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https://issues.apache.org/jira/browse/SPARK-42931?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17705252#comment-17705252
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ASF GitHub Bot commented on SPARK-42931:
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User 'HeartSaVioR' has created a pull request for this issue:
https://github.com/apache/spark/pull/40561
> dropDuplicates within watermark
> -------------------------------
>
> Key: SPARK-42931
> URL: https://issues.apache.org/jira/browse/SPARK-42931
> Project: Spark
> Issue Type: New Feature
> Components: Structured Streaming
> Affects Versions: 3.5.0
> Reporter: Jungtaek Lim
> Priority: Major
> Attachments: [External] Mini design doc_ dropDuplicates within
> watermark.pdf
>
>
> We got many reports that dropDuplicates does not clean up the state even
> though they have set a watermark for the query. We document the behavior
> clearly that the event time column should be a part of the subset columns for
> deduplication to clean up the state, but it cannot be applied to the
> customers as timestamps are not exactly the same for duplicated events in
> their use cases.
> We propose to deduce a new API of dropDuplicates which has following
> different characteristics compared to existing dropDuplicates:
> * Weaker constraints on the subset (key)
> ** Does not require an event time column on the subset.
> * Looser semantics on deduplication
> ** Only guarantee to deduplicate events within the watermark.
> Since the new API leverages event time, the new API has following new
> requirements:
> * The input must be streaming DataFrame.
> * The watermark must be defined.
> * The event time column must be defined in the input DataFrame.
> More specifically on the semantic, once the operator processes the first
> arrived event, events arriving within the watermark for the first event will
> be deduplicated.
> (Technically, the expiration time should be the “event time of the first
> arrived event + watermark delay threshold”, to match up with future events.)
> Users are encouraged to set the delay threshold of watermark longer than max
> timestamp differences among duplicated events. (If they are unsure, they can
> alternatively set the delay threshold large enough, e.g. 48 hours.)
> Longer design doc will be attached.
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