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From "Carlo Curino (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1021) Yarn Scheduler Load Simulator
Date Tue, 20 Aug 2013 21:45:54 GMT

    [ https://issues.apache.org/jira/browse/YARN-1021?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13745482#comment-13745482

Carlo Curino commented on YARN-1021:

I might have missed this, but can you check whether the ProportionalCapacityPreemptionPolicy
(running as a monitor) gets invoked correctly when running the simulator with the CapacityScheduler
(and with preemption turned on)?

For the use of Clocks in the RM I think it was pretty consistent (if I remember correctly
from our simulator attempt). Also notice that more than a faster version of time, it is important
to achieve discrete event simulation, as this allows awesome debugging... just accelerating/slowing
down time does not give you that. Please consider this seriously, as I think it would heavily
increase the value of your simulator.

Related to that is  consistent replay (as in fully deterministic). This would be very very
valuable to have. I can see this to be invaluable for debugging, testing, demonstrating features
and corner cases etc. 

Simulating NM/AM is indeed costly, thought it stresses a bunch of other part of the system...
pros and cons... I would suggest you to simply make sure that your architecture/design does
not prevent us later on to broaden the scope of the simulation. 

> Yarn Scheduler Load Simulator
> -----------------------------
>                 Key: YARN-1021
>                 URL: https://issues.apache.org/jira/browse/YARN-1021
>             Project: Hadoop YARN
>          Issue Type: New Feature
>          Components: scheduler
>            Reporter: Wei Yan
>            Assignee: Wei Yan
>         Attachments: YARN-1021-demo.tar.gz, YARN-1021-images.tar.gz, YARN-1021.patch,
YARN-1021.patch, YARN-1021.patch, YARN-1021.patch, YARN-1021.patch, YARN-1021.patch, YARN-1021.patch,
> The Yarn Scheduler is a fertile area of interest with different implementations, e.g.,
Fifo, Capacity and Fair  schedulers. Meanwhile, several optimizations are also made to improve
scheduler performance for different scenarios and workload. Each scheduler algorithm has its
own set of features, and drives scheduling decisions by many factors, such as fairness, capacity
guarantee, resource availability, etc. It is very important to evaluate a scheduler algorithm
very well before we deploy it in a production cluster. Unfortunately, currently it is non-trivial
to evaluate a scheduling algorithm. Evaluating in a real cluster is always time and cost consuming,
and it is also very hard to find a large-enough cluster. Hence, a simulator which can predict
how well a scheduler algorithm for some specific workload would be quite useful.
> We want to build a Scheduler Load Simulator to simulate large-scale Yarn clusters and
application loads in a single machine. This would be invaluable in furthering Yarn by providing
a tool for researchers and developers to prototype new scheduler features and predict their
behavior and performance with reasonable amount of confidence, there-by aiding rapid innovation.
> The simulator will exercise the real Yarn ResourceManager removing the network factor
by simulating NodeManagers and ApplicationMasters via handling and dispatching NM/AMs heartbeat
events from within the same JVM.
> To keep tracking of scheduler behavior and performance, a scheduler wrapper will wrap
the real scheduler.
> The simulator will produce real time metrics while executing, including:
> * Resource usages for whole cluster and each queue, which can be utilized to configure
cluster and queue's capacity.
> * The detailed application execution trace (recorded in relation to simulated time),
which can be analyzed to understand/validate the  scheduler behavior (individual jobs turn
around time, throughput, fairness, capacity guarantee, etc).
> * Several key metrics of scheduler algorithm, such as time cost of each scheduler operation
(allocate, handle, etc), which can be utilized by Hadoop developers to find the code spots
and scalability limits.
> The simulator will provide real time charts showing the behavior of the scheduler and
its performance.
> A short demo is available http://www.youtube.com/watch?v=6thLi8q0qLE, showing how to
use simulator to simulate Fair Scheduler and Capacity Scheduler.

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