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https://issues.apache.org/jira/browse/KAFKA-10137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17168521#comment-17168521
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Bruno Cadonna commented on KAFKA-10137:
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I also noticed this the last time I looked at
{{ChangeLoggingWindowBytesStore}}. Since the sequence number is not incremented
if {{retainDuplicates}} is false, I think it is OK from a correctness point of
view.
Maybe the reason why we write the sequence number also when
{{retainDuplicates}} is false is that in such a way we do not need to
distinguish whether the key has a sequence number or not when we read the keys
again.
> Clean-up retain Duplicate logic in Window Stores
> ------------------------------------------------
>
> Key: KAFKA-10137
> URL: https://issues.apache.org/jira/browse/KAFKA-10137
> Project: Kafka
> Issue Type: Task
> Components: streams
> Affects Versions: 2.5.0
> Reporter: Bruno Cadonna
> Priority: Minor
>
> Stream-stream joins use the regular `WindowStore` implementation but with
> `retainDuplicates` set to true. To allow for duplicates while using the same
> unique-key underlying stores we just wrap the key with an incrementing
> sequence number before inserting it.
> The logic to maintain and append the sequence number is present in multiple
> locations, namely in the changelogging window store and in its underlying
> window stores. We should consolidate this code to one single location.
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