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https://issues.apache.org/jira/browse/JAMES-3478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17248490#comment-17248490
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Benoit Tellier commented on JAMES-3478:
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This sounds really complicated to me.
Do you have an exemple of two tasks we can not safely launch in parallel?
> [Distributed Task Manager] Run tasks in parallel
> ------------------------------------------------
>
> Key: JAMES-3478
> URL: https://issues.apache.org/jira/browse/JAMES-3478
> Project: James Server
> Issue Type: Improvement
> Components: task
> Reporter: Raphael Ouazana
> Priority: Major
>
> Architecture Decision Record
> Run tasks in parallel
> Status
> draft
> Context
> Historically the task manager has been sequential with only one task running
> at the same time.
> We would like to take advantage of running a distributed task manager to run
> some tasks in parallel on different nodes.
> But we should be able to avoid running some tasks in parallel with some
> others.
> The execution should stay sequential on a single node.
> Decision
> Use a non exclusive queue with prefetchCount=1 in RabbitMQ this way each node
> will prefetch only one message
> Each task will have a Set of resources needed to be acquired.
> It will not be allowed to run in parallel with another task requiring one of
> those resources.
> Those resources could be hierarchical for example :
> cassandra/mailboxes
> cassandra/mailboxes/foo
> A new event Dispatched is created during after a Create Command if the
> resources needed by the task are free. And the task is sent to the workqueue.
> At the termination of a task, we check for Created but not Delivered tasks
> and deliver and send them to the workqueue if they do not depend on locked
> resources now.
> Consequences
> We will have to modify the behavior of the start command to accept a task
> only if no incompatible tasks are already running on the cluster.
> we will have to be wary of detecting stuck task ( in case in a node restart)
> as it should prevent to start new tasks requiring the same resources.
> Definition of done
> Have a test ensuring that given two task managers when 2 tasks which could
> run concurrently are submitted then one is executed on one instance and the
> other on the other instance.
> Have a test ensuring that given two task managers when 2 tasks which could
> NOT run concurrently are submitted then one is executed on an instance and
> the other is executed only once the first one is terminated.
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