Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/1134#discussion_r14678203
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins.scala ---
@@ -400,3 +401,73 @@ case class BroadcastNestedLoopJoin(
streamedPlusMatches.flatMap(_._1),
sqlContext.sparkContext.makeRDD(rightOuterMatches))
}
}
+
+/**
+ * :: DeveloperApi ::
+ * In some case ,data skew happens.SkewJoin sample the table rdd to find
the largest key,
+ * then make the largest key rows as a table rdd.The left rdd will be made
leftSkewedtable
+ * rdd without the largest key and the maxkeyskewedtable rdd with the
largest key.
+ * Then,join the two table with the righttable.
+ * Finally,union the two result rdd.
+ */
+@DeveloperApi
+case class SkewJoinCartesianProduct(
+ left: SparkPlan,
+ right: SparkPlan,
+ condition: Option[Expression])(@transient sc: SparkContext) extends
BinaryNode {
+ override def output = left.output ++ right.output
+
+ @transient lazy val boundCondition =
+ InterpretedPredicate(
+ condition
+ .map(c => BindReferences.bindReference(c, left.output ++
right.output))
+ .getOrElse(Literal(true)))
+
+ def execute() = {
+
+ val skewedTable = left.execute()
+ //This will later write as configuration
+ val sample = skewedTable.sample(false, 0.3, 9).collect()
+ val sortedSample = sample.sortWith((row1, row2) => row1.hashCode() >
row2.hashCode())
+ var max = 0
+ var num = sample.size - 1
+ var temp = 0
+ var maxrowKey = sortedSample(0)
+ //find the largest key
+ if (sortedSample.size > 1) {
+ for (i <- 1 to num) {
+ if (sortedSample(i - 1) == sortedSample(i)) {
+ temp += 1
+ }
+ else {
+ if (temp > max) {
+ max = temp
+ maxrowKey = sortedSample(i - 1)
+ }
+ temp = 0
+ }
+ }
+ }
+ // I also Send a Pull Request as RDD API span fun to offer the
function
+ //split a RDD as two through span function
+ // .https://github.com/apache/spark/pull/1306
+ // val (maxKeySkewedTable, mainSkewedTable) = skewedTable.span(row
=> {
+ //
skewSideKeyGenerator(row).toString().equals(maxrowKey.toString())
+ // })
+ val maxKeySkewedTable = skewedTable.filter(row => {
+ row.toString().equals(maxrowKey.toString())
--- End diff --
Why are you comparing the strings of the rows instead of the rows
themselves?
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