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https://issues.apache.org/jira/browse/IMPALA-8022?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-8022 started by Paul Rogers.
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> Add cardinality checks to PlannerTest
> -------------------------------------
>
> Key: IMPALA-8022
> URL: https://issues.apache.org/jira/browse/IMPALA-8022
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Affects Versions: Impala 3.1.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Priority: Minor
>
> IMPALA-8021 suggests that we add cardinality to the standard EXPLAIN output.
> When we do so, the cardinality will appear in the plans generated by
> {{PlannerTest}}. We could just ignore the numbers, as we do for other derived
> values. Or, we could use this opportunity to verify the expected
> cardinalities.
> The expected cardinality is a critical number when planning queries: we
> decide join planning based on that number (sometimes multiplied by row
> width.) To prevent regressions, we want to verify that we've not changed the
> cardinality estimates except by design.
> Since cardinality estimates may vary a bit, do a range-based comparison,
> accepting as valid any value within 5% of the expected value. (Except for
> zero, if zero is expected, the actual estimate must also be zero.)
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