maropu commented on a change in pull request #24164: [SPARK-27225][SQL]
Implement join strategy hints
URL: https://github.com/apache/spark/pull/24164#discussion_r268015229
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/hints.scala
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@@ -66,17 +66,76 @@ object JoinHint {
/**
* The hint attributes to be applied on a specific node.
*
- * @param broadcast If set to true, it indicates that the broadcast hash join
is the preferred join
- * strategy and the node with this hint is preferred to be
the build side.
+ * @param strategy The preferred join strategy.
*/
-case class HintInfo(broadcast: Boolean = false) {
+case class HintInfo(strategy: Option[JoinStrategyHint] = None) {
+
+ /**
+ * Combine two [[HintInfo]]s into one [[HintInfo]], in which the new
strategy will the strategy
+ * in this [[HintInfo]] if defined, otherwise the strategy in the other
[[HintInfo]].
+ */
+ def merge(other: HintInfo): HintInfo = {
+ HintInfo(strategy = this.strategy.orElse(other.strategy))
+ }
override def toString: String = {
val hints = scala.collection.mutable.ArrayBuffer.empty[String]
- if (broadcast) {
- hints += "broadcast"
+ if (strategy.isDefined) {
+ hints += s"strategy=${strategy.get}"
}
if (hints.isEmpty) "none" else hints.mkString("(", ", ", ")")
}
}
+
+sealed abstract class JoinStrategyHint {
+
+ def displayName: String
+ def hintAliases: Set[String]
+
+ override def toString: String = displayName
+}
+
+/**
+ * The enumeration of join strategy hints.
+ *
+ * The hinted strategy will be used for the join with which it is associated
if doable. In case
+ * of contradicting strategy hints specified for each side of the join, hints
are prioritized as
+ * BROADCAST over SHUFFLE_MERGE over SHUFFLE_HASH over SHUFFLE_REPLICATE_NL.
+ */
+object JoinStrategyHint {
+
+ val strategies: Set[JoinStrategyHint] = Set(
+ BROADCAST,
+ SHUFFLE_MERGE,
+ SHUFFLE_HASH,
+ SHUFFLE_REPLICATE_NL)
+}
+
+case object BROADCAST extends JoinStrategyHint {
+ override def displayName: String = "broadcast-hash"
+ override def hintAliases: Set[String] = Set(
+ "BROADCAST",
+ "BROADCASTJOIN",
+ "MAPJOIN")
+}
+
+case object SHUFFLE_MERGE extends JoinStrategyHint {
+ override def displayName: String = "shuffle-merge"
+ override def hintAliases: Set[String] = Set(
+ "SHUFFLE_MERGE",
+ "MERGE",
+ "MERGEJOIN")
+}
+
+case object SHUFFLE_HASH extends JoinStrategyHint {
+ override def displayName: String = "shuffle-hash"
+ override def hintAliases: Set[String] = Set(
+ "SHUFFLE_HASH")
+}
+
+case object SHUFFLE_REPLICATE_NL extends JoinStrategyHint {
+ override def displayName: String = "shuffle-replicate-nested-loop"
+ override def hintAliases: Set[String] = Set(
+ "SHUFFLE_REPLICATE_NL")
Review comment:
This hint for cartesian products is useful for users?
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