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https://issues.apache.org/jira/browse/KAFKA-8924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17089214#comment-17089214
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Matthias J. Sax commented on KAFKA-8924:
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{quote}there is no sensible default grace period
{quote}
This is of course subjective, but I would be personally fine with a default of
zero. Even if not very common, there are use-cases for which data is actually
ordered (in fact, each time when one uses wall clock time); thus, I don't
consider it "crazy" to use a default of zero.
Furthermore, for simple demos and when people start to build their first apps,
it seem desirable to have a few mandatory parameters as possible to make it
easier to get started?
I see your argument that for a real production use case, one might want to set
a custom grace-period with high probability and thus, I could be convinced to
make it mandatory. It's just a slight preference of mine to use a default of
zero.
What I like most about the proposal is, that we could just fix it in 2.7. We
should have thought about this earlier and should have fix it in the same
release `suppress()` was introduces. Well, better a little delayed than even
more delayed (ie, to 3.0). It would be great to get a KIP for this and get it
into 2.7, release.
> Default grace period (-1) of TimeWindows causes suppress to emit events after
> 24h
> ---------------------------------------------------------------------------------
>
> Key: KAFKA-8924
> URL: https://issues.apache.org/jira/browse/KAFKA-8924
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 2.3.0
> Reporter: Michał
> Assignee: Michał
> Priority: Major
> Labels: needs-kip
>
> h2. Problem
> The default creation of TimeWindows, like
> {code}
> TimeWindows.of(ofMillis(xxx))
> {code}
> calls an internal constructor
> {code}
> return new TimeWindows(sizeMs, sizeMs, -1, DEFAULT_RETENTION_MS);
> {code}
> And the *-1* parameter is the default grace period which I think is here for
> backward compatibility
> {code}
> @SuppressWarnings("deprecation") // continuing to support
> Windows#maintainMs/segmentInterval in fallback mode
> @Override
> public long gracePeriodMs() {
> // NOTE: in the future, when we remove maintainMs,
> // we should default the grace period to 24h to maintain the default
> behavior,
> // or we can default to (24h - size) if you want to be super accurate.
> return graceMs != -1 ? graceMs : maintainMs() - size();
> }
> {code}
> The problem is that if you use a TimeWindows with gracePeriod of *-1*
> together with suppress *untilWindowCloses*, it never emits an event.
> You can check the Suppress tests
> (SuppressScenarioTest.shouldSupportFinalResultsForTimeWindows), where
> [~vvcephei] was (maybe) aware of that and all the scenarios specify the
> gracePeriod.
> I will add a test without it on my branch and it will fail.
> The test:
> https://github.com/atais/kafka/commit/221a04dc40d636ffe93a0ad95dfc6bcad653f4db
>
> h2. Now what can be done
> One easy fix would be to change the default value to 0, which works fine for
> me in my project, however, I am not aware of the impact it would have done
> due to the changes in the *gracePeriodMs* method mentioned before.
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