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Posted to issues@hive.apache.org by "Simhadri G (Jira)" <ji...@apache.org> on 2022/03/07 09:47:00 UTC

[jira] [Assigned] (HIVE-26009) Determine number of buckets for implicitly bucketed ACIDv2 tables

     [ https://issues.apache.org/jira/browse/HIVE-26009?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Simhadri G reassigned HIVE-26009:
---------------------------------


> Determine number of buckets for implicitly bucketed ACIDv2 tables 
> ------------------------------------------------------------------
>
>                 Key: HIVE-26009
>                 URL: https://issues.apache.org/jira/browse/HIVE-26009
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Simhadri G
>            Assignee: Simhadri G
>            Priority: Major
>
> Hive tries to set number of reducers equal to number of buckets here: 
> [https://github.com/apache/hive/blob/9857c4e584384f7b0a49c34bc2bdf876c2ea1503/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java#L6958] 
>  
> The numberOfBuckets for implicitly bucketed tables is set to -1 by default. When this is the case, it is left to hive to estimate the number of reducers required the job, based on job input, and configuration parameters.
> [https://github.com/apache/hive/blob/9857c4e584384f7b0a49c34bc2bdf876c2ea1503/ql/src/java/org/apache/hadoop/hive/ql/exec/Utilities.java#L3369]
>  
> This estimate is not optimal in all cases. In the worst case, it case result in a single reducer being launched , which can lead to a significant bottleneck in performance .
>  
> Ideally,  the number of reducers launched should equal to number of buckets, which is the case for explicitly bucketed tables.
>  
>  



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