[GitHub] [spark] zhengruifeng commented on a change in pull request #33893: [SPARK-36638][SQL] Generalize OptimizeSkewedJoin

Mon, 14 Feb 2022 00:52:16 -0800 


zhengruifeng commented on a change in pull request #33893:
URL: https://github.com/apache/spark/pull/33893#discussion_r805618329



##########
File path: 
sql/core/src/test/scala/org/apache/spark/sql/execution/adaptive/AdaptiveQueryExecSuite.scala
##########
@@ -2476,11 +2703,10 @@ class AdaptiveQueryExecSuite
             "UNION ALL SELECT key2 FROM skewData2 GROUP BY key2", 1, 1)
 
         // skewJoin1 union (skewJoin2 join aggregate)
-        // skewJoin2 will lead to extra shuffles, but skew1 cannot be optimized
          checkSkewJoin(
           "SELECT key1 FROM skewData1 JOIN skewData2 ON key1 = key2 UNION ALL 
" +
             "SELECT key1 from (SELECT key1 FROM skewData1 JOIN skewData2 ON 
key1 = key2) tmp1 " +
-            "JOIN (SELECT key2 FROM skewData2 GROUP BY key2) tmp2 ON key1 = 
key2", 3, 0)
+            "JOIN (SELECT key2 FROM skewData2 GROUP BY key2) tmp2 ON key1 = 
key2", 3, 3)

Review comment:
       this newly added skew test case can be optimized by this PR without 
extra shuffle:
   
   Master | this PR
   --- | ---
   
![master_skew_case](https://user-images.githubusercontent.com/7322292/153830682-e83ac367-a4d6-4bcf-8699-bd5a944f70e2.png)
 | 
![general_skew_case](https://user-images.githubusercontent.com/7322292/153830711-bb7d1bdf-e59e-400d-a79d-a1e61c9ec8e5.png)
   
   
   




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