[GitHub] [spark] cloud-fan commented on a change in pull request #24223: [SPARK-27278][SQL] Optimize GetMapValue when the map is a foldable and the key is not

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cloud-fan commented on a change in pull request #24223: [SPARK-27278][SQL] Optimize GetMapValue when the map is a foldable and the key is not
URL: https://github.com/apache/spark/pull/24223#discussion_r271560401
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ComplexTypes.scala
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 @@ -59,6 +63,16 @@ object SimplifyExtractValueOps extends Rule[LogicalPlan] {
           Literal(null, ga.dataType)
         }
       case GetMapValue(CreateMap(elems), key) => CaseKeyWhen(key, elems)
+      // The case below happens when the map is foldable, but the key is not, so ConstantFolding
+      // converts the map in a Literal, but the GetMapValue is still there since the key is not
+      // foldable. It cannot happen in any other case.
+      case GetMapValue(Literal(map: MapData, MapType(kt, vt, _)), key) if !key.foldable =>
+        val elems = new mutable.ListBuffer[Literal]
+        map.foreach(kt, vt, (key, value) => {
+          elems.append(Literal(key, kt))
+          elems.append(Literal(value, vt))
+        })
+        CaseKeyWhen(key, elems.result())
 
 Review comment:
   Why is `CaseKeyWhen` faster than `GetMapValue`? they both do a linear scan right?

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