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Posted to dev@hive.apache.org by "Kevin Wilfong (JIRA)" <ji...@apache.org> on 2013/01/02 21:34:13 UTC
[jira] [Updated] (HIVE-3552) HIVE-3552 performant manner for
performing cubes/rollups/grouping sets for a high number of grouping set
keys
[ https://issues.apache.org/jira/browse/HIVE-3552?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Kevin Wilfong updated HIVE-3552:
--------------------------------
Status: Open (was: Patch Available)
> 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.3552.10.patch, hive.3552.11.patch, hive.3552.1.patch, hive.3552.2.patch, hive.3552.3.patch, hive.3552.4.patch, hive.3552.5.patch, hive.3552.6.patch, hive.3552.7.patch, hive.3552.8.patch, hive.3552.9.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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