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https://issues.apache.org/jira/browse/HIVE-15682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15855125#comment-15855125
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Xuefu Zhang commented on HIVE-15682:
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I took a look at the code block again, and it doesn't appear that per-row based
dummy iterator has much performance penalty. Nevertheless, we can create a
single dummy iterator and reuse it to avoid object creation (and gc). Other
than this, the whole code path doesn't seem having much room to optimize
> Eliminate the dummy iterator and optimize the per row based reducer-side
> processing
> -----------------------------------------------------------------------------------
>
> Key: HIVE-15682
> URL: https://issues.apache.org/jira/browse/HIVE-15682
> Project: Hive
> Issue Type: Improvement
> Components: Spark
> Affects Versions: 2.2.0
> Reporter: Xuefu Zhang
> Assignee: Xuefu Zhang
>
> HIVE-15580 introduced a dummy iterator per input row which can be eliminated.
> This is because {{SparkReduceRecordHandler}} is able to handle single key
> value pairs. We can refactor this part of code 1. to remove the need for a
> iterator and 2. to optimize the code path for per (key, value) based (instead
> of (key, value iterator)) processing. It would be also great if we can
> measure the performance after the optimizations and compare to performance
> prior to HIVE-15580.
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