You are viewing a plain text version of this content. The canonical link for it is here.
Posted to issues@spark.apache.org by "Guibin Zhang (Jira)" <ji...@apache.org> on 2021/09/15 22:29:00 UTC
[jira] [Issue Comment Deleted] (SPARK-36770) Improve run-time
performance for window function first and last against UnboundedFollowing
window ROWS frame
[ https://issues.apache.org/jira/browse/SPARK-36770?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Guibin Zhang updated SPARK-36770:
---------------------------------
Comment: was deleted
(was: [https://github.com/apache/spark/pull/34010]
)
> Improve run-time performance for window function first and last against UnboundedFollowing window ROWS frame
> ------------------------------------------------------------------------------------------------------------
>
> Key: SPARK-36770
> URL: https://issues.apache.org/jira/browse/SPARK-36770
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.4.0, 3.1.2
> Reporter: Guibin Zhang
> Priority: Major
>
> *Context*
> The *UnboundedFollowingWindowFunctionFrame* has the time complexity of *O(N^2)*, N is the number of rows in the current partition, more specific the complexity is O(N* (N - 1)/2).
> What happens internally in UnboundedFollowingWindowFunctionFrame:
> In the window frame, while processing each incoming row, it will go through current row till the end of partition to do re-calculation. This process will be repeated on each incoming row, which causes the high run-time complexity.
> But UnboundedPrecedingWindowFunctionFrame has much better time complexity O(N), N is the number of rows in the current partition.
>
> *What is the idea of the improvement?*
> Give the big time complexity difference between UnboundedFollowingWindowFunctionFrame and UnboundedPrecedingWindowFunctionFrame, we can do following conversions to improve the time complexity of first() and last() from O(N^2) to O(N)
> {code:java}
> case 1:
> first() OVER(PARTITION BY colA ORDER BY colB ASC ROWS UNBOUNDED FOLLOWING)
> converts to
> last() OVER(PARTITION BY colA ORDER BY colB DEAC ROWS UNBOUNDED PRECEDING)
> case 2:
> last() OVER(PARTITION BY colA ORDER BY colB ASC ROWS UNBOUNDED FOLLOWING)
> converts to
> first() OVER(PARTITION BY colA ORDER BY colB DESC ROWS UNBOUNDED PRECEDING)
> {code}
>
> *Summary*
> Replace "UNBOUNDED FOLLOWING" with "UNBOUNDED PRECEDING", and flip the ORDER BY for the window functions first() and last() for ROWS.
>
>
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@spark.apache.org
For additional commands, e-mail: issues-help@spark.apache.org