[SPARK-35984][SQL][TEST] Config to force applying shuffled hash join

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala

@@ -27,6 +27,7 @@ import org.apache.spark.sql.catalyst.rules._
 import org.apache.spark.sql.catalyst.trees.TreePattern._
 import org.apache.spark.sql.errors.QueryCompilationErrors
 import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.util.Utils
 
 /**
  * Reorder the joins and push all the conditions into join, so that the bottom ones have at least
@@ -274,14 +275,16 @@ trait JoinSelectionHelper {
     } else {
       hintToPreferShuffleHashJoinLeft(hint) ||
         (!conf.preferSortMergeJoin && canBuildLocalHashMapBySize(left, conf) &&
-          muchSmaller(left, right))
+          muchSmaller(left, right)) ||
+        forceApplyShuffledHashJoin(conf)
     }
     val buildRight = if (hintOnly) {
       hintToShuffleHashJoinRight(hint)
     } else {
       hintToPreferShuffleHashJoinRight(hint) ||
         (!conf.preferSortMergeJoin && canBuildLocalHashMapBySize(right, conf) &&
-          muchSmaller(right, left))
+          muchSmaller(right, left)) ||
+        forceApplyShuffledHashJoin(conf)
     }
     getBuildSide(
       canBuildShuffledHashJoinLeft(joinType) && buildLeft,
@@ -424,5 +427,14 @@ trait JoinSelectionHelper {
   private def muchSmaller(a: LogicalPlan, b: LogicalPlan): Boolean = {
     a.stats.sizeInBytes * 3 <= b.stats.sizeInBytes
   }
+
+  /**
+   * Returns whether a shuffled hash join should be force applied.
+   * The config key is hard-coded because it's testing only and should not be exposed.
+   */
+  private def forceApplyShuffledHashJoin(conf: SQLConf): Boolean = {
+    Utils.isTesting &&
+      conf.getConfString("spark.sql.join.forceApplyShuffledHashJoin", "false") == "true"
+  }
 }
 

sql/core/src/test/resources/sql-tests/inputs/postgreSQL/join.sql

@@ -13,7 +13,7 @@
 
 --CONFIG_DIM1 spark.sql.autoBroadcastJoinThreshold=10485760
 --CONFIG_DIM1 spark.sql.autoBroadcastJoinThreshold=-1,spark.sql.join.preferSortMergeJoin=true
---CONFIG_DIM1 spark.sql.autoBroadcastJoinThreshold=-1,spark.sql.join.preferSortMergeJoin=false
+--CONFIG_DIM1 spark.sql.autoBroadcastJoinThreshold=-1,spark.sql.join.forceApplyShuffledHashJoin=true
 
 --CONFIG_DIM2 spark.sql.codegen.wholeStage=true
 --CONFIG_DIM2 spark.sql.codegen.wholeStage=false,spark.sql.codegen.factoryMode=CODEGEN_ONLY

sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala

@@ -1394,4 +1394,12 @@ class JoinSuite extends QueryTest with SharedSparkSession with AdaptiveSparkPlan
       checkAnswer(fullJoinDF, Row(100))
     }
   }
+
+  test("SPARK-35984: Config to force applying shuffled hash join") {
+    val sql = "SELECT * FROM testData JOIN testData2 ON key = a"
+    assertJoin(sql, classOf[SortMergeJoinExec])
+    withSQLConf("spark.sql.join.forceApplyShuffledHashJoin" -> "true") {
+      assertJoin(sql, classOf[ShuffledHashJoinExec])
+    }
+  }
 }