Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/5208#discussion_r28394813
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/Exchange.scala ---
@@ -19,24 +19,39 @@ package org.apache.spark.sql.execution
import org.apache.spark.annotation.DeveloperApi
import org.apache.spark.shuffle.sort.SortShuffleManager
-import org.apache.spark.sql.catalyst.expressions
import org.apache.spark.{SparkEnv, HashPartitioner, RangePartitioner,
SparkConf}
import org.apache.spark.rdd.{RDD, ShuffledRDD}
import org.apache.spark.sql.{SQLContext, Row}
import org.apache.spark.sql.catalyst.errors.attachTree
-import org.apache.spark.sql.catalyst.expressions.{Attribute, RowOrdering}
+import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.physical._
import org.apache.spark.sql.catalyst.rules.Rule
import org.apache.spark.util.MutablePair
+object Exchange {
+ /** Returns true when the ordering expressions are a subset of the key.
*/
+ def canSortWithShuffle(partitioning: Partitioning, desiredOrdering:
Seq[SortOrder]): Boolean = {
--- End diff --
It will be good to also explain that we need the ordering expressions to be
a subset of the key because we are taking advantage of `ShuffledRDD`'s
`KeyOrdering` for sorting.
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