Github user marmbrus commented on a diff in the pull request: https://github.com/apache/spark/pull/1071#discussion_r13733500 --- Diff: 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] --- End diff -- Okay, fine to not return OK. Regarding emptyResult that is a bad name, but it is used for things like `SELECT 1`. So, if we fix it to actually be empty we need to create a `singleEmptyRow` RDD for use in those cases.
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