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IT36781: OPTIMIZER IS CHOOSING SEQUENTIAL SCAN WITHIN QUERY PLAN OF 9 TABLE JOIN USING INNER AND LEFT OUTER JOINS

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APAR status

  • Closed as Permanent restriction.

Error description

  • After upgrading to 12.10.FC14 from a 11.70.FC8 special build,
    customer observed a query was taking minutes
    to run when it used to run in under a second.
    
    The query is a 9 table join with 6 inner joins and 3 left outer
    joins.
    
    In the bad query plan, the optimizer is choosing a sequential
    scan on a larger table earlier in the
    plan and it becomes the basis for most of the time cost.
    
    Using an ORDERED join for this particular query provides a hint
    for optimizer to choose a path like the
    faster 11.70 plan.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * After upgrading to 12.10.FC14 from a 11.70.FC8 special build *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * optimizer is choosing sequential scan within query plan of 9 *
    * table join using inner and left outer joins                  *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    

Problem conclusion

  • the customer seems to be happy with the workaround and if they
    decide to move to a higher server version than 12.10.xC14 they
    can try removing the workaround and see how the query performs.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT36781

  • Reported component name

    INFORMIX SERVER

  • Reported component ID

    5725A3900

  • Reported release

    C10

  • Status

    CLOSED PRS

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2021-05-04

  • Closed date

    2023-02-02

  • Last modified date

    2023-02-02

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

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

Fix information

Applicable component levels

[{"Business Unit":{"code":"BU053","label":"Cloud \u0026 Data Platform"},"Product":{"code":"SSGU8G","label":"Informix Servers"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"C10"}]

Document Information

Modified date:
02 February 2023