[GitHub] [spark] dongjoon-hyun commented on a change in pull request #31691: [SPARK-34575][SQL] Push down limit through window when partitionSpec is empty

[GitBox <gi...@apache.org>]

dongjoon-hyun commented on a change in pull request #31691:
URL: https://github.com/apache/spark/pull/31691#discussion_r594583640



##########
File path: sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/LimitPushdownThroughWindowSuite.scala
##########
@@ -0,0 +1,190 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.optimizer
+
+import org.apache.spark.sql.Row
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.dsl.plans._
+import org.apache.spark.sql.catalyst.expressions.{CurrentRow, Rank, RowFrame, RowNumber, SpecifiedWindowFrame, UnboundedPreceding}
+import org.apache.spark.sql.catalyst.plans._
+import org.apache.spark.sql.catalyst.plans.logical._
+import org.apache.spark.sql.catalyst.rules._
+import org.apache.spark.sql.internal.SQLConf
+
+class LimitPushdownThroughWindowSuite extends PlanTest {
+  // CollapseProject and RemoveNoopOperators is needed because we need it to collapse project.
+  private val limitPushdownRules = Seq(
+    CollapseProject,
+    RemoveNoopOperators,
+    LimitPushDownThroughWindow,
+    EliminateLimits,
+    ConstantFolding,
+    BooleanSimplification)
+
+  private object Optimize extends RuleExecutor[LogicalPlan] {
+    val batches =
+      Batch("Limit pushdown through window", FixedPoint(100),
+        limitPushdownRules: _*) :: Nil
+  }
+
+  private object WithoutOptimize extends RuleExecutor[LogicalPlan] {
+    val batches =
+      Batch("Without limit pushdown through window", FixedPoint(100),
+        limitPushdownRules
+          .filterNot(_.ruleName.equals(LimitPushDownThroughWindow.ruleName)): _*) :: Nil
+  }
+
+  private val testRelation = LocalRelation.fromExternalRows(
+    Seq("a".attr.int, "b".attr.int, "c".attr.int),
+    1.to(6).map(_ => Row(1, 2, 3)))
+
+  private val a = testRelation.output(0)
+  private val b = testRelation.output(1)
+  private val c = testRelation.output(2)
+  private val windowFrame = SpecifiedWindowFrame(RowFrame, UnboundedPreceding, CurrentRow)
+
+  test("Push down limit through window when partitionSpec is empty") {
+    val originalQuery = testRelation
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"))
+      .limit(2)
+    val correctAnswer = testRelation
+      .select(a, b, c)
+      .orderBy(c.desc)
+      .limit(2)
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"))
+
+    comparePlans(
+      Optimize.execute(originalQuery.analyze),
+      WithoutOptimize.execute(correctAnswer.analyze))
+  }
+
+  test("Push down limit through window for multiple window functions") {
+    val originalQuery = testRelation
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"),
+        windowExpr(new Rank(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rk"))
+      .limit(2)
+    val correctAnswer = testRelation
+      .select(a, b, c)
+      .orderBy(c.desc)
+      .limit(2)
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"),
+        windowExpr(new Rank(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rk"))
+
+    comparePlans(
+      Optimize.execute(originalQuery.analyze),
+      WithoutOptimize.execute(correctAnswer.analyze))
+  }
+
+  test("Push down limit through window respect spark.sql.execution.topKSortFallbackThreshold") {
+    Seq(1, 100).foreach { threshold =>
+      withSQLConf(SQLConf.TOP_K_SORT_FALLBACK_THRESHOLD.key -> threshold.toString) {
+        val originalQuery = testRelation
+          .select(a, b, c,
+            windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"))
+          .limit(2)
+        val correctAnswer = if (threshold == 1) {
+          originalQuery
+        } else {
+          testRelation
+            .select(a, b, c)
+            .orderBy(c.desc)
+            .limit(2)
+            .select(a, b, c,
+              windowExpr(RowNumber(), windowSpec(Nil, c.desc :: Nil, windowFrame)).as("rn"))
+        }
+
+        comparePlans(
+          Optimize.execute(originalQuery.analyze),
+          WithoutOptimize.execute(correctAnswer.analyze))
+      }
+    }
+  }
+
+  test("Push down to first window if order column is different") {
+    val originalQuery = testRelation
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, b.desc :: Nil, windowFrame)).as("rn"),
+        windowExpr(new Rank(), windowSpec(Nil, c.asc :: Nil, windowFrame)).as("rk"))
+      .limit(2)
+    val correctAnswer = testRelation
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(Nil, b.desc :: Nil, windowFrame)).as("rn"))
+      .orderBy(c.asc)
+      .limit(2)
+      .select(a, b, c, $"rn".attr,
+        windowExpr(new Rank(), windowSpec(Nil, c.asc :: Nil, windowFrame)).as("rk"))
+
+    comparePlans(
+      Optimize.execute(originalQuery.analyze),
+      WithoutOptimize.execute(correctAnswer.analyze))
+  }
+
+  test("Push down if there is a Project between LocalLimit and Window") {
+    val originalQuery = testRelation
+      .select(a, b,
+        windowExpr(RowNumber(), windowSpec(Nil, b.desc :: Nil, windowFrame)).as("rn"))
+      .select(a, $"rn".attr)
+      .limit(2)
+    val correctAnswer = testRelation
+      .select(a, b)
+      .orderBy(b.desc)
+      .limit(2)
+      .select(a, windowExpr(RowNumber(), windowSpec(Nil, b.desc :: Nil, windowFrame)).as("rn"))
+
+    comparePlans(
+      Optimize.execute(originalQuery.analyze),
+      WithoutOptimize.execute(correctAnswer.analyze))
+  }
+
+  test("Should not push down if partitionSpec is not empty") {
+    val originalQuery = testRelation
+      .select(a, b, c,
+        windowExpr(RowNumber(), windowSpec(a :: Nil, c.desc :: Nil, windowFrame)).as("rn"))
+      .limit(20)

Review comment:
       To test `partitionSpec is not empty` independently, we need `.limit(2)`, don't we?




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