Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/13494#discussion_r68881745
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/MetadataOnlyOptimizer.scala
---
@@ -0,0 +1,171 @@
+/*
+ * 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 org.apache.spark.sql.{AnalysisException, SparkSession}
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.catalog.{CatalogRelation,
SessionCatalog}
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.expressions.aggregate._
+import org.apache.spark.sql.catalyst.plans.logical._
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.execution.datasources.{HadoopFsRelation,
LogicalRelation}
+
+/**
+ * When scanning only partition columns, get results based on metadata
without scanning files.
+ * It is used for distinct, distinct aggregations or distinct-like
aggregations(example: Max/Min).
+ * First of all, scanning only partition columns are required, then the
rule does the following
+ * things here:
+ * 1. aggregate expression is partition columns,
+ * e.g. SELECT col FROM tbl GROUP BY col or SELECT col FROM tbl GROUP BY
cube(col).
+ * 2. aggregate function on partition columns with DISTINCT,
+ * e.g. SELECT count(DISTINCT col) FROM tbl GROUP BY col.
+ * 3. aggregate function on partition columns which have same result with
DISTINCT keyword.
+ * e.g. SELECT Max(col2) FROM tbl GROUP BY col1.
+ */
+case class MetadataOnlyOptimizer(
+ sparkSession: SparkSession,
+ catalog: SessionCatalog) extends Rule[LogicalPlan] {
+
+ private def canSupportMetadataOnly(a: Aggregate): Boolean = {
+ val aggregateExpressions = a.aggregateExpressions.flatMap { expr =>
--- End diff --
where do we check it only requires partition columns?
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