[GitHub] [hive] kasakrisz commented on a change in pull request #1096: HIVE-23493: Rewrite plan to join back tables with many projected columns joined multiple times

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

kasakrisz commented on a change in pull request #1096:
URL: https://github.com/apache/hive/pull/1096#discussion_r439922505



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File path: ql/src/java/org/apache/hadoop/hive/ql/parse/CalcitePlanner.java
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@@ -2389,6 +2390,11 @@ private RelNode applyPostJoinOrderingTransform(RelNode basePlan, RelMetadataProv
 
       final HepProgramBuilder program = new HepProgramBuilder();
 
+      if (conf.getBoolVar(ConfVars.HIVE_CARDINALITY_PRESERVING_JOIN_OPTIMIZATION)) {
+        generatePartialProgram(program, false, HepMatchOrder.TOP_DOWN,
+            new HiveCardinalityPreservingJoinRule());

Review comment:
       `HiveCardinalityPreservingJoinRule` is not stateless: it extends `HiveFieldTrimmerRule` which tracks whether it was triggered or not to avoid unnecessary multiple traversals.




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