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https://issues.apache.org/jira/browse/KAFKA-6106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16239115#comment-16239115
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Matthias J. Sax commented on KAFKA-6106:
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I understand your argument about easy to understand configs. A main motivation
to start processing of "ready" tasks is to also allow to query their stores
asap -- currently, we only allow to query stores if the whole {{KafkaStreams}}
instance (or {{StreamsThread}}?) is in state {{RUNNING}} -- long "downtimes"
for IQ is a real issue. But maybe we can also fix this differently -- not 100%
sure if it's related (but it seems to be a requirement to unlock improved IQ
behavior) or orthogonal to this ticket. \cc [~bbejeck] [~damianguy]
> Postpone normal processing of tasks within a thread until restoration of all
> tasks have completed
> -------------------------------------------------------------------------------------------------
>
> Key: KAFKA-6106
> URL: https://issues.apache.org/jira/browse/KAFKA-6106
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 0.11.0.1, 1.0.0
> Reporter: Guozhang Wang
> Assignee: Guozhang Wang
> Priority: Major
>
> Let's say a stream thread hosts multiple tasks, A and B. At the very
> beginning when A and B are assigned to the thread, the thread state is
> {{TASKS_ASSIGNED}}, and the thread start restoring these two tasks during
> this state using the restore consumer while using normal consumer for
> heartbeating.
> If task A's restoration has completed earlier than task B, then the thread
> will start processing A immediately even when it is still in the
> {{TASKS_ASSIGNED}} phase. But processing task A will slow down restoration of
> task B since it is single-thread. So the thread's transition to {{RUNNING}}
> when all of its assigned tasks have completed restoring and now can be
> processed will be delayed.
> Note that the streams instance's state will only transit to {{RUNNING}} when
> all of its threads have transit to {{RUNNING}}, so the instance's transition
> will also be delayed by this scenario.
> We'd better to not start processing ready tasks immediately, but instead
> focus on restoration during the {{TASKS_ASSIGNED}} state to shorten the
> overall time of the instance's state transition.
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