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From "Arun Suresh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-3870) Providing raw container request information for fine scheduling
Date Wed, 23 Dec 2015 06:11:46 GMT

    [ https://issues.apache.org/jira/browse/YARN-3870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15069208#comment-15069208

Arun Suresh commented on YARN-3870:

Thank you for starting this discussion [~grey]

Correct me if I am wrong, what you are proposing, I guess is some way for the Scheduler to
co-relate the expanded Resource Requests. I do feel this would be genuinely useful, not only
from a Scheduling perspective for eg. making affinity / anti-afinity scheduling decisions
viz. YARN-1042. This will also greatly help improving pre-emption decisions in the FairScheduler
viz. YARN-2154.. 

This would also be extremely useful for AMs too. Currently the MRAM does the book keeping
and matches an allocated container to ResourceRequest. AMs can be generally relieved of this
job if an allocated Container Token can easily be matched against a Resource Request.

One possible approach could be to have the AMClient generate a unique id for a Resource request
and tag each of the expanded requests (Node, Rack and ANY) with this id. This Id can then
be passed around in the Container/ContainerTokenIdentifier.

[~kasha@cloudera.com], [~vinodkv], [~leftnoteasy], Thoughts ?

> Providing raw container request information for fine scheduling
> ---------------------------------------------------------------
>                 Key: YARN-3870
>                 URL: https://issues.apache.org/jira/browse/YARN-3870
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: api, applications, capacityscheduler, fairscheduler, resourcemanager,
scheduler, yarn
>            Reporter: Lei Guo
> Currently, when AM sends container requests to RM and scheduler, it expands individual
container requests into host/rack/any format. For instance, if I am asking for container request
with preference "host1, host2, host3", assuming all are in the same rack rack1, instead of
sending one raw container request to RM/Scheduler with raw preference list, it basically expand
it to become 5 different objects with host1, host2, host3, rack1 and any in there. When scheduler
receives information, it basically already lost the raw request. This is ok for single container
request, but it will cause trouble when dealing with multiple container requests from the
same application. Consider this case:
> 6 hosts, two racks:
> rack1 (host1, host2, host3) rack2 (host4, host5, host6)
> When application requests two containers with different data locality preference:
> c1: host1, host2, host4
> c2: host2, host3, host5
> This will end up with following container request list when client sending request to
> host1: 1 instance
> host2: 2 instances
> host3: 1 instance
> host4: 1 instance
> host5: 1 instance
> rack1: 2 instances
> rack2: 2 instances
> any: 2 instances
> Fundamentally, it is hard for scheduler to make a right judgement without knowing the
raw container request. The situation will get worse when dealing with affinity and anti-affinity
or even gang scheduling etc.
> We need some way to provide raw container request information for fine scheduling purpose.

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