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IT27744: IF COLUMNAR FUNCTIONALITY IS USED ON A SYSTEM WITH INTEL CPU THAT SUPPORTS AVX-512 THEN WRONG RESULTS ARE POSSIBLE

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APAR status

  • Closed as program error.

Error description

  • SQL queries against Columnar tables on systems with Intel CPU
    supporting AVX-512 could return incorrect results.
    
    Please, review  /proc/cpuinfo to determine if CPU is indeed
    AVX-512, or review db2diag.log.
    
    Example of db2diag.log entry showing AVX512 in the list of CPU
    features:
    
    2019-01-10-09.18.12.106183-480 I1E1835               LEVEL:
    Event
    PID     : 411800               TID : 139987704543104 PROC :
    db2set
    INSTANCE: xxx             NODE : 000
    HOSTNAME: xxx
    FUNCTION: DB2 UDB, RAS/PD component, pdLogInternal, probe:120
    START   : New Diagnostic Log file
    DATA #1 : Build Level, 248 bytes
    Instance "xxx" uses "64" bits and DB2 code release "xxx"
    with level identifier "020A010F".
    Informational tokens are xxx
    DATA #2 : System Info, 664 bytes
    System: Linux xxx 10 3 x86_64
    CPU: total:96 online:96 Cores per socket:24 Threading degree per
    core:2 SIMD:Y CPU Features:SSE2,SSSE3,SSE4,AVX2,AVX512
    CPU binding: not in use
    Physical Memory(MB): total:63909 free:50226
    Virtual  Memory(MB): total:95973 free:82290
    Swap     Memory(MB): total:32064 free:32064
    ..
    
    Example of wrong result:
    
    db2 "SELECT d_moy FROM date_dim WHERE d_moy =1"
    
    could return values other then 1.
    

Local fix

  • db2set DB2_CPU_FEATURE_DISABLE=AVX512
    Instance restart is needed.
    Once this workaround is in place , AVX512 will dissapear from
    the list of CPU Features in new db2diag.log entries.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * Columnar Tables only                                         *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * Please, See Error Description and install this fix.          *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Please, See Error Description and install this fix.          *
    ****************************************************************
    

Problem conclusion

  • Please, See Error Description and install this fix.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT27744

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2019-01-11

  • Closed date

    2021-11-05

  • Last modified date

    2021-11-05

  • 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 PSY

       UP

[{"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSEPGG","label":"DB2 for Linux- UNIX and Windows"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1","Line of Business":{"code":"LOB10","label":"Data and AI"}}]

Document Information

Modified date:
03 May 2022