Github user chenghao-intel commented on a diff in the pull request:
https://github.com/apache/spark/pull/1134#discussion_r14111131
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins.scala ---
@@ -341,3 +342,85 @@ case class BroadcastNestedLoopJoin(
streamedPlusMatches.flatMap(_._1), sc.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 streamed rdd will be
made as mainstreamedtable
+ * rdd without the largest key and the maxkeystreamedtable rdd with the
largest key.Then,join the two table with the buildtable.
+ * Finally,union the two result rdd.
+ */
+@DeveloperApi
+case class SkewJoin(
+ leftKeys: Seq[Expression],
+ rightKeys: Seq[Expression],
+ buildSide: BuildSide,
+ left: SparkPlan,
+ right: SparkPlan,
+ @transient sc: SparkContext) extends BinaryNode
{
+ override def outputPartitioning: Partitioning = left.outputPartitioning
+
+ override def requiredChildDistribution =
+ ClusteredDistribution(leftKeys) ::
ClusteredDistribution(rightKeys) :: Nil
+
+ val (buildPlan, streamedPlan) = buildSide match {
+ case BuildLeft => (left, right)
+ case BuildRight => (right, left)
+ }
+ val (buildKeys, streamedKeys) = buildSide match {
+ case BuildLeft => (leftKeys, rightKeys)
+ case BuildRight => (rightKeys, leftKeys)
+ }
+
+ def output = left.output ++ right.output
+
+ @transient lazy val buildSideKeyGenerator = new Projection(buildKeys,
buildPlan.output)
+ @transient lazy val streamSideKeyGenerator = new
Projection(streamedKeys, streamedPlan.output)
+
+
+ def execute() = {
+ val streamedTable = streamedPlan.execute()
+ //This will later write as configuration
+ val sample = streamedTable.sample(false, 0.3, 9).map(row =>
streamSideKeyGenerator(row)).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
+ }
+ }
+ }
+ val maxKeyStreamedTable = streamedTable.filter(row => {
--- End diff --
This can be done like
```
val (maxKeyStreamedTable, mainStreamedTable) = streamedTable.partition(row
=> {
streamSideKeyGenerator(row).toString().equals(maxrowKey.toString())
})
```
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