pan3793 commented on code in PR #56961:
URL: https://github.com/apache/spark/pull/56961#discussion_r3531245122
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sql/core/src/main/scala/org/apache/spark/sql/execution/basicPhysicalOperators.scala:
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@@ -938,6 +945,24 @@ case class UnionExec(children: Seq[SparkPlan]) extends
SparkPlan with CodegenSup
// Take the output attributes of this union and map the partitioner to
them.
val attributeMap = children.head.output.zip(output).toMap
partitioner match {
+ case headKp: KeyedPartitioning =>
+ // A `UnionExec` concatenates its children's partitions in order
(one child's
+ // partitions after another's), so the merged `KeyedPartitioning`
carries the
+ // concatenation of the children's partition keys, one key per
physical output
+ // partition. Children usually hold different key sets, so the
merged keys often
+ // contain duplicates and `isGrouped` is false; a downstream
`GroupPartitionsExec`
+ // regroups partitions that share a key. The children's
expressions have already
+ // been remapped to the first child's attributes by
`prepareOutputPartitioning`;
+ // here they are remapped to the union's output attributes.
+ val mergedKeys = partitionings.flatMap {
+ case k: KeyedPartitioning => k.partitionKeys
+ case _ => return super.outputPartitioning
+ }
+ val mergedExpressions = headKp.expressions.map(_.transform {
+ case a: Attribute if attributeMap.contains(a) => attributeMap(a)
+ })
+ val isGrouped = mergedKeys.distinct.size == mergedKeys.size
+ KeyedPartitioning(mergedExpressions, mergedKeys, isGrouped)
Review Comment:
@peter-toth, thank you for pointing out this correctness issue, applied this
fix.
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