[jira] [Assigned] (HIVE-24234) Improve checkHashModeEfficiency in VectorGroupByOperator

["Rajesh Balamohan (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-24234?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rajesh Balamohan reassigned HIVE-24234:
---------------------------------------

    Assignee: Rajesh Balamohan

> Improve checkHashModeEfficiency in VectorGroupByOperator
> --------------------------------------------------------
>
>                 Key: HIVE-24234
>                 URL: https://issues.apache.org/jira/browse/HIVE-24234
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Rajesh Balamohan
>            Assignee: Rajesh Balamohan
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HIVE-24234.wip.patch
>
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> 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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