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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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Description: 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.
> 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: 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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