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https://issues.apache.org/jira/browse/FLINK-19896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17225815#comment-17225815
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Jun Zhang commented on FLINK-19896:
-----------------------------------
We introduce a lightweight variant of AppendOnlyTopNFunction to handle
first-n-row fetching, which only store a counter in the state to record the
occurrence of partition key.
> Improve first-n-rows fetching in the rank 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
> Reporter: Jun Zhang
> Priority: Major
> Attachments: flink-19896.patch
>
>
> 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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