[GitHub] [incubator-druid] litao91 commented on a change in pull request #7791: Fix repeatedly expr parsing in ExpressionPostAggregation

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

litao91 commented on a change in pull request #7791: Fix repeatedly expr parsing in ExpressionPostAggregation
URL: https://github.com/apache/incubator-druid/pull/7791#discussion_r288857622
 
 

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 File path: processing/src/main/java/org/apache/druid/query/aggregation/post/ExpressionPostAggregator.java
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 @@ -100,14 +102,38 @@ private ExpressionPostAggregator(
     this.macroTable = macroTable;
     this.finalizers = finalizers;
 
-    this.parsed = Parser.parse(expression, macroTable);
-    this.dependentFields = ImmutableSet.copyOf(Parser.findRequiredBindings(parsed));
+    this.parsed = Suppliers.memoize(() -> Parser.parse(expression, macroTable));
+    this.dependentFields = Suppliers.memoize(() -> ImmutableSet.copyOf(Parser.findRequiredBindings(parsed.get())));
   }
 
+  private ExpressionPostAggregator(
 
 Review comment:
   Well, I actually deliberately copied the code as Java force the constructor call to be the first statement. So to avoid code copying, I have to introduce one extra constructor, please check which one is preferred. 

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