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https://issues.apache.org/jira/browse/SPARK-16052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15362750#comment-15362750
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Dongjoon Hyun commented on SPARK-16052:
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Hi, [~yhuai].
Could you review this PR when you have some time?
> Improve `CollapseRepartition` optimizer for Repartition/RepartitionBy
> ---------------------------------------------------------------------
>
> Key: SPARK-16052
> URL: https://issues.apache.org/jira/browse/SPARK-16052
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Dongjoon Hyun
>
> This issue improves `CollapseRepartition` to optimize the adjacent
> combinations of **Repartition** and **RepartitionBy**. Also, this issue adds
> a testsuite for this optimizer.
> **Before**
> {code}
> scala> spark.range(10).repartition(1, $"id").repartition(1, $"id").explain
> == Physical Plan ==
> Exchange hashpartitioning(id#0L, 1)
> +- Exchange hashpartitioning(id#0L, 1)
> +- *Range (0, 10, splits=8)
> scala> spark.range(10).repartition(1, $"id").repartition($"id").explain
> == Physical Plan ==
> Exchange hashpartitioning(id#6L, 200)
> +- Exchange hashpartitioning(id#6L, 1)
> +- *Range (0, 10, splits=8)
> {code}
> **After**
> {code}
> scala> spark.range(10).repartition(1, $"id").repartition(1, $"id").explain
> == Physical Plan ==
> Exchange hashpartitioning(id#0L, 1)
> +- *Range (0, 10, splits=8)
> scala> spark.range(10).repartition(1, $"id").repartition($"id").explain
> == Physical Plan ==
> Exchange hashpartitioning(id#6L, 200)
> +- *Range (0, 10, splits=8)
> {code}
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