    .ibm_cde::query::ConcatEvaluator::computeListOfNotCodeableInputs
    (bool&,ibm_cde::types::BitString&,ibm_cde::query::WorkUnit&)
    2561   9.82 ConcatEvaluator.cpp   4c80848   3520
    .ibm_cde::services::ManagedStringBase::assign(const unsigned
    char*,const unsigned long)   1791   6.87
    ColumnDictionaryVersionBase.cpp  1125638    200
    .ibm_cde::types::VarLenString::initCompareFunc()    941   3.61
    VarLenString.cpp       bbceb8    2b0
    .ibm_cde::types::VarLenString::formString(const
    char*,ibm_cde::types::DataType,unsigned short)    923   3.54
    ColumnDictionaryVersionBase.cpp  110a4a8    2d0
    .ibm_cde::data::ColumnDictionaryVersion<ibm_cde::types::VarLenSt
    ring>::decode(ibm_cde::data::QCode,ibm_cde::types::ValUncoded&)
    const    895   3.43 ColumnDictionaryVersionBase.cpp  1168908
    360
    ...
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * ALL                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Db2 11.1 Mod 4 Fixpack 5 or higher                *
    ****************************************************************
    

Problem conclusion

  • First fixed in Db2 11.1 Mod 4 Fixpack 5
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT27216

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2018-12-05

  • Closed date

    2020-01-16

  • Last modified date

    2020-01-16

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

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

Fix information

  • Fixed component name

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

  • RB10 PSN

       UP

[{"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSEPGG","label":"Db2 for Linux, UNIX and Windows"},"Component":"","ARM Category":[],"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1","Edition":"","Line of Business":{"code":"LOB10","label":"Data and AI"}}]

Document Information

Modified date:
16 January 2020