[GitHub] [spark] wangyum commented on a change in pull request #34291: [SPARK-37020][SQL] DS V2 LIMIT push down

[GitBox <gi...@apache.org>]

wangyum commented on a change in pull request #34291:
URL: https://github.com/apache/spark/pull/34291#discussion_r732411354



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDown.scala
##########
@@ -225,6 +225,30 @@ object V2ScanRelationPushDown extends Rule[LogicalPlan] with PredicateHelper {
       withProjection
   }
 
+  def applyLimit(plan: LogicalPlan): LogicalPlan = plan.transform {
+    case globalLimit @ GlobalLimit(_,
+        LocalLimit(limitExpr, DataSourceV2ScanRelation(_, scan, _))) =>
+      val supportsPushDownLimit = scan match {
+        case _: SupportsPushDownLimit => true
+        case v1: V1ScanWrapper =>
+          v1.v1Scan match {
+            case _: SupportsPushDownLimit => true
+            case _ => false
+          }
+        case _ => false
+      }
+      if (supportsPushDownLimit) {
+        assert(limitExpr.isInstanceOf[Literal] &&
+          limitExpr.asInstanceOf[Literal].value.isInstanceOf[Integer],
+          "Limit has to be an Integer")
+        val value = limitExpr.asInstanceOf[Literal].value.asInstanceOf[Integer]
+        PushDownUtils.pushLimit(scan, value)
+        globalLimit
+      } else {
+        globalLimit
+      }

Review comment:
       Could we avoid using `assert` here?
   ```scala
       case globalLimit @ Limit(IntegerLiteral(limitValue), DataSourceV2ScanRelation(_, scan, _)) =>
         val supportsPushDownLimit = scan match {
           case _: SupportsPushDownLimit => true
           case v1: V1ScanWrapper =>
             v1.v1Scan match {
               case _: SupportsPushDownLimit => true
               case _ => false
             }
           case _ => false
         }
         if (supportsPushDownLimit) {
           PushDownUtils.pushLimit(scan, limitValue)
           globalLimit
         } else {
           globalLimit
         }
   ```




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