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https://issues.apache.org/jira/browse/HIVE-17935?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16234652#comment-16234652
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Andrew Sherman commented on HIVE-17935:
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Thanks [~prasanth_j] for helpful comments. Do you think the possible
performance regression for some jobs to be large? Is it fair to say that the
gains from changing the default are potentially large while the losses are
comparatively small?
> Turn on hive.optimize.sort.dynamic.partition by default
> -------------------------------------------------------
>
> Key: HIVE-17935
> URL: https://issues.apache.org/jira/browse/HIVE-17935
> Project: Hive
> Issue Type: Bug
> Reporter: Andrew Sherman
> Assignee: Andrew Sherman
> Priority: Major
> Attachments: HIVE-17935.1.patch, HIVE-17935.2.patch
>
>
> The config option hive.optimize.sort.dynamic.partition is an optimization for
> Hive’s dynamic partitioning feature. It was originally implemented in
> [HIVE-6455|https://issues.apache.org/jira/browse/HIVE-6455]. With this
> optimization, the dynamic partition columns and bucketing columns (in case of
> bucketed tables) are sorted before being fed to the reducers. Since the
> partitioning and bucketing columns are sorted, each reducer can keep only one
> record writer open at any time thereby reducing the memory pressure on the
> reducers. There were some early problems with this optimization and it was
> disabled by default in HiveConf in
> [HIVE-8151|https://issues.apache.org/jira/browse/HIVE-8151]. Since then
> setting hive.optimize.sort.dynamic.partition=true has been used to solve
> problems where dynamic partitioning produces with (1) too many small files on
> HDFS, which is bad for the cluster and can increase overhead for future Hive
> queries over those partitions, and (2) OOM issues in the map tasks because it
> trying to simultaneously write to 100 different files.
> It now seems that the feature is probably mature enough that it can be
> enabled by default.
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