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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Jul 24, 2019

RELATED IDEAS

Better filter factors - use RI for this

The Db2/LUW optimizer has some algorithms that affect the optimization of queries on that platform based on the fact that RI is involved.  But, Db2 for Z can calculate very incorrect filter factors that can be much more correct if Db2 enforced RI were taken into account.  I believe (but I am not sure) that you can actually register a "application enforced RI" into the Db2/LUW catalog and that also is then taken into account by the optimizer (and while I like this, it would ever go further than what I am initially asking for).

Incorrect filter factor estimation does lead to bad optimization.

Basically, I would like for Db2 to get the estimated filter factors as correct as possible.  And, if reviewing the known RI relationships can to this, it would really help.

Right now, our workaround is to hint queries that have bad optimization due to factors like this.

(note that I had a PMR interaction on this.  It is PMR 70301,122,000). 

Needed by Date Dec 31, 2020
  • Admin
    Janet Figone
    Reply
    |     Dec 3, 2020

    Larry, Thank you for submitting this product enhancement request to the Db2 for z/OS development team. We have reviewed it and determined that, while the solution of using RI for improving filter factor estimation is understood - we plan to address misestimation of optimizer costing in a more general manner.

    Please continue to submit your enhancement ideas to us for review and consideration in a future release.

    Sincerely,

    The Db2 for z/OS Development team

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