[SPARK-2094][SQL] "Exactly once" semantics for DDL and command statements

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/commands.scala

@@ -17,7 +17,7 @@
 
 package org.apache.spark.sql.catalyst.plans.logical
 
-import org.apache.spark.sql.catalyst.expressions.{AttributeReference, Attribute}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, AttributeReference, BoundReference}
 import org.apache.spark.sql.catalyst.types.StringType
 
 /**
@@ -26,35 +26,37 @@ import org.apache.spark.sql.catalyst.types.StringType
  */
 abstract class Command extends LeafNode {
   self: Product =>
-  def output: Seq[Attribute] = Seq.empty  // TODO: SPARK-2081 should fix this
+  def output: Seq[Attribute] = Seq.empty
 }
 
 /**
  * Returned for commands supported by a given parser, but not catalyst.  In general these are DDL
  * commands that are passed directly to another system.
  */
-case class NativeCommand(cmd: String) extends Command
+case class NativeCommand(cmd: String) extends Command {
+  override def output =
+    Seq(BoundReference(0, AttributeReference("result", StringType, nullable = false)()))
+}
 
 /**
  * Commands of the form "SET (key) (= value)".
  */
 case class SetCommand(key: Option[String], value: Option[String]) extends Command {
   override def output = Seq(
-    AttributeReference("key", StringType, nullable = false)(),
-    AttributeReference("value", StringType, nullable = false)()
-  )
+    BoundReference(0, AttributeReference("key", StringType, nullable = false)()),
+    BoundReference(1, AttributeReference("value", StringType, nullable = false)()))
 }
 
 /**
  * Returned by a parser when the users only wants to see what query plan would be executed, without
  * actually performing the execution.
  */
 case class ExplainCommand(plan: LogicalPlan) extends Command {
-  override def output = Seq(AttributeReference("plan", StringType, nullable = false)())
+  override def output =
+    Seq(BoundReference(0, AttributeReference("plan", StringType, nullable = false)()))
 }
 
 /**
  * Returned for the "CACHE TABLE tableName" and "UNCACHE TABLE tableName" command.
  */
 case class CacheCommand(tableName: String, doCache: Boolean) extends Command
-

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/FilterPushdownSuite.scala

@@ -161,7 +161,7 @@ class FilterPushdownSuite extends OptimizerTest {
 
     comparePlans(optimized, correctAnswer)
   }
-  
+
   test("joins: push down left outer join #1") {
     val x = testRelation.subquery('x)
     val y = testRelation.subquery('y)

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -31,7 +31,7 @@ import org.apache.spark.sql.catalyst.{ScalaReflection, dsl}
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.types._
 import org.apache.spark.sql.catalyst.optimizer.Optimizer
-import org.apache.spark.sql.catalyst.plans.logical.{SetCommand, LogicalPlan}
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.catalyst.rules.RuleExecutor
 
 import org.apache.spark.sql.columnar.InMemoryColumnarTableScan
@@ -147,14 +147,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
    *
    * @group userf
    */
-  def sql(sqlText: String): SchemaRDD = {
-    val result = new SchemaRDD(this, parseSql(sqlText))
-    // We force query optimization to happen right away instead of letting it happen lazily like
-    // when using the query DSL.  This is so DDL commands behave as expected.  This is only
-    // generates the RDD lineage for DML queries, but do not perform any execution.
-    result.queryExecution.toRdd
-    result
-  }
+  def sql(sqlText: String): SchemaRDD = new SchemaRDD(this, parseSql(sqlText))
 
   /** Returns the specified table as a SchemaRDD */
   def table(tableName: String): SchemaRDD =
@@ -280,35 +273,14 @@ class SQLContext(@transient val sparkContext: SparkContext)
   protected abstract class QueryExecution {
     def logical: LogicalPlan
 
-    def eagerlyProcess(plan: LogicalPlan): RDD[Row] = plan match {
-      case SetCommand(key, value) =>
-        // Only this case needs to be executed eagerly. The other cases will
-        // be taken care of when the actual results are being extracted.
-        // In the case of HiveContext, sqlConf is overridden to also pass the
-        // pair into its HiveConf.
-        if (key.isDefined && value.isDefined) {
-          set(key.get, value.get)
-        }
-        // It doesn't matter what we return here, since this is only used
-        // to force the evaluation to happen eagerly.  To query the results,
-        // one must use SchemaRDD operations to extract them.
-        emptyResult
-      case _ => executedPlan.execute()
-    }
-
     lazy val analyzed = analyzer(logical)
     lazy val optimizedPlan = optimizer(analyzed)
     // TODO: Don't just pick the first one...
     lazy val sparkPlan = planner(optimizedPlan).next()
     lazy val executedPlan: SparkPlan = prepareForExecution(sparkPlan)
 
     /** Internal version of the RDD. Avoids copies and has no schema */
-    lazy val toRdd: RDD[Row] = {
-      logical match {
-        case s: SetCommand => eagerlyProcess(s)
-        case _ => executedPlan.execute()
-      }
-    }
+    lazy val toRdd: RDD[Row] = executedPlan.execute()
 
     protected def stringOrError[A](f: => A): String =
       try f.toString catch { case e: Throwable => e.toString }
@@ -330,7 +302,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
    * TODO: We only support primitive types, add support for nested types.
    */
   private[sql] def inferSchema(rdd: RDD[Map[String, _]]): SchemaRDD = {
-    val schema = rdd.first.map { case (fieldName, obj) =>
+    val schema = rdd.first().map { case (fieldName, obj) =>
       val dataType = obj.getClass match {
         case c: Class[_] if c == classOf[java.lang.String] => StringType
         case c: Class[_] if c == classOf[java.lang.Integer] => IntegerType

sql/core/src/main/scala/org/apache/spark/sql/SchemaRDDLike.scala

@@ -50,6 +50,14 @@ private[sql] trait SchemaRDDLike {
   @DeveloperApi
   lazy val queryExecution = sqlContext.executePlan(logicalPlan)
 
+  logicalPlan match {
+    // For various commands (like DDL) and queries with side effects, we force query optimization to
+    // happen right away to let these side effects take place eagerly.
+    case _: Command | _: InsertIntoTable | _: InsertIntoCreatedTable | _: WriteToFile =>
+      queryExecution.toRdd
+    case _ =>
+  }
+
   override def toString =
     s"""${super.toString}
        |== Query Plan ==

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

@@ -22,45 +22,69 @@ import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.{SQLContext, Row}
 import org.apache.spark.sql.catalyst.expressions.{GenericRow, Attribute}
 
+trait PhysicalCommand {
+  /**
+   * A concrete command should override this lazy field to wrap up any side effects caused by the
+   * command or any other computation that should be evaluated exactly once. The value of this field
+   * can be used as the contents of the corresponding RDD generated from the physical plan of this
+   * command.
+   *
+   * The `execute()` method of all the physical command classes should reference `sideEffect` so
+   * that the command can be executed eagerly right after the command query is created.
+   */
+  protected[sql] lazy val sideEffectResult: Seq[Any] = Seq.empty[Any]
+}
+
 /**
  * :: DeveloperApi ::
  */
 @DeveloperApi
-case class SetCommandPhysical(key: Option[String], value: Option[String], output: Seq[Attribute])
-                             (@transient context: SQLContext) extends LeafNode {
-  def execute(): RDD[Row] = (key, value) match {
-    // Set value for key k; the action itself would
-    // have been performed in QueryExecution eagerly.
-    case (Some(k), Some(v)) => context.emptyResult
+case class SetCommandPhysical(
+    key: Option[String], value: Option[String], output: Seq[Attribute])(
+    @transient context: SQLContext)
+  extends LeafNode with PhysicalCommand {
+
+  override protected[sql] lazy val sideEffectResult: Seq[(String, String)] = (key, value) match {
+    // Set value for key k.
+    case (Some(k), Some(v)) =>
+      context.set(k, v)
+      Array.empty[(String, String)]
+
     // Query the value bound to key k.
-    case (Some(k), None) =>
-      val resultString = context.getOption(k) match {
-        case Some(v) => s"$k=$v"
-        case None => s"$k is undefined"
-      }
-      context.sparkContext.parallelize(Seq(new GenericRow(Array[Any](resultString))), 1)
+    case (Some(k), _) =>
+      Array(k -> context.getOption(k).getOrElse("<undefined>"))
+
     // Query all key-value pairs that are set in the SQLConf of the context.
     case (None, None) =>
-      val pairs = context.getAll
-      val rows = pairs.map { case (k, v) =>
-        new GenericRow(Array[Any](s"$k=$v"))
-      }.toSeq
-      // Assume config parameters can fit into one split (machine) ;)
-      context.sparkContext.parallelize(rows, 1)
-    // The only other case is invalid semantics and is impossible.
-    case _ => context.emptyResult
+      context.getAll
+
+    case _ =>
+      throw new IllegalArgumentException()
   }
+
+  def execute(): RDD[Row] = {
+    val rows = sideEffectResult.map { case (k, v) => new GenericRow(Array[Any](k, v)) }
+    context.sparkContext.parallelize(rows, 1)
+  }
+
+  override def otherCopyArgs = context :: Nil
 }
 
 /**
  * :: DeveloperApi ::
  */
 @DeveloperApi
-case class ExplainCommandPhysical(child: SparkPlan, output: Seq[Attribute])
-                                 (@transient context: SQLContext) extends UnaryNode {
+case class ExplainCommandPhysical(
+    child: SparkPlan, output: Seq[Attribute])(
+    @transient context: SQLContext)
+  extends UnaryNode with PhysicalCommand {
+
+  // Actually "EXPLAIN" command doesn't cause any side effect.
+  override protected[sql] lazy val sideEffectResult: Seq[String] = this.toString.split("\n")
+
   def execute(): RDD[Row] = {
-    val planString = new GenericRow(Array[Any](child.toString))
-    context.sparkContext.parallelize(Seq(planString))
+    val explanation = sideEffectResult.mkString("\n")
+    context.sparkContext.parallelize(Seq(new GenericRow(Array[Any](explanation))), 1)
   }
 
   override def otherCopyArgs = context :: Nil
@@ -71,18 +95,19 @@ case class ExplainCommandPhysical(child: SparkPlan, output: Seq[Attribute])
  */
 @DeveloperApi
 case class CacheCommandPhysical(tableName: String, doCache: Boolean)(@transient context: SQLContext)
-  extends LeafNode {
+  extends LeafNode with PhysicalCommand {
 
-  lazy val commandSideEffect = {
+  override protected[sql] lazy val sideEffectResult = {
     if (doCache) {
       context.cacheTable(tableName)
     } else {
       context.uncacheTable(tableName)
     }
+    Seq.empty[Any]
   }
 
   override def execute(): RDD[Row] = {
-    commandSideEffect
+    sideEffectResult
     context.emptyResult
   }
 

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -141,7 +141,7 @@ class SQLQuerySuite extends QueryTest {
       sql("SELECT AVG(a),b FROM largeAndSmallInts group by b"),
       Seq((2147483645.0,1),(2.0,2)))
   }
-  
+
   test("count") {
     checkAnswer(
       sql("SELECT COUNT(*) FROM testData2"),
@@ -332,7 +332,7 @@ class SQLQuerySuite extends QueryTest {
         (3, "C"),
         (4, "D")))
   }
-  
+
   test("system function upper()") {
     checkAnswer(
       sql("SELECT n,UPPER(l) FROM lowerCaseData"),
@@ -349,7 +349,7 @@ class SQLQuerySuite extends QueryTest {
         (2, "ABC"),
         (3, null)))
   }
-    
+
   test("system function lower()") {
     checkAnswer(
       sql("SELECT N,LOWER(L) FROM upperCaseData"),
@@ -382,25 +382,25 @@ class SQLQuerySuite extends QueryTest {
     sql(s"SET $testKey=$testVal")
     checkAnswer(
       sql("SET"),
-      Seq(Seq(s"$testKey=$testVal"))
+      Seq(Seq(testKey, testVal))
     )
 
     sql(s"SET ${testKey + testKey}=${testVal + testVal}")
     checkAnswer(
       sql("set"),
       Seq(
-        Seq(s"$testKey=$testVal"),
-        Seq(s"${testKey + testKey}=${testVal + testVal}"))
+        Seq(testKey, testVal),
+        Seq(testKey + testKey, testVal + testVal))
     )
 
     // "set key"
     checkAnswer(
       sql(s"SET $testKey"),
-      Seq(Seq(s"$testKey=$testVal"))
+      Seq(Seq(testKey, testVal))
     )
     checkAnswer(
       sql(s"SET $nonexistentKey"),
-      Seq(Seq(s"$nonexistentKey is undefined"))
+      Seq(Seq(nonexistentKey, "<undefined>"))
     )
     clear()
   }