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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 Fri, 02 Feb 2018 19:20:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-7655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16350831#comment-16350831

Yufei Gu commented on YARN-7655:

The patch looks good to me generally. Only some nits:
# Add Java doc to method {{identifyContainersToPreempt()}} to indicates that preemption will
try to meet locality first no matter resource request relax on it or not, and there is an
exception for AM containers.
# Solve some style issues in the test class.

> 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
>            Priority: Major
>         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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