[GitHub] [spark] wangyum commented on pull request #29120: [SPARK-32291][SQL] COALESCE should not reduce the child parallelism if it contains a Join

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wangyum commented on pull request #29120:
URL: https://github.com/apache/spark/pull/29120#issuecomment-846507897


   This change will introduce an additional shuffle. We can use `localCheckpoint` to workaround this issue:
   ```scala
   spark.range(100).createTempView("t1")
   spark.range(200).createTempView("t2")
   spark.sql("set spark.sql.autoBroadcastJoinThreshold=0")
   spark.sql("select t1.* from t1 join t2 on (t1.id = t2.id)").localCheckpoint().coalesce(1).show()
   ```


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