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https://issues.apache.org/jira/browse/FLINK-19896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17223557#comment-17223557
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Jark Wu edited comment on FLINK-19896 at 10/30/20, 10:25 AM:
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I'm not sure about this. If we support first-n-rows for
`DeduplicateKeepFirstRowFunction`, then it breaks the semantic of "Deduplicate".
Besides, if we want to support first-n-rows for
`DeduplicateKeepFirstRowFunction`, the `DeduplicateKeepFirstRowFunction` will
end up to be another top-n (Rank) operator implementation.
I think we should focus on how to improve the performance of Rank operator in
this case.
was (Author: jark):
I'm not sure about this. If we support first-n-rows for
`DeduplicateKeepFirstRowFunction`, then it breaks the semantic of "Deduplicate".
Besides, if we want to support first-n-rows for
`DeduplicateKeepFirstRowFunction`, the `DeduplicateKeepFirstRowFunction` will
end up to be another top-n (Rank) operator implementation.
I think we should focus how to improve the performance of Rank operator in this
case.
> Support first-n-rows deduplication in the Deduplicate operator
> --------------------------------------------------------------
>
> Key: FLINK-19896
> URL: https://issues.apache.org/jira/browse/FLINK-19896
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Planner, Table SQL / Runtime
> Affects Versions: 1.12.0, 1.11.3
> Reporter: Jun Zhang
> Priority: Major
> Fix For: 1.11.2
>
>
> Currently Deduplicate operator only supports first-row deduplication (ordered
> by proc-time). In scenario of first-n-rows deduplication, the planner has to
> resort to Rank operator. However, Rank operator is less efficient than
> Deduplicate due to larger state and more state access.
> This issue proposes to extend DeduplicateKeepFirstRowFunction to support
> first-n-rows deduplication. And the original first-row deduplication would be
> a special case of first-n-rows deduplication.
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