[jira] [Commented] (HIVE-3552) HIVE-3552 performant manner for performing cubes/rollups/grouping sets for a high number of grouping set keys

["Namit Jain (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-3552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13508575#comment-13508575 ] 

Namit Jain commented on HIVE-3552:
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tests passed
                
> HIVE-3552 performant manner for performing cubes/rollups/grouping sets for a high number of grouping set keys
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: HIVE-3552
>                 URL: https://issues.apache.org/jira/browse/HIVE-3552
>             Project: Hive
>          Issue Type: New Feature
>          Components: Query Processor
>            Reporter: Namit Jain
>            Assignee: Namit Jain
>         Attachments: hive.3552.1.patch
>
>
> This is a follow up for HIVE-3433.
> Had a offline discussion with Sambavi - she pointed out a scenario where the
> implementation in HIVE-3433 will not scale. Assume that the user is performing
> a cube on many columns, say '8' columns. So, each row would generate 256 rows
> for the hash table, which may kill the current group by implementation.
> A better implementation would be to add an additional mr job - in the first 
> mr job perform the group by assuming there was no cube. Add another mr job, where
> you would perform the cube. The assumption is that the group by would have 
> decreased the output data significantly, and the rows would appear in the order of
> grouping keys which has a higher probability of hitting the hash table.

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