IC88998: AUTO READAHEAD IS NOT PERFORMING INDEX-DATA READ AHEAD WITH OLD-STYLE ATTACHED INDEXES WHICH CAN LEAD TO A PERFORMANCE PROBLEM

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APAR status

  • Closed as program error.

Error description

  • With the introduction of AUTO Readahead we are not seeing
    index-data read ahead occur.  This is causing a performance
    problem and we see a lot of IO Waits for the sqlexec threads
    that are having issues.
    
    This occurs when the table uses attached indexes (old style).
    If the table has detached indexes, you will see index-data
    readahead occur.
    It's important to specify here, we are referring to "attached
    indexes" where the index data exists within the same partition
    as the data pages.
    
    In later versions of the product "attached indexes" have also
    come to be known as indexes that are in the same dbspace as the
    data, but in a different partition.
    
    Attached Indexes:
    
    Partition ReadAhead Statistics
    
              Buffer    Disk    Hit  Data          Index
    Idx/Dat
    Partnum    Reads    Reads    Ratio # Reqs  Eff  # Reqs  Eff  #
    Reqs  Eff
    0x100181  150      2        98    0      0    1      0    0
    0
    0x1001f4  11829987  222003  98    0      0    1183    99    0
    0
    
    Detached Indexes:
    
    Partition ReadAhead Statistics
    
              Buffer    Disk    Hit  Data          Index
    Idx/Dat
    Partnum    Reads    Reads    Ratio # Reqs  Eff  # Reqs  Eff  #
    Reqs  Eff
    0x100148  150      6        96    0      0    1      0    0
    0
    0x100172  5789133  215078  96    0      0    1146    99    12292
    95
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * Users querying large tables that contain old-style attached  *
    * indexes                                                      *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Update to IDS-11.70.xC8                                      *
    ****************************************************************
    

Problem conclusion

  • Problem Fixed In IDS-11.70.xC8
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC88998

  • Reported component name

    INFORMIX SERVER

  • Reported component ID

    5725A3900

  • Reported release

    B70

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-12-10

  • Closed date

    2014-02-26

  • Last modified date

    2014-02-26

  • 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

    INFORMIX SERVER

  • Fixed component ID

    5725A3900

Applicable component levels

  • RB70 PSN

       UP

  • RB70 PSY

       UP



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Document information


More support for:

Informix Servers

Software version:

B70

Reference #:

IC88998

Modified date:

2014-02-26

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