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https://issues.apache.org/jira/browse/SPARK-21509?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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jin xing closed SPARK-21509.
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Resolution: Won't Fix
> Add a config to enable adaptive query execution only for the last query
> execution.
> -----------------------------------------------------------------------------------
>
> Key: SPARK-21509
> URL: https://issues.apache.org/jira/browse/SPARK-21509
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.2.0
> Reporter: jin xing
>
> Feature of adaptive query execution is a good way to avoid generating too
> many small files on HDFS, like mentioned in SPARK-16188.
> When feature of adaptive query execution is enabled, all shuffles will be
> coordinated. The drawbacks:
> 1. It's hard to balance the num of reducers(this decides the processing
> speed) and file size on HDFS
> 2. It generates some unnecessary
> shuffles(https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala#L101)
> 3. It generates lots of jobs, which have extra cost for scheduling.
> We can add a config and enable adaptive query execution only for the last
> shuffle.
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