Github user lianhuiwang commented on a diff in the pull request:
https://github.com/apache/spark/pull/13494#discussion_r70247856
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/OptimizeMetadataOnlyQuery.scala
---
@@ -0,0 +1,143 @@
+/*
+ * 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.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}
+import org.apache.spark.sql.internal.SQLConf
+
+/**
+ * This rule optimizes the execution of queries that can be answered by
looking only at
+ * partition-level metadata. This applies when all the columns scanned are
partition columns, and
+ * the query has an aggregate operator that satisfies the following
conditions:
+ * 1. aggregate expression is partition columns.
+ * e.g. SELECT col FROM tbl GROUP BY col.
+ * 2. aggregate function on partition columns with DISTINCT.
+ * e.g. SELECT col1, count(DISTINCT col2) FROM tbl GROUP BY col1.
+ * 3. aggregate function on partition columns which have same result w or
w/o DISTINCT keyword.
+ * e.g. SELECT col1, Max(col2) FROM tbl GROUP BY col1.
+ */
+case class OptimizeMetadataOnlyQuery(
+ catalog: SessionCatalog,
+ conf: SQLConf) extends Rule[LogicalPlan] {
+
+ def apply(plan: LogicalPlan): LogicalPlan = {
+ if (!conf.optimizerMetadataOnly) {
+ return plan
+ }
+
+ plan.transform {
+ case a @ Aggregate(_, aggExprs, child @
PartitionedRelation(partAttrs, relation)) =>
+ // We only apply this optimization when only partitioned
attributes are scanned.
+ if (a.references.subsetOf(partAttrs)) {
+ val aggFunctions = aggExprs.flatMap(_.collect {
+ case agg: AggregateExpression => agg
+ })
+ val isAllDistinctAgg = aggFunctions.forall { agg =>
+ agg.isDistinct || (agg.aggregateFunction match {
+ // `Max` and `Min` are always distinct aggregate functions
no matter they have
+ // DISTINCT keyword or not, as the result will be same.
+ case _: Max => true
--- End diff --
Yes, we need to handle them.
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