Thomas Graves created YARN-1769:
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Summary: CapacityScheduler: Improve reservations
Key: YARN-1769
URL: https://issues.apache.org/jira/browse/YARN-1769
Project: Hadoop YARN
Issue Type: Improvement
Components: capacityscheduler
Affects Versions: 2.3.0
Reporter: Thomas Graves
Assignee: Thomas Graves
Currently the CapacityScheduler uses reservations in order to handle requests
for large containers and the fact there might not currently be enough space
available on a single host.
The current algorithm for reservations is to reserve as many containers as
currently required and then it will start to reserve more above that after a
certain number of re-reservations (currently biased against larger containers).
Anytime it hits the limit of number reserved it stops looking at any other
nodes. This results in potentially missing nodes that have enough space to
fullfill the request.
The other place for improvement is currently reservations count against your
queue capacity. If you have reservations you could hit the various limits
which would then stop you from looking further at that node.
The above 2 cases can cause an application requesting a larger container to
take a long time to gets it resources.
We could improve upon both of those by simply continuing to look at incoming
nodes to see if we could potentially swap out a reservation for an actual
allocation.
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