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https://issues.apache.org/jira/browse/IMPALA-9972?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Quanlong Huang updated IMPALA-9972:
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Fix Version/s: (was: Impala 4.0)
> Use defined referential constraints for join cardinality calculations
> ---------------------------------------------------------------------
>
> Key: IMPALA-9972
> URL: https://issues.apache.org/jira/browse/IMPALA-9972
> Project: IMPALA
> Issue Type: Sub-task
> Components: Frontend
> Reporter: Shant Hovsepian
> Assignee: Shant Hovsepian
> Priority: Major
>
> Currently an estimation technique is used to determine if the join predicates
> consistent a foreign key -> primary key type of functional dependency. These
> types of joins are common in "star schemas" and allow for certain query
> planning optimization.
> The current technique however can produce both false negatives and false
> positives given the reliance on table stats which can be out of date or
> incorrect due to the statistical methods used to derive stats. For example
> higher variability in the error rates of the HyperLogLog algorithm used by
> stats computation to calculate the number of distinct values for a specific
> column.
> In case swhere a referential integrity constraint exists and is defined in
> the table metadata, this information should be used instead of the stats
> based estimation to determine the type and cardinality of a join.
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