IBM Support

PK66755: IBM HTTP SERVER MOD_REWRITE MAP CAN RESULT IN HIGH CPU USAGE WHEN THOUSANDS OF STRINGS ARE PASSED AS KEYS

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APAR status

  • Closed as program error.

Error description

  • IHS 2.0.47 "RewriteMap lookups can use High CPU when thousands
    of strings are passed as keys to the map lookup
    

Local fix

  • We will provide an ifix (which for 2.0.47.1 is not be more than
    a zip
    file with a README and replacement mod_rewrite.so) that will
    have a
    prerequisite of latest 2.0.47.1 maintenance (PK65782).
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: mod_rewrite configurations which result in   *
    * thousands of strings passed in as keys to the map lookup     *
    ****************************************************************
    * PROBLEM DESCRIPTION: Performance of an in-memory cache can   *
    * degrade with large numbers of compared strings.              *
    ****************************************************************
    * RECOMMENDATION: Apply this fix if high CPU is encountered    *
    * when using rewrite maps.                                     *
    ****************************************************************
    mod_rewrite maintains an in-memory cache of comparisons against
    a rewrite map.  Due to the data structure used, performance can
    degrade as the number of entries in the cache increases.  High
    CPU can occur when there are thousands of elements.
    The number of elements in the cache is generally much larger
    than the number of entries in the rewrite map, since the set
    of unique request URLs can result in a large set of comparisons
    against the map.
    

Problem conclusion

  • The data structure used for the in-memory cache was changed to
    a hash table, greatly reducing the number of required string
    comparisons, thus resolving the high CPU when the cache
    contained thousands of entries.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PK66755

  • Reported component name

    IBM HTTP SERVER

  • Reported component ID

    5724J0801

  • Reported release

    60I

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2008-05-28

  • Closed date

    2008-06-25

  • Last modified date

    2008-06-25

  • 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

    IBM HTTP SERVER

  • Fixed component ID

    5724J0801

Applicable component levels

  • R60A PSN

       UP

  • R60H PSN

       UP

  • R60P PSN

       UP

  • R60I PSN

       UP

  • R60S PSN

       UP

  • R60W PSN

       UP

  • R60Z PSN

       UP

  • R61A PSN

       UP

  • R61H PSN

       UP

  • R61P PSN

       UP

  • R61I PSN

       UP

  • R61S PSN

       UP

  • R61W PSN

       UP

  • R61Z PSN

       UP

[{"Line of Business":{"code":"LOB45","label":"Automation"},"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Product":{"code":"SSEQTJ","label":"IBM HTTP Server"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"6.0"}]

Document Information

Modified date:
07 September 2022