[GitHub] ravipesala commented on a change in pull request #3058: [CARBONDATA-3238] Solve StackOverflowError using MV datamap

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ravipesala commented on a change in pull request #3058: [CARBONDATA-3238] Solve StackOverflowError using MV datamap
URL: https://github.com/apache/carbondata/pull/3058#discussion_r247390850
 
 

 ##########
 File path: datamap/mv/core/src/main/scala/org/apache/carbondata/mv/rewrite/DefaultMatchMaker.scala
 ##########
 @@ -677,8 +677,18 @@ object SelectSelectGroupbyChildDelta extends DefaultMatchPattern with PredicateH
               val aliasMap_exp = AttributeMap(
                 gb_2c.outputList.collect {
                   case a: Alias => (a.toAttribute, a) })
+
+              // avoid to transform a expression more than twrice
+              // accept for select and having
+              val transformedExpFlags = scala.collection.mutable.Map[ExprId, Int]()
+              aliasMap_exp.keySet.map(alias =>
+                transformedExpFlags += (alias.exprId -> 0))
               val sel_3q_exp = sel_3q.transformExpressions({
-                case attr: Attribute if aliasMap_exp.contains(attr) => aliasMap_exp(attr)
+                case attr: Attribute if aliasMap_exp.contains(attr) &&
+                  transformedExpFlags(attr.exprId) < 2 => {
+                  transformedExpFlags(attr.exprId) += 1
+                  aliasMap_exp(attr)
+                }
 
 Review comment:
   In this way, we may not able to solve the complete issue as attributes may repeat in input/output list of select plan. Better create a wrapper and do the transform as below.
   
   First create a wrapper class for alias
   ```
   case class AliasWrapper(alias: Alias) extends UnaryExpression {
                   override def child: Expression = null
   
                   override protected def doGenCode(ctx: CodegenContext,
                       ev: ExprCode): ExprCode = ev
   
                   override def dataType: DataType = alias.dataType
                 }
   ```
   And change the code as below.
   ```
    val aliasMap_exp = AttributeMap(
                   gb_2c.outputList.collect {
                     case a: Alias => (a.toAttribute, AliasWrapper(a)) })
                 val sel_3q_exp = sel_3q.transformExpressions({
                   case attr: Attribute if aliasMap_exp.contains(attr) => aliasMap_exp(attr)
                 }).transformExpressions {
                   case AliasWrapper(alias: Alias) => alias
                 }
   ```

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