srowen commented on a change in pull request #23976: [SPARK-27057][SQL] Common
trait for limit exec operators
URL: https://github.com/apache/spark/pull/23976#discussion_r263012586
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/limit.scala
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@@ -27,13 +27,21 @@ import org.apache.spark.sql.catalyst.util.truncatedString
import org.apache.spark.sql.execution.exchange.ShuffleExchangeExec
import org.apache.spark.sql.execution.metric.{SQLShuffleReadMetricsReporter,
SQLShuffleWriteMetricsReporter}
+/**
+ * The operator takes limited number of elements from its child operator.
+ */
+trait LimitExec extends UnaryExecNode {
+ /** Number of element should be taken from child operator */
+ def limit: Int
+}
+
/**
* Take the first `limit` elements and collect them to a single partition.
*
* This operator will be used when a logical `Limit` operation is the final
operator in an
* logical plan, which happens when the user is collecting results back to the
driver.
*/
-case class CollectLimitExec(limit: Int, child: SparkPlan) extends
UnaryExecNode {
+case class CollectLimitExec(limit: Int, child: SparkPlan) extends LimitExec {
Review comment:
I'm not 100% sure how Scala works here, but is `limit: Int` going to
implement `def limit: Int` in the trait? I assume so or else this won't
compile, so OK.
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