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https://issues.apache.org/jira/browse/YARN-624?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13735967#comment-13735967
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Carlo Curino commented on YARN-624:
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Related to this is work we just proposed in YARN-1051. We manage dynamically
negotiated reservation of capacity at admission control. The idea is that if I
want gang-scheduling I can declare this at submission time and the system
accept me only if it can "fit" me. At that level we do constraints checking /
knapsack (e.g., that we never promise more gang-style reservations than we can
fit).
This means that at run-time AM-hoarding is ok because we guarantee it to fit.
I am aware of at least 2 limitations of this approach w.r.t. the dynamic
version you were discussing:
* doesn't work if the application doesn't know about its needs until the AM has
started
* we lose large chunks of the cluster (and our previously checked constraints
don't hold)
Neither seems a great concern, and the second one can be handle with
re-planning in the admission-control (which we don't have yet, but its in our
agenda).
> Support gang scheduling in the AM RM protocol
> ---------------------------------------------
>
> Key: YARN-624
> URL: https://issues.apache.org/jira/browse/YARN-624
> Project: Hadoop YARN
> Issue Type: Sub-task
> Components: api, scheduler
> Affects Versions: 2.0.4-alpha
> Reporter: Sandy Ryza
> Assignee: Sandy Ryza
>
> Per discussion on YARN-392 and elsewhere, gang scheduling, in which a
> scheduler runs a set of tasks when they can all be run at the same time,
> would be a useful feature for YARN schedulers to support.
> Currently, AMs can approximate this by holding on to containers until they
> get all the ones they need. However, this lends itself to deadlocks when
> different AMs are waiting on the same containers.
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