[GitHub] [incubator-druid] gianm commented on a change in pull request #9043: sql auto limit wrapping fix

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

gianm commented on a change in pull request #9043: sql auto limit wrapping fix
URL: https://github.com/apache/incubator-druid/pull/9043#discussion_r358366674
 
 

 ##########
 File path: sql/src/main/java/org/apache/druid/sql/calcite/planner/DruidPlanner.java
 ##########
 @@ -258,24 +258,30 @@ private RelNode possiblyWrapRootWithOuterLimitFromContext(
     if (root.rel instanceof Sort) {
       Sort innerSort = (Sort) root.rel;
       final int offset = Calcites.getOffset(innerSort);
+      final int innerLimit = Calcites.getFetch(innerSort);
       final int fetch = Calcites.collapseFetch(
-          Calcites.getFetch(innerSort),
+          innerLimit,
           Ints.checkedCast(outerLimit),
           0
       );
 
+      if (fetch == innerLimit) {
+        // nothing to do, don't bother to make a new sort
+        return root.rel;
+      }
+
+      root.rel.getCluster().getPlanner().setImportance(innerSort, 0.0);
 
 Review comment:
   Setting the importance of a rel to 0 is a way to tell the planner that it should not waste its time considering that rel: i.e., we are confident the new rel is better.

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