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https://issues.apache.org/jira/browse/KAFKA-3514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15897413#comment-15897413
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Michal Borowiecki commented on KAFKA-3514:
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Thank you for responding.
Just now I had a thought about the semantics of event time.
It is already possible to provide a TimestampExtractor that determines what the
event time is, given a message.
It's not far fetched to assume user should also want a way to specify what the
event time is, given the absence of messages (on one or more input partitions).
Possibly by providing an implementation other than what
PartitionGroup.timestamp() is doing based on the timestamps of its partitions.
> Stream timestamp computation needs some further thoughts
> --------------------------------------------------------
>
> Key: KAFKA-3514
> URL: https://issues.apache.org/jira/browse/KAFKA-3514
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Guozhang Wang
> Assignee: Eno Thereska
> Labels: architecture
> Fix For: 0.11.0.0
>
>
> Our current stream task's timestamp is used for punctuate function as well as
> selecting which stream to process next (i.e. best effort stream
> synchronization). And it is defined as the smallest timestamp over all
> partitions in the task's partition group. This results in two unintuitive
> corner cases:
> 1) observing a late arrived record would keep that stream's timestamp low for
> a period of time, and hence keep being process until that late record. For
> example take two partitions within the same task annotated by their
> timestamps:
> {code}
> Stream A: 5, 6, 7, 8, 9, 1, 10
> {code}
> {code}
> Stream B: 2, 3, 4, 5
> {code}
> The late arrived record with timestamp "1" will cause stream A to be selected
> continuously in the thread loop, i.e. messages with timestamp 5, 6, 7, 8, 9
> until the record itself is dequeued and processed, then stream B will be
> selected starting with timestamp 2.
> 2) an empty buffered partition will cause its timestamp to be not advanced,
> and hence the task timestamp as well since it is the smallest among all
> partitions. This may not be a severe problem compared with 1) above though.
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