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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5202) Dynamic Overcommit of Node Resources - POC
Date Thu, 09 Jun 2016 15:40:21 GMT

    [ https://issues.apache.org/jira/browse/YARN-5202?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15322717#comment-15322717

Jason Lowe commented on YARN-5202:

We're fine with some of the work being moved into that effort.  We're just posting the proof
of concept prototype we've been running to stimulate discussion around overcommit and have
people try it out if they're interested in what the POC does.  The only reason we didn't go
with YARN-1011 directly is that we needed something that could be implemented quickly and
transparently to applications in the short-term.  It doesn't use the concept of guaranteed
vs. opportunisitc containers but rather simply scales the cluster dynamically node-by-node
and lets the scheduler divvy up the extra capacity based on its existing queue configs.  It
does mean containers can be shot that weren't being shot before, so SLA-critical apps could
be impacted.  That's why we think ultimately a guaranteed vs. opportunistic approach like
YARN-1011 is a better long-term solution.

As for specific parts that could be moved, I agree the UI/metrics stuff would be useful, as
well as the fast-path for updating a node's resources in the scheduler.  As I mentioned in
YARN-5215, it's very expensive to adjust a node's resources in the scheduler with the traditional
approach, so if we can end up doing it dynamically on every node heartbeat it's critical to
make sure that's as cheap as possible.  The nodemanager "self-preservation" preemption logic
is probably also very relevant.  It would need to be updated to add the guaranteed vs. opportunistic
container distinction, but otherwise seems close to what we would want there.

> Dynamic Overcommit of Node Resources - POC
> ------------------------------------------
>                 Key: YARN-5202
>                 URL: https://issues.apache.org/jira/browse/YARN-5202
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: nodemanager, resourcemanager
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Nathan Roberts
>            Assignee: Nathan Roberts
>         Attachments: YARN-5202.patch
> This Jira is to present a proof-of-concept implementation (collaboration between [~jlowe]
and myself) of a dynamic over-commit implementation in YARN.  The type of over-commit implemented
in this jira is similar to but not as full-featured as what's being implemented via YARN-1011.
YARN-1011 is where we see ourselves heading but we needed something quick and completely transparent
so that we could test it at scale with our varying workloads (mainly MapReduce, Spark, and
Tez). Doing so has shed some light on how much additional capacity we can achieve with over-commit
approaches, and has fleshed out some of the problems these approaches will face.
> Primary design goals:
> - Avoid changing protocols, application frameworks, or core scheduler logic,  - simply
adjust individual nodes' available resources based on current node utilization and then let
scheduler do what it normally does
> - Over-commit slowly, pull back aggressively - If things are looking good and there is
demand, slowly add resource. If memory starts to look over-utilized, aggressively reduce the
amount of over-commit.
> - Make sure the nodes protect themselves - i.e. if memory utilization on a node gets
too high, preempt something - preferably something from a preemptable queue
> A patch against trunk will be attached shortly.  Some notes on the patch:
> - This feature was originally developed against something akin to 2.7.  Since the patch
is mainly to explain the approach, we didn't do any sort of testing against trunk except for
basic build and basic unit tests
> - The key pieces of functionality are in {{SchedulerNode}}, {{AbstractYarnScheduler}},
and {{NodeResourceMonitorImpl}}. The remainder of the patch is mainly UI, Config, Metrics,
Tests, and some minor code duplication (e.g. to optimize node resource changes we treat an
over-commit resource change differently than an updateNodeResource change - i.e. remove_node/add_node
is just too expensive for the frequency of over-commit changes)
> - We only over-commit memory at this point. 

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