org.apache.hadoop.yarn.server.resourcemanager.scheduler.Allocation explanation is wanted!

[Anfernee Xu <an...@gmail.com>]

Hi

I'm reading YARN source code, in particular on RM as I need to implement a
special resource scheduler other than the shipped impl such as  capacity or
fair scheduler, when looking at

.FifoScheduler.allocate(ApplicationAttemptId, List<ResourceRequest>,
List<ContainerId>, List<String>, List<String>)

it
returns org.apache.hadoop.yarn.server.resourcemanager.scheduler.Allocation,
I would like to know the exact meaning of each field in Allocation, for
example

       final List<Container> containers;

Does it contains the list of potential containers where task or appMaster
will run at? What happens if the list is empty?

Another question is how container assignment is performed in scheduler, I
think there's no container in RM initially before the first application is
started. Is there any sequence diagram to describe the whole flow?



-- 
--Anfernee