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https://issues.apache.org/jira/browse/HIVE-24234?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rajesh Balamohan updated HIVE-24234:
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Attachment: HIVE-24234.wip.patch
> Improve checkHashModeEfficiency in VectorGroupByOperator
> --------------------------------------------------------
>
> Key: HIVE-24234
> URL: https://issues.apache.org/jira/browse/HIVE-24234
> Project: Hive
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
> Priority: Major
> Attachments: HIVE-24234.wip.patch
>
>
> Currently, {{VectorGroupByOperator::checkHashModeEfficiency}} compares the
> number of entries with the number input records that have been processed. For
> grouping sets, it accounts for grouping set length as well.
> Issue is that, the condition becomes invalid after processing large number of
> input records. This prevents the system from switching over to streaming
> mode.
> e.g Assume 500,000 input records processed, with 9 grouping sets, with
> 100,000 entries in hashtable. Hashtable would never cross 4,500,0000 entries
> as the max size itself is 1M by default.
> It would be good to compare the input records (adjusted for grouping sets)
> with number of output records (along with size of hashtable size) to
> determine hashing or streaming mode.
> E.g Q67.
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