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https://issues.apache.org/jira/browse/SPARK-37099?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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zhengruifeng updated SPARK-37099:
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Attachment: q67.png
q67_optimized.png
> Impl a rank-based filter to optimize top-k computation
> ------------------------------------------------------
>
> Key: SPARK-37099
> URL: https://issues.apache.org/jira/browse/SPARK-37099
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.3.0
> Reporter: zhengruifeng
> Priority: Major
> Attachments: q67.png, q67_optimized.png, skewed_window.png
>
>
> in JD, we found that more than 90% usage of window function follows this
> pattern:
> {code:java}
> select (... (row_number|rank|dense_rank) () over( [partition by ...] order
> by ... ) as rn)
> where rn (==|<|<=) k and other conditions{code}
>
> However, existing physical plan is not optimum:
>
> 1, we should select local top-k records within each partitions, and then
> compute the global top-k. this can help reduce the shuffle amount;
>
> For these three rank functions (row_number|rank|dense_rank), the rank of a
> key computed on partitial dataset is always <= its final rank computed on
> the whole dataset.
> so we can safely discard rows with partitial rank > rn, anywhere.
>
>
> 2, skewed-window: some partition is skewed and take a long time to finish
> computation.
>
> A real-world skewed-window case in our system is attached.
>
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