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https://issues.apache.org/jira/browse/SPARK-18631?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15706495#comment-15706495
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Apache Spark commented on SPARK-18631:
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User 'markhamstra' has created a pull request for this issue:
https://github.com/apache/spark/pull/16065
> Avoid making data skew worse in ExchangeCoordinator
> ---------------------------------------------------
>
> Key: SPARK-18631
> URL: https://issues.apache.org/jira/browse/SPARK-18631
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.3, 2.0.2, 2.1.0
> Reporter: Mark Hamstra
> Assignee: Mark Hamstra
>
> The logic to resize partitions in the ExchangeCoordinator is to not start a
> new partition until the targetPostShuffleInputSize is equalled or exceeded.
> This can make data skew problems worse since a number of small partitions can
> first be combined as long as the combined size remains smaller than the
> targetPostShuffleInputSize, and then a large, data-skewed partition can be
> further combined, making it even bigger than it already was.
> It's a fairly simple to change the logic to create a new partition if adding
> a new piece would exceed the targetPostShuffleInputSize instead of only
> creating a new partition after the targetPostShuffleInputSize has already
> been exceeded. This results in a few more partitions being created by the
> ExchangeCoordinator, but data skew problems are at least not made worse even
> though they are not made any better.
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