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https://issues.apache.org/jira/browse/HIVE-4435?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Shreepadma Venugopalan updated HIVE-4435:
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Attachment: chart_1(1).png
> Column stats: Distinct value estimator should use hash functions that are
> pairwise independent
> ----------------------------------------------------------------------------------------------
>
> Key: HIVE-4435
> URL: https://issues.apache.org/jira/browse/HIVE-4435
> Project: Hive
> Issue Type: Bug
> Components: Statistics
> Affects Versions: 0.10.0
> Reporter: Shreepadma Venugopalan
> Assignee: Shreepadma Venugopalan
> Attachments: chart_1(1).png, HIVE-4435.1.patch
>
>
> The current implementation of Flajolet-Martin estimator to estimate the
> number of distinct values doesn't use hash functions that are pairwise
> independent. This is problematic because the input values don't distribute
> uniformly. When run on large TPC-H data sets, this leads to a huge
> discrepancy for primary key columns. Primary key columns are typically a
> monotonically increasing sequence.
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