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https://issues.apache.org/jira/browse/KAFKA-13678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17497056#comment-17497056
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Matthias J. Sax commented on KAFKA-13678:
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What [~guozhang] says is right – we align stream-time punctuation to the epoch
to ensure they are deterministic. Thus, there is no bug, but what you observe
is by design.
Of course, we can discuss if the current design is ideal or not.
* In your example, we could for example omit the first punctuation (that
technically fires delayed – it's scheduled at 0 but fires at 5) and only
execute the second one
* We could also extend the API to allow users to specify a "time offset", ie,
if you say interval=10 offset=2, we don't schedule as 0,10,20,30, but at
2,12,22,32 etc
> 2nd punctuation using STREAM_TIME does not respect scheduled interval
> ---------------------------------------------------------------------
>
> Key: KAFKA-13678
> URL: https://issues.apache.org/jira/browse/KAFKA-13678
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 3.0.0
> Reporter: Lorenzo Cagnatel
> Priority: Major
>
> Scheduling a punctuator using stream time, the first punctuation occurs
> immediately as documented, but the second one is not triggered at *t_schedule
> + interval* but it could happen before that time.
> For example, assume that we schedule a punctuation every 10 sec at timestamp
> 5 (t5). The system now works like this:
> {noformat}
> t5 -> schedule, punctuate, next schedule at t10
> t6 -> no punctuation
> t7 -> no punctuation
> t8 -> no punctuation
> t9 -> no punctuation
> t10 -> punctuate, next schedule at t20
> ...{noformat}
> In this example the 2nd schedule occurs after 5 seconds from the first one,
> breaking the interval duration.
> From my point of view, a reasonable behaviour could be:
> {noformat}
> t5 -> schedule, punctuate, next schedule at t15
> t6 -> no punctuation
> t7 -> no punctuation
> t8 -> no punctuation
> t9 -> no punctuation
> t10 -> no punctuation
> t11 -> no punctuation
> t12 -> no punctuation
> t13 -> no punctuation
> t14 -> no punctuation
> t15 -> punctuate, next schedule at t25
> ...{noformat}
> The origin of this problem can be found in {*}StreamTask.schedule{*}:
> {code:java}
> /**
> * Schedules a punctuation for the processor
> *
> * @param interval the interval in milliseconds
> * @param type the punctuation type
> * @throws IllegalStateException if the current node is not null
> */
> public Cancellable schedule(final long interval, final PunctuationType type,
> final Punctuator punctuator) {
> switch (type) {
> case STREAM_TIME:
> // align punctuation to 0L, punctuate as soon as we have data
> return schedule(0L, interval, type, punctuator);
> case WALL_CLOCK_TIME:
> // align punctuation to now, punctuate after interval has elapsed
> return schedule(time.milliseconds() + interval, interval, type,
> punctuator);
> default:
> throw new IllegalArgumentException("Unrecognized PunctuationType: "
> + type);
> }
> }{code}
> when, in case of stream time, it calls *schedule* with {*}startTime=0{*}.
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