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https://issues.apache.org/jira/browse/FLINK-9107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16419302#comment-16419302
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ASF GitHub Bot commented on FLINK-9107:
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Github user NicoK commented on the issue:
https://github.com/apache/flink/pull/5790
Actually, more advanced schemes using `current watermark + 1` (which fires
with the next watermark) for the event time timer should also go into the
documentation. I'll extend the PR ...
> Document timer coalescing for ProcessFunctions
> ----------------------------------------------
>
> Key: FLINK-9107
> URL: https://issues.apache.org/jira/browse/FLINK-9107
> Project: Flink
> Issue Type: Improvement
> Components: Documentation, Streaming
> Affects Versions: 1.3.0, 1.4.0, 1.5.0, 1.6.0
> Reporter: Nico Kruber
> Assignee: Nico Kruber
> Priority: Major
> Fix For: 1.5.0, 1.4.3, 1.3.4
>
>
> In a {{ProcessFunction}}, registering timers for each event via
> {{ctx.timerService().registerEventTimeTimer()}} using times like
> {{ctx.timestamp() + timeout}} will get a millisecond accuracy and may thus
> create one timer per millisecond which may lead to some overhead in the
> {{TimerService}}.
> This problem can be mitigated by using timer coalescing if the desired
> accuracy of the timer can be larger than 1ms. A timer firing at full seconds
> only, for example, can be realised like this:
> {code}
> coalescedTime = ((ctx.timestamp() + timeout) / 1000) * 1000;
> ctx.timerService().registerEventTimeTimer(coalescedTime);
> {code}
> As a result, only a single timer may exist for every second since we do not
> add timers for timestamps that are already there.
> This should be documented in the {{ProcessFunction}} docs.
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