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https://issues.apache.org/jira/browse/KAFKA-4219?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Guozhang Wang resolved KAFKA-4219.
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Resolution: Fixed
Fix Version/s: 2.0.0
> Permit setting of event time in stream processor
> ------------------------------------------------
>
> Key: KAFKA-4219
> URL: https://issues.apache.org/jira/browse/KAFKA-4219
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 0.10.0.1
> Reporter: Elias Levy
> Priority: Major
> Labels: api
> Fix For: 2.0.0
>
>
> Event time is assigned in stream sources via {{TimestampExtractor}}. Once
> the event time has been assigned, it remains the same, regardless of any
> downstream processing in the topology. This is insufficient for many
> processing jobs, particularly when the output of the job is written back into
> a Kafka topic, where the record's time is encoded outside of the record's
> value.
> For instance:
> * When performing windowed aggregations it may be desirable for the timestamp
> of the emitted record to be lower or higher limits of the time window, rather
> than the timestamp of the last processed element, which may be anywhere
> within the time window.
> * When joining two streams, it is non-deterministic which of the two record's
> timestamps will be the timestamp of the emitted record. It would be either
> one depending on what order the records are processed. Even where this
> deterministic, it may be desirable for the emitted timestamp to be altogether
> different from the timestamp of the joined records. For instance, setting
> the timestamp to the current processing time may be desirable.
> * In general, lower level processors may wish to set the timestamp of emitted
> records to an arbitrary value.
>
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