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

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-24234?focusedWorklogId=496334&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-496334 ]

ASF GitHub Bot logged work on HIVE-24234:
-----------------------------------------

                Author: ASF GitHub Bot
            Created on: 07/Oct/20 06:39
            Start Date: 07/Oct/20 06:39
    Worklog Time Spent: 10m 
      Work Description: rbalamohan opened a new pull request #1560:
URL: https://github.com/apache/hive/pull/1560


   https://issues.apache.org/jira/browse/HIVE-24234
   
   Queries with grouping sets process input records multiple times and increases significantly the number hash aggregation lookup operations. When there is not significant reduction with aggregation, it becomes memory intensive and adds up to JVM mem pressure. 
   
   Earlier, due to minor bug, it wasn't switching over to hash mode. This has been fixed in the current patch and also takes care of the situation, when grouping sets are not very effective in reduction. 
   
   Tried out Q67 in TPCDS in internal cluster which shows significant improvement with this.
   
   For standalone tests, TestVectorGroupByOperator covers this.
   


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Issue Time Tracking
-------------------

            Worklog Id:     (was: 496334)
    Remaining Estimate: 0h
            Time Spent: 10m

> 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
>
>          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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