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From "Xianyin Xin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-3870) Providing raw container request information for fine scheduling
Date Wed, 30 Dec 2015 07:55:49 GMT

    [ https://issues.apache.org/jira/browse/YARN-3870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15074755#comment-15074755
] 

Xianyin Xin commented on YARN-3870:
-----------------------------------

+1 for adding an unique id for a resource request, but i would suggest we consider these kind
of problems in a more systematic way, considering YARN-314, YARN-1042, YARN-371, YARN-4485
and this.

Like my comment in YARN-314, a natural way the scheduler works should like a factory, it receives
orders, and prepare for that. Once we accept the work philosophy, we'll find it's natural
and necessary for a resource order has the following dimensions
1. order id, which can identify an order, and can get overdue, or has a time limit;
2. priority;
3. a collection of request unit, each specifies a kind of resource request,that should have
a coordinate of <ResourceName/nodeLabels, Capability, NumOfContainers>;
4. relaxLocality;
5. canbeDecomposed, or ifGangScheduling;
6. ...
Scheduler do scheduling based on order form, and should not swallow any information passed
from the app.

Any 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
RM/Scheduler:
> 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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