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https://issues.apache.org/jira/browse/HIVE-9931?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gopal V updated HIVE-9931:
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Labels: ORC (was: )
> Approximate nDV statistics from ORC bloom filter population
> -----------------------------------------------------------
>
> Key: HIVE-9931
> URL: https://issues.apache.org/jira/browse/HIVE-9931
> Project: Hive
> Issue Type: Improvement
> Components: Statistics
> Affects Versions: 1.2.0
> Reporter: Gopal V
> Labels: ORC
>
> The current CBO implementation requires column nDV statistics to produce good
> estimates of JOIN selectivity and filter selectivity.
> The ORC bloom filters provides an opportunity to estimate the net population
> of a row-group with false-positive rates capped for each row-group.
> This is not useful for filter conditions or join conditions with a
> cardinality which is a large fraction of the row-count, but can collect
> viable statistics for low-cardinality filter columns (de-normalization
> scenarios) or for JOIN dimension columns of low cardinality (demographics or
> store location).
> The challenge in this feature is in distinguishing between these two
> scenarios, not in the derivation of the approximate nDV itself.
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