jin xing created SPARK-21509:
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Summary: 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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