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From "Yufei Gu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-7655) avoid AM preemption caused by RRs for specific nodes or racks
Date Thu, 11 Jan 2018 23:01:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-7655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16323164#comment-16323164

Yufei Gu commented on YARN-7655:

Thanks [~Steven Rand] for filing this. It makes sense to me to lose some locality to avoid
massive AM container preemption. The likelihood of preemption AM containers to get locality
should be fairly low, but it is obviously high in your cluster ("double-digit occurrences").
Could you provide any insight for that? What are the cluster size and available resources
for each node?

> avoid AM preemption caused by RRs for specific nodes or racks
> -------------------------------------------------------------
>                 Key: YARN-7655
>                 URL: https://issues.apache.org/jira/browse/YARN-7655
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: fairscheduler
>    Affects Versions: 3.0.0
>            Reporter: Steven Rand
>            Assignee: Steven Rand
>         Attachments: YARN-7655-001.patch
> We frequently see AM preemptions when {{starvedApp.getStarvedResourceRequests()}} in
{{FSPreemptionThread#identifyContainersToPreempt}} includes one or more RRs that request containers
on a specific node. Since this causes us to only consider one node to preempt containers on,
the really good work that was done in YARN-5830 doesn't save us from AM preemption. Even though
there might be multiple nodes on which we could preempt enough non-AM containers to satisfy
the app's starvation, we often wind up preempting one or more AM containers on the single
node that we're considering.
> A proposed solution is that if we're going to preempt one or more AM containers for an
RR that specifies a node or rack, then we should instead expand the search space to consider
all nodes. That way we take advantage of YARN-5830, and only preempt AMs if there's no alternative.
I've attached a patch with an initial implementation of this. We've been running it on a few
clusters, and have seen AM preemptions drop from double-digit occurrences on many days to
> Of course, the tradeoff is some loss of locality, since the starved app is less likely
to be allocated resources at the most specific locality level that it asked for. My opinion
is that this tradeoff is worth it, but interested to hear what others think as well.

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