Lei Guo created YARN-3870:

             Summary: Providing raw container request information for fine 
                 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 
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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