Sandy Ryza created YARN-371:
-------------------------------
Summary: Consolidate resource requests in AM-RM heartbeat
Key: YARN-371
URL: https://issues.apache.org/jira/browse/YARN-371
Project: Hadoop YARN
Issue Type: Improvement
Components: api, resourcemanager, scheduler
Affects Versions: 2.0.2-alpha
Reporter: Sandy Ryza
Assignee: Sandy Ryza
Each AMRM heartbeat consists of a list of resource requests. Currently, each
resource request consists of a container count, a resource vector, and a
location, which may be a node, a rack, or "*". When an application wishes to
request a task run in multiple localtions, it must issue a request for each
location. This means that for a node-local task, it must issue three requests,
one at the node-level, one at the rack-level, and one with * (any). These
requests are not linked with each other, so when a container is allocated for
one of them, the RM has no way of knowing which others to get rid of. When a
node-local container is allocated, this is handled by decrementing the number
of requests on that node's rack and in *. But when the scheduler allocates a
task with a node-local request on its rack, the request on the node is left
there. This can cause delay-scheduling to try to assign a container on a node
that nobody cares about anymore.
Additionally, unless I am missing something, the current model does not allow
requests for containers only on a specific node or specific rack. While this is
not a use case for MapReduce currently, it is conceivable that it might be
something useful to support in the future, for example to schedule long-running
services that persist state in a particular location, or for applications that
generally care less about latency than data-locality.
Lastly, the ability to understand which requests are for the same task will
possibly allow future schedulers to make more intelligent scheduling decisions,
as well as permit a more exact understanding of request load.
I would propose the tweak of allowing a single ResourceRequest to encapsulate
all the location information for a task. So instead of just a single location,
a ResourceRequest would contain an array of locations, including nodes that it
would be happy with, racks that it would be happy with, and possibly *. Side
effects of this change would be a reduction in the amount of data that needs to
be transferred in a heartbeat, as well in as the RM's memory footprint,
becaused what used to be different requests for the same task are now able to
share some common data.
While this change breaks compatibility, if it is going to happen, it makes
sense to do it now, before YARN becomes beta.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
