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https://issues.apache.org/jira/browse/SPARK-33399?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17228664#comment-17228664
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Apache Spark commented on SPARK-33399:
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User 'prakharjain09' has created a pull request for this issue:
https://github.com/apache/spark/pull/30300
> Reduce unneeded exchanges after SortMerge joins
> -----------------------------------------------
>
> Key: SPARK-33399
> URL: https://issues.apache.org/jira/browse/SPARK-33399
> Project: Spark
> Issue Type: Task
> Components: SQL
> Affects Versions: 2.4.7, 3.0.0, 3.0.1
> Reporter: Prakhar Jain
> Priority: Major
>
> Spark introduces unneeded exchanges if there is a Project after Inner join.
> Example:
>
> {noformat}
> spark.range(10).repartition($"id").createTempView("t1")
> spark.range(20).repartition($"id").createTempView("t2")
> spark.range(30).repartition($"id").createTempView("t3")
> val planned = sql(
> """
> |SELECT t2id, t3.id as t3id
> |FROM (
> | SELECT t1.id as t1id, t2.id as t2id
> | FROM t1, t2
> | WHERE t1.id = t2.id
> |) t12, t3
> |WHERE t1id = t3.id
> """.stripMargin).queryExecution.executedPlan
> *(9) Project [t2id#1034L, id#1004L AS t3id#1035L]
> +- *(9) SortMergeJoin [t1id#1033L], [id#1004L], Inner
> :- *(6) Sort [t1id#1033L ASC NULLS FIRST], false, 0
> : +- Exchange hashpartitioning(t1id#1033L, 5), true, [id=#1343]
> <---------------
> : +- *(5) Project [id#996L AS t1id#1033L, id#1000L AS t2id#1034L]
> : +- *(5) SortMergeJoin [id#996L], [id#1000L], Inner
> : :- *(2) Sort [id#996L ASC NULLS FIRST], false, 0
> : : +- Exchange hashpartitioning(id#996L, 5), true, [id=#1329]
> : : +- *(1) Range (0, 10, step=1, splits=2)
> : +- *(4) Sort [id#1000L ASC NULLS FIRST], false, 0
> : +- Exchange hashpartitioning(id#1000L, 5), true, [id=#1335]
> : +- *(3) Range (0, 20, step=1, splits=2)
> +- *(8) Sort [id#1004L ASC NULLS FIRST], false, 0
> +- Exchange hashpartitioning(id#1004L, 5), true, [id=#1349]
> +- *(7) Range (0, 30, step=1, splits=2){noformat}
> The marked exchange in the above plan can be removed.
>
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