[GitHub] [spark] wangyum opened a new pull request #31691: [SPARK-34575][SQL] Push down limit through window when partitionSpec is empty

Sun, 28 Feb 2021 21:53:26 -0800 


wangyum opened a new pull request #31691:
URL: https://github.com/apache/spark/pull/31691


   ### What changes were proposed in this pull request?
   
   Push down limit through `Window` when partitionSpec is empty and window 
function is range based. This is a real case from production:
   
   
![image](https://user-images.githubusercontent.com/5399861/109457143-3900c680-7a95-11eb-9078-806b041175c2.png)
   
   
   
   ### Why are the changes needed?
   
   Improve query performance.
   
   ```scala
   spark.range(500000000).selectExpr("id AS a", "id AS 
b").write.saveAsTable("t1")
   spark.sql("SELECT *, ROW_NUMBER() OVER(ORDER BY a) AS rowId FROM t1 LIMIT 
5").show
   ```
   
   Before this pr | After this pr
   -- | --
   
![image](https://user-images.githubusercontent.com/5399861/109456919-c68fe680-7a94-11eb-89ca-67ec03267158.png)
 | 
![image](https://user-images.githubusercontent.com/5399861/109456927-cd1e5e00-7a94-11eb-9866-d76b2665caea.png)
   
   
   
   
   ### Does this PR introduce _any_ user-facing change?
   
   No.
   
   
   ### How was this patch tested?
   
   Unit test.
   


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