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https://issues.apache.org/jira/browse/TRAFODION-2667?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on TRAFODION-2667 started by David Wayne Birdsall.
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> Incorrect UEC calculation
> -------------------------
>
> Key: TRAFODION-2667
> URL: https://issues.apache.org/jira/browse/TRAFODION-2667
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Environment: All
> Reporter: David Wayne Birdsall
> Assignee: David Wayne Birdsall
>
> When applying a predicate to histogram data for the same column, the
> resulting UECs are sometimes incorrect.
> ColStatDesc::applySel (optimizer/ColStatDesc.cpp) calls
> ColStatDesc::calculateCorrectResultUec to do this UEC calculation. The latter
> assumes that the predicate is on a column that is independent of the
> histogram column. In the case that the predicate is on the same column as the
> histogram, it is clearly quite dependent! Instead, the UEC should be reduced
> proportionately in the same manner as the row count.
> Though this is a simple change, the consequences may be far-reaching. Plan
> changes are likely. Adjustments to Optimizer tuning parameters are likely to
> be required. This change, then, should only be done in concert with a larger
> tuning effort.
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