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https://issues.apache.org/jira/browse/KAFKA-8504?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16859341#comment-16859341
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Matthias J. Sax commented on KAFKA-8504:
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While I agree, that it would be better to use a default value for zero for
grace-period, it's not easily possible, due do backward compatibility issues.
Compare the KIP for more details:
[https://cwiki.apache.org/confluence/display/KAFKA/KIP-328%3A+Ability+to+suppress+updates+for+KTables]
In order versions, there was only "retention time" parameter that is set to 1
day by default. To be backward compatible, we need to set grace period to "-1".
For this case, retention-time parameter is interpreted as grace period
(roughly), implying that grace period is effectively 1 day by default.
Hence, if you use suppress() with default values, it won't emit any final
result for 24h. In practices, you would need to set grace-period to a smaller
value, depending on your application requirements.
I was just double checking the docs, and it seems this behavior is actually not
well documents (neither on AK webpage nor in JavaDocs). I think we should
improve the docs accordingly.
> Suppressed do not emit with TimeWindows
> ---------------------------------------
>
> Key: KAFKA-8504
> URL: https://issues.apache.org/jira/browse/KAFKA-8504
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.2.1
> Reporter: Simone
> Priority: Minor
>
> Hi, I'm playing a bit with KafkaStream and the new suppress feature. I
> noticed that when using a {{TimeWindows}} without explicitly setting the
> grace {{suppress}} will not emit any message if used with
> {{Suppressed.untilWindowCloses.}}
> I look a bit into the code and from what I understood with this configuration
> {{suppress}} should use the {{grace}} setting of the {{TimeWindows}}. But
> since using {{TimeWindows.of(Duration)}} default the grace to {{-1}} and when
> getting the grace using the method {{TimeWindows.gracePeriodMs()}} in case of
> grace equals to -1 the return value is set to {{maintainMs() - size()}} I
> think that the end of window is not properly calculated.
> Of course is possible to avoid this problem forcing the {{grace}} to 0 when
> creating the TimeWindows but I think that this should be the default
> behaviour at least when it comes to the suppress feature.
> I hope I have not misunderstood the code in my analysis, thank you :)
> Simone
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