[GitHub] [spark] ulysses-you commented on a diff in pull request #40262: [SPARK-42651][SQL] Optimize global sort to driver sort

["ulysses-you (via GitHub)" <gi...@apache.org>]

ulysses-you commented on code in PR #40262:
URL: https://github.com/apache/spark/pull/40262#discussion_r1133461951


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sql/core/src/main/scala/org/apache/spark/sql/execution/DriverSortExec.scala:
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@@ -0,0 +1,73 @@
+/*
+ * 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.execution
+
+import java.util.concurrent.TimeUnit.NANOSECONDS
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.{Attribute, NamedExpression, SortOrder, UnsafeProjection}
+import org.apache.spark.sql.catalyst.expressions.codegen.LazilyGeneratedOrdering
+import org.apache.spark.sql.catalyst.plans.physical.{Partitioning, SinglePartition}
+import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
+
+/**
+ * A special operator for global [[SortExec]] if it is the root node with/without [[ProjectExec]].
+ */
+case class DriverSortExec(

Review Comment:
   We have a rule `EliminateLimits` to remove limit if it's large enough, i.e., the actually row count is less than or equal to limit number. So if the `Sort` is the root node that means:
   1. the user does not specify the limit
   2. the limit has no meaning and has been eliminated
   
   I think if the data size is small enough, `DriverSortExec` is faster than `TakeOrderedAndProjectExec`:
   - `DriverSortExec` only sort data once at driver side
   - `TakeOrderedAndProjectExec` sort the data at executor side then merge the sorted data at driver side



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