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Status Future consideration
Workspace Db2
Created by Guest
Created on Mar 22, 2023

Optimizer does not use HIGH2KEY/LOW2KEY for columns with COLCARD 1

Optimization issue if a business_time_oriented table  has only one row. In syscat.columns the content of the business_time columns are detected (high2key, low2key) but the value can not be found in the distribution statistics. This leads default filter factors (1/3) of the to business time predicates and in sum to a way too small filter factor.  This leads to a MSJOIN with a low filtering join-predicate (which we don't like eather. The statistics would be needed to be brought into syscoldist? Omiting sampling was not successful.

This single row table was not the the main source of the cardinality under-estimation error in the original query they provided.

The issue here is that the optimizer does not use HIGH2KEY/LOW2KEY for columns with COLCARD 1.

This is a known issue and certainly something that needs to be be improved,

Needed By Quarter
  • Admin
    Ned Whelan
    Jun 20, 2023

    Thank you for submitting this Idea! We have reviewed the ticket and will consider it for a future release. Please continue to monitor and vote on it.