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https://issues.apache.org/jira/browse/HIVE-908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12791455#action_12791455
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Namit Jain commented on HIVE-908:
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Based on an offline discussion, this is a very important feature for our users.
> optimize limit
> --------------
>
> Key: HIVE-908
> URL: https://issues.apache.org/jira/browse/HIVE-908
> Project: Hadoop Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Namit Jain
> Fix For: 0.5.0
>
>
> If there is a limit, all the mappers have to finish and create 'limit' number
> of rows - this can be pretty expensive for a large file.
> The following optimizations can be performed in this area:
> 1. Start fewer mappers if there is a limit - before submitting a job, the
> compiler knows that there is a limit - so, it might be useful to increase the
> split size, thereby reducing the number of mappers.
> 2. A counter is maintained for the total outputs rows - the mappers can look
> at those counters and decide to exit instead of emitting 'limit' number of
> rows themselves.
> 2. may lead to some bugs because of bugs in counters, but 1. should
> definitely help
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