Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/1123#discussion_r13949881
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/commands.scala ---
@@ -71,16 +72,24 @@ case class SetCommand(
}
/**
+ * An explain command for users to see how a command will be executed.
+ *
+ * Note that this command takes in a logical plan, runs the optimizer on
the logical plan
+ * (but do NOT actually execute it).
+ *
* :: DeveloperApi ::
*/
@DeveloperApi
case class ExplainCommand(
- child: SparkPlan, output: Seq[Attribute])(
+ logicalPlan: LogicalPlan, output: Seq[Attribute])(
@transient context: SQLContext)
- extends UnaryNode with Command {
+ extends LeafNode with Command {
- // Actually "EXPLAIN" command doesn't cause any side effect.
- override protected[sql] lazy val sideEffectResult: Seq[String] =
this.toString.split("\n")
+ // Run through the optimizer to generate the physical plan.
+ // This is really side effect free but we follow the infrastructure
anyway...
--- End diff --
I hope so ..... That was an old comment I just rewrote anyway ...
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