[SPARK-31869][SQL] BroadcastHashJoinExec can utilize the build side for its output partitioning

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -2665,6 +2665,15 @@ object SQLConf {
       .checkValue(_ > 0, "The difference must be positive.")
       .createWithDefault(4)
 
+  val BROADCAST_HASH_JOIN_OUTPUT_PARTITIONING_EXPAND_LIMIT =
+    buildConf("spark.sql.execution.broadcastHashJoin.outputPartitioningExpandLimit")
+      .doc("The maximum number of partitionings that a HashPartitioning can be expanded to. " +
+        "This configuration is applicable only for inner joins.")
+      .version("3.1.0")
+      .intConf
+      .checkValue(_ > 0, "The value must be positive.")
+      .createWithDefault(8)
+
   /**
    * Holds information about keys that have been deprecated.
    *

sql/core/src/main/scala/org/apache/spark/sql/execution/joins/BroadcastHashJoinExec.scala

@@ -17,6 +17,8 @@
 
 package org.apache.spark.sql.execution.joins
 
+import scala.collection.mutable
+
 import org.apache.spark.TaskContext
 import org.apache.spark.broadcast.Broadcast
 import org.apache.spark.rdd.RDD
@@ -26,9 +28,10 @@ import org.apache.spark.sql.catalyst.expressions.codegen._
 import org.apache.spark.sql.catalyst.expressions.codegen.Block._
 import org.apache.spark.sql.catalyst.optimizer.{BuildLeft, BuildRight, BuildSide}
 import org.apache.spark.sql.catalyst.plans._
-import org.apache.spark.sql.catalyst.plans.physical.{BroadcastDistribution, Distribution, UnspecifiedDistribution}
+import org.apache.spark.sql.catalyst.plans.physical.{BroadcastDistribution, Distribution, HashPartitioning, Partitioning, PartitioningCollection, UnspecifiedDistribution}
 import org.apache.spark.sql.execution.{CodegenSupport, SparkPlan}
 import org.apache.spark.sql.execution.metric.SQLMetrics
+import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.types.{BooleanType, LongType}
 
 /**
@@ -51,7 +54,7 @@ case class BroadcastHashJoinExec(
     "numOutputRows" -> SQLMetrics.createMetric(sparkContext, "number of output rows"))
 
   override def requiredChildDistribution: Seq[Distribution] = {
-    val mode = HashedRelationBroadcastMode(buildKeys)
+    val mode = HashedRelationBroadcastMode(buildBoundKeys)
     buildSide match {
       case BuildLeft =>
         BroadcastDistribution(mode) :: UnspecifiedDistribution :: Nil
@@ -60,6 +63,81 @@ case class BroadcastHashJoinExec(
     }
   }
 
+  override lazy val outputPartitioning: Partitioning = {
+    joinType match {
+      case Inner =>
+        streamedPlan.outputPartitioning match {
+          case h: HashPartitioning => expandOutputPartitioning(h)
+          case c: PartitioningCollection => expandOutputPartitioning(c)
+          case other => other
+        }
+      case _ => streamedPlan.outputPartitioning
+    }
+  }
+
+  // An one-to-many mapping from a streamed key to build keys.
+  private lazy val streamedKeyToBuildKeyMapping = {
+    val mapping = mutable.Map.empty[Expression, Seq[Expression]]
+    streamedKeys.zip(buildKeys).foreach {
+      case (streamedKey, buildKey) =>
+        val key = streamedKey.canonicalized
+        mapping.get(key) match {
+          case Some(v) => mapping.put(key, v :+ buildKey)
+          case None => mapping.put(key, Seq(buildKey))
+        }
+    }
+    mapping.toMap
+  }
+
+  // Expands the given partitioning collection recursively.
+  private def expandOutputPartitioning(
+      partitioning: PartitioningCollection): PartitioningCollection = {
+    PartitioningCollection(partitioning.partitionings.flatMap {
+      case h: HashPartitioning => expandOutputPartitioning(h).partitionings
+      case c: PartitioningCollection => Seq(expandOutputPartitioning(c))
+      case other => Seq(other)
+    })
+  }
+
+  // Expands the given hash partitioning by substituting streamed keys with build keys.
+  // For example, if the expressions for the given partitioning are Seq("a", "b", "c")
+  // where the streamed keys are Seq("b", "c") and the build keys are Seq("x", "y"),
+  // the expanded partitioning will have the following expressions:
+  // Seq("a", "b", "c"), Seq("a", "b", "y"), Seq("a", "x", "c"), Seq("a", "x", "y").
+  // The expanded expressions are returned as PartitioningCollection.
+  private def expandOutputPartitioning(partitioning: HashPartitioning): PartitioningCollection = {
+    val maxNumCombinations = sqlContext.conf.getConf(
+      SQLConf.BROADCAST_HASH_JOIN_OUTPUT_PARTITIONING_EXPAND_LIMIT)
+    var currentNumCombinations = 0
+
+    def generateExprCombinations(
+        current: Seq[Expression],
+        accumulated: Seq[Expression]): Seq[Seq[Expression]] = {
+      if (currentNumCombinations > maxNumCombinations) {
+        Nil
+      } else if (current.isEmpty) {
+        currentNumCombinations += 1
+        Seq(accumulated)
+      } else {
+        val buildKeys = streamedKeyToBuildKeyMapping.get(current.head.canonicalized)
+        generateExprCombinations(current.tail, accumulated :+ current.head) ++
+          buildKeys.map { bKeys =>
+            bKeys.flatMap { bKey =>
+              if (currentNumCombinations < maxNumCombinations) {
+                generateExprCombinations(current.tail, accumulated :+ bKey)
+              } else {
+                Nil
+              }
+            }
+          }.getOrElse(Nil)
+      }
+    }
+
+    PartitioningCollection(
+      generateExprCombinations(partitioning.expressions, Nil)
+        .map(HashPartitioning(_, partitioning.numPartitions)))
+  }
+
   protected override def doExecute(): RDD[InternalRow] = {
     val numOutputRows = longMetric("numOutputRows")
 
@@ -135,13 +213,13 @@ case class BroadcastHashJoinExec(
       ctx: CodegenContext,
       input: Seq[ExprCode]): (ExprCode, String) = {
     ctx.currentVars = input
-    if (streamedKeys.length == 1 && streamedKeys.head.dataType == LongType) {
+    if (streamedBoundKeys.length == 1 && streamedBoundKeys.head.dataType == LongType) {
       // generate the join key as Long
-      val ev = streamedKeys.head.genCode(ctx)
+      val ev = streamedBoundKeys.head.genCode(ctx)
       (ev, ev.isNull)
     } else {
       // generate the join key as UnsafeRow
-      val ev = GenerateUnsafeProjection.createCode(ctx, streamedKeys)
+      val ev = GenerateUnsafeProjection.createCode(ctx, streamedBoundKeys)
       (ev, s"${ev.value}.anyNull()")
     }
   }

sql/core/src/main/scala/org/apache/spark/sql/execution/joins/HashJoin.scala

@@ -62,21 +62,30 @@ trait HashJoin extends BaseJoinExec {
   protected lazy val (buildKeys, streamedKeys) = {
     require(leftKeys.map(_.dataType) == rightKeys.map(_.dataType),
       "Join keys from two sides should have same types")
-    val lkeys = bindReferences(HashJoin.rewriteKeyExpr(leftKeys), left.output)
-    val rkeys = bindReferences(HashJoin.rewriteKeyExpr(rightKeys), right.output)
     buildSide match {
-      case BuildLeft => (lkeys, rkeys)
-      case BuildRight => (rkeys, lkeys)
+      case BuildLeft => (leftKeys, rightKeys)
+      case BuildRight => (rightKeys, leftKeys)
     }
   }
 
+  private lazy val (buildOutput, streamedOutput) = {
+    buildSide match {
+      case BuildLeft => (left.output, right.output)
+      case BuildRight => (right.output, left.output)
+    }
+  }
+
+  protected lazy val buildBoundKeys =
+    bindReferences(HashJoin.rewriteKeyExpr(buildKeys), buildOutput)
 
+  protected lazy val streamedBoundKeys =
+    bindReferences(HashJoin.rewriteKeyExpr(streamedKeys), streamedOutput)
 
   protected def buildSideKeyGenerator(): Projection =
-    UnsafeProjection.create(buildKeys)
+    UnsafeProjection.create(buildBoundKeys)
 
   protected def streamSideKeyGenerator(): UnsafeProjection =
-    UnsafeProjection.create(streamedKeys)
+    UnsafeProjection.create(streamedBoundKeys)
 
   @transient private[this] lazy val boundCondition = if (condition.isDefined) {
     Predicate.create(condition.get, streamedPlan.output ++ buildPlan.output).eval _

sql/core/src/main/scala/org/apache/spark/sql/execution/joins/ShuffledHashJoinExec.scala

@@ -55,7 +55,8 @@ case class ShuffledHashJoinExec(
     val buildTime = longMetric("buildTime")
     val start = System.nanoTime()
     val context = TaskContext.get()
-    val relation = HashedRelation(iter, buildKeys, taskMemoryManager = context.taskMemoryManager())
+    val relation = HashedRelation(
+      iter, buildBoundKeys, taskMemoryManager = context.taskMemoryManager())
     buildTime += NANOSECONDS.toMillis(System.nanoTime() - start)
     buildDataSize += relation.estimatedSize
     // This relation is usually used until the end of task.

sql/core/src/test/scala/org/apache/spark/sql/execution/adaptive/AdaptiveQueryExecSuite.scala

@@ -565,7 +565,7 @@ class AdaptiveQueryExecSuite
       val smj = findTopLevelSortMergeJoin(plan)
       assert(smj.size == 2)
       val smj2 = findTopLevelSortMergeJoin(adaptivePlan)
-      assert(smj2.size == 2, origPlan.toString)
+      assert(smj2.size == 1, origPlan.toString)
     }
   }