[jira] [Commented] (JAMES-3478) [Distributed Task Manager] Run tasks in parallel

["Benoit Tellier (Jira)" <se...@james.apache.org>]

    [ https://issues.apache.org/jira/browse/JAMES-3478?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17248490#comment-17248490 ] 

Benoit Tellier commented on JAMES-3478:
---------------------------------------

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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