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https://issues.apache.org/jira/browse/HIVE-26009?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Simhadri G reassigned HIVE-26009:
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> 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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