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https://issues.apache.org/jira/browse/SAMZA-906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15212507#comment-15212507
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Navina Ramesh commented on SAMZA-906:
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[~jmakes] Left one comment in the RB. Otherwise, looks good!
> Host Affinity - Minimize task reassignment when container count changes
> -----------------------------------------------------------------------
>
> Key: SAMZA-906
> URL: https://issues.apache.org/jira/browse/SAMZA-906
> Project: Samza
> Issue Type: Bug
> Reporter: Jake Maes
> Assignee: Jake Maes
> Fix For: 0.10.1
>
> Attachments: SAMZA-906.patch, SAMZA-906_2.patch, SAMZA-906_3.patch,
> SAMZA-906_3.patch, SAMZA-906_4.patch
>
>
> When the job container count changes the default taskname grouper
> (GroupByContainerCount) will reassign all the tasks among the new container
> list in a round-robin fashion. This causes many of the tasks to shift to new
> containers. The shifted tasks will be unable to restore state from local disk
> because the new containers may not be assigned to the same host that the
> task's original container was assigned to.
> This ticket is to implement a task-to-container affinity, which complements
> the container-to-host affinity in the current implementation. The
> implementation will include a mapping which is persisted to the coordinator
> stream and is used as the basis for the new task-to-container mapping
> (ContainerModel).
> If the container count doesn't change, the old task mapping will be used.
> (Note that this will allow tools to inject custom mappings by writing to the
> coordinator stream).
> If the container count changes, a minimal number of tasks will be reassigned
> from the persisted mapping, in order to "balance" the containers.
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