[SPARK-22390][SPARK-32833][SQL] JDBC V2 Datasource aggregate push down

docs/sql-data-sources-jdbc.md

@@ -211,6 +211,13 @@ the following case-insensitive options:
      Specifies kerberos principal name for the JDBC client. If both <code>keytab</code> and <code>principal</code> are defined then Spark tries to do kerberos authentication.
     </td>
   </tr>
+
+  <tr>
+    <td><code>pushDownAggregate</code></td>
+    <td>
+     The option to enable or disable aggregate push-down into the JDBC data source. The default value is false, in which case Spark will NOT push down aggregates to the JDBC data source. Otherwise, if set to true, aggregate will be pushed down to the JDBC data source and thus aggregates will be handled by data source instead of Spark. Aggregate push-down is usually turned off when the aggregate is performed faster by Spark than by the JDBC data source. Please note that aggregates are pushed down if and only if all the aggregates and the related filters can be pushed down.
+    </td>
+  </tr>
 </table>
 
 Note that kerberos authentication with keytab is not always supported by the JDBC driver.<br>

sql/catalyst/src/main/java/org/apache/spark/sql/connector/read/SupportsPushDownAggregates.java

@@ -0,0 +1,44 @@
+/*
+ * 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.connector.read;
+
+import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.sources.Aggregation;
+
+/**
+ * A mix-in interface for {@link ScanBuilder}. Data sources can implement this interface to
+ * push down aggregates to the data source.
+ *
+ * @since 3.2.0
+ */
+@Evolving
+public interface SupportsPushDownAggregates extends ScanBuilder {
+
+  /**
+   * Pushes down Aggregation to datasource.
+   * The Aggregation can be pushed down only if all the Aggregate Functions can
+   * be pushed down.
+   */
+  void pushAggregation(Aggregation aggregation);
+
+  /**
+   * Returns the aggregation that are pushed to the data source via
+   * {@link #pushAggregation(Aggregation aggregation)}.
+   */
+  Aggregation pushedAggregation();
+}

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Count.scala

@@ -17,11 +17,7 @@
 
 package org.apache.spark.sql.catalyst.expressions.aggregate
 
-import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
-import org.apache.spark.sql.catalyst.dsl.expressions._
 import org.apache.spark.sql.catalyst.expressions._
-import org.apache.spark.sql.internal.SQLConf
-import org.apache.spark.sql.types._
 
 // scalastyle:off line.size.limit
 @ExpressionDescription(
@@ -44,52 +40,7 @@ import org.apache.spark.sql.types._
   group = "agg_funcs",
   since = "1.0.0")
 // scalastyle:on line.size.limit
-case class Count(children: Seq[Expression]) extends DeclarativeAggregate {
-
-  override def nullable: Boolean = false
-
-  // Return data type.
-  override def dataType: DataType = LongType
-
-  override def checkInputDataTypes(): TypeCheckResult = {
-    if (children.isEmpty && !SQLConf.get.getConf(SQLConf.ALLOW_PARAMETERLESS_COUNT)) {
-      TypeCheckResult.TypeCheckFailure(s"$prettyName requires at least one argument. " +
-        s"If you have to call the function $prettyName without arguments, set the legacy " +
-        s"configuration `${SQLConf.ALLOW_PARAMETERLESS_COUNT.key}` as true")
-    } else {
-      TypeCheckResult.TypeCheckSuccess
-    }
-  }
-
-  protected lazy val count = AttributeReference("count", LongType, nullable = false)()
-
-  override lazy val aggBufferAttributes = count :: Nil
-
-  override lazy val initialValues = Seq(
-    /* count = */ Literal(0L)
-  )
-
-  override lazy val mergeExpressions = Seq(
-    /* count = */ count.left + count.right
-  )
-
-  override lazy val evaluateExpression = count
-
-  override def defaultResult: Option[Literal] = Option(Literal(0L))
-
-  override lazy val updateExpressions = {
-    val nullableChildren = children.filter(_.nullable)
-    if (nullableChildren.isEmpty) {
-      Seq(
-        /* count = */ count + 1L
-      )
-    } else {
-      Seq(
-        /* count = */ If(nullableChildren.map(IsNull).reduce(Or), count, count + 1L)
-      )
-    }
-  }
-}
+case class Count(children: Seq[Expression]) extends CountBase(children)
 
 object Count {
   def apply(child: Expression): Count = Count(child :: Nil)

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/CountBase.scala

@@ -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.catalyst.expressions.aggregate
+
+import org.apache.spark.sql.catalyst.analysis.TypeCheckResult
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types._
+
+abstract class CountBase(children: Seq[Expression]) extends DeclarativeAggregate {
+
+  override def nullable: Boolean = false
+
+  // Return data type.
+  override def dataType: DataType = LongType
+
+  override def checkInputDataTypes(): TypeCheckResult = {
+    if (children.isEmpty && !SQLConf.get.getConf(SQLConf.ALLOW_PARAMETERLESS_COUNT)) {
+      TypeCheckResult.TypeCheckFailure(s"$prettyName requires at least one argument. " +
+        s"If you have to call the function $prettyName without arguments, set the legacy " +
+        s"configuration `${SQLConf.ALLOW_PARAMETERLESS_COUNT.key}` as true")
+    } else {
+      TypeCheckResult.TypeCheckSuccess
+    }
+  }
+
+  protected lazy val count = AttributeReference("count", LongType, nullable = false)()
+
+  override lazy val aggBufferAttributes = count :: Nil
+
+  override lazy val initialValues = Seq(
+    /* count = */ Literal(0L)
+  )
+
+  override lazy val mergeExpressions = Seq(
+    /* count = */ count.left + count.right
+  )
+
+  override lazy val evaluateExpression = count
+
+  override def defaultResult: Option[Literal] = Option(Literal(0L))
+
+  override lazy val updateExpressions = {
+    val nullableChildren = children.filter(_.nullable)
+    if (nullableChildren.isEmpty) {
+      Seq(
+        /* count = */ count + 1L
+      )
+    } else {
+      Seq(
+        /* count = */ If(nullableChildren.map(IsNull).reduce(Or), count, count + 1L)
+      )
+    }
+  }
+}
+
+

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/PushDownCount.scala

@@ -0,0 +1,41 @@
+/*
+ * 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.expressions.aggregate
+
+import org.apache.spark.sql.catalyst.dsl.expressions._
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.types.LongType
+
+case class PushDownCount(children: Seq[Expression]) extends CountBase(children) {
+
+  override protected lazy val count =
+    AttributeReference("PushDownCount", LongType, nullable = false)()
+
+  override lazy val updateExpressions = {
+    Seq(
+      // if count is pushed down to Data Source layer, add the count result retrieved from
+      // Data Source
+      /* count = */ count + children.head
+    )
+  }
+}
+
+object PushDownCount {
+  def apply(child: Expression): PushDownCount =
+    PushDownCount(child :: Nil)
+}

sql/catalyst/src/main/scala/org/apache/spark/sql/sources/aggregates.scala

@@ -0,0 +1,36 @@
+/*
+ * 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.sources
+
+import org.apache.spark.sql.types.DataType
+
+case class Aggregation(aggregateExpressions: Seq[AggregateFunc],
+                       groupByExpressions: Seq[String])
+
+abstract class AggregateFunc
+
+case class Avg(column: String, dataType: DataType, isDistinct: Boolean) extends AggregateFunc
+case class Min(column: String, dataType: DataType) extends AggregateFunc
+case class Max(column: String, dataType: DataType) extends AggregateFunc
+case class Sum(column: String, dataType: DataType, isDistinct: Boolean) extends AggregateFunc
+case class Count(column: String, dataType: DataType, isDistinct: Boolean) extends AggregateFunc
+
+object Aggregation {
+  // Returns an empty Aggregate
+  def empty: Aggregation = Aggregation(Seq.empty[AggregateFunc], Seq.empty[String])
+}

sql/core/src/main/scala/org/apache/spark/sql/execution/DataSourceScanExec.scala

@@ -35,7 +35,7 @@ import org.apache.spark.sql.execution.datasources._
 import org.apache.spark.sql.execution.datasources.parquet.{ParquetFileFormat => ParquetSource}
 import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
 import org.apache.spark.sql.internal.SQLConf
-import org.apache.spark.sql.sources.{BaseRelation, Filter}
+import org.apache.spark.sql.sources.{Aggregation, BaseRelation, Filter}
 import org.apache.spark.sql.types.StructType
 import org.apache.spark.sql.vectorized.ColumnarBatch
 import org.apache.spark.util.Utils
@@ -102,6 +102,7 @@ case class RowDataSourceScanExec(
     requiredSchema: StructType,
     filters: Set[Filter],
     handledFilters: Set[Filter],
+    aggregation: Aggregation,
     rdd: RDD[InternalRow],
     @transient relation: BaseRelation,
     tableIdentifier: Option[TableIdentifier])
@@ -132,9 +133,17 @@ case class RowDataSourceScanExec(
     val markedFilters = for (filter <- filters) yield {
       if (handledFilters.contains(filter)) s"*$filter" else s"$filter"
     }
+    val markedAggregates = for (aggregate <- aggregation.aggregateExpressions) yield {
+      s"*$aggregate"
+    }
+    val markedGroupby = for (groupby <- aggregation.groupByExpressions) yield {
+      s"*$groupby"
+    }
     Map(
       "ReadSchema" -> requiredSchema.catalogString,
-      "PushedFilters" -> markedFilters.mkString("[", ", ", "]"))
+      "PushedFilters" -> markedFilters.mkString("[", ", ", "]"),
+      "PushedAggregates" -> markedAggregates.mkString("[", ", ", "]"),
+      "PushedGroupby" -> markedGroupby.mkString("[", ", ", "]"))
   }
 
   // Don't care about `rdd` and `tableIdentifier` when canonicalizing.

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSourceStrategy.scala

@@ -33,6 +33,7 @@ import org.apache.spark.sql.catalyst.catalog._
 import org.apache.spark.sql.catalyst.encoders.RowEncoder
 import org.apache.spark.sql.catalyst.expressions
 import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
 import org.apache.spark.sql.catalyst.planning.ScanOperation
 import org.apache.spark.sql.catalyst.plans.logical.{CacheTable, InsertIntoDir, InsertIntoStatement, LogicalPlan, Project, UncacheTable}
 import org.apache.spark.sql.catalyst.rules.Rule
@@ -358,6 +359,7 @@ object DataSourceStrategy
         l.output.toStructType,
         Set.empty,
         Set.empty,
+        Aggregation.empty,
         toCatalystRDD(l, baseRelation.buildScan()),
         baseRelation,
         None) :: Nil
@@ -431,6 +433,7 @@ object DataSourceStrategy
         requestedColumns.toStructType,
         pushedFilters.toSet,
         handledFilters,
+        Aggregation.empty,
         scanBuilder(requestedColumns, candidatePredicates, pushedFilters),
         relation.relation,
         relation.catalogTable.map(_.identifier))
@@ -453,6 +456,7 @@ object DataSourceStrategy
         requestedColumns.toStructType,
         pushedFilters.toSet,
         handledFilters,
+        Aggregation.empty,
         scanBuilder(requestedColumns, candidatePredicates, pushedFilters),
         relation.relation,
         relation.catalogTable.map(_.identifier))
@@ -700,6 +704,49 @@ object DataSourceStrategy
     (nonconvertiblePredicates ++ unhandledPredicates, pushedFilters, handledFilters)
   }
 
+  private def columnAsString(e: Expression): String = e match {
+    case AttributeReference(name, _, _, _) => name
+    case Cast(child, _, _) => columnAsString (child)
+    case Add(left, right, _) =>
+      columnAsString(left) + " + " + columnAsString(right)
+    case Subtract(left, right, _) =>
+      columnAsString(left) + " - " + columnAsString(right)
+    case Multiply(left, right, _) =>
+      columnAsString(left) + " * " + columnAsString(right)
+    case Divide(left, right, _) =>
+      columnAsString(left) + " / " + columnAsString(right)
+    case CheckOverflow(child, _, _) => columnAsString (child)
+    case PromotePrecision(child) => columnAsString (child)
+    case _ => ""
+  }
+
+  protected[sql] def translateAggregate(aggregates: AggregateExpression): Option[AggregateFunc] = {
+    aggregates.aggregateFunction match {
+      case min: aggregate.Min =>
+        val colName = columnAsString(min.child)
+        if (colName.nonEmpty) Some(Min(colName, min.dataType)) else None
+      case max: aggregate.Max =>
+        val colName = columnAsString(max.child)
+        if (colName.nonEmpty) Some(Max(colName, max.dataType)) else None
+      case avg: aggregate.Average =>
+        val colName = columnAsString(avg.child)
+        if (colName.nonEmpty) Some(Avg(colName, avg.dataType, aggregates.isDistinct)) else None
+      case sum: aggregate.Sum =>
+        val colName = columnAsString(sum.child)
+        if (colName.nonEmpty) Some(Sum(colName, sum.dataType, aggregates.isDistinct)) else None
+      case count: aggregate.Count =>
+        val columnName = count.children.head match {
+          case Literal(_, _) => "1"
+          case _ => columnAsString(count.children.head)
+        }
+        if (columnName.nonEmpty) {
+          Some(Count(columnName, count.dataType, aggregates.isDistinct))
+        }
+        else None
+      case _ => None
+    }
+  }
+
   /**
    * Convert RDD of Row into RDD of InternalRow with objects in catalyst types
    */