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From Patrick Wendell <pwend...@gmail.com>
Subject Re: Change for submitting to yarn in 1.3.1
Date Thu, 14 May 2015 02:22:16 GMT
Hey Chester,

Thanks for sending this. It's very helpful to have this list.

The reason we made the Client API private was that it was never
intended to be used by third parties programmatically and we don't
intend to support it in its current form as a stable API. We thought
the fact that it was for internal use would be obvious since it
accepts arguments as a string array of CL args. It was always intended
for command line use and the stable API was the command line.

When we migrated the Launcher library we figured we covered most of
the use cases in the off chance someone was using the Client. It
appears we regressed one feature which was a clean way to get the app
ID.

The items you list here 2-6 all seem like new feature requests rather
than a regression caused by us making that API private.

I think the way to move forward is for someone to design a proper
long-term stable API for the things you mentioned here. That could
either be by extension of the Launcher library. Marcelo would be
natural to help with this effort since he was heavily involved in both
YARN support and the launcher. So I'm curious to hear his opinion on
how best to move forward.

I do see how apps that run Spark would benefit of having a control
plane for querying status, both on YARN and elsewhere.

- Patrick

On Wed, May 13, 2015 at 5:44 AM, Chester At Work <chester@alpinenow.com> wrote:
> Patrick
>      There are several things we need, some of them already mentioned in the mailing
list before.
>
> I haven't looked at the SparkLauncher code, but here are few things we need from our
perspectives for Spark Yarn Client
>
>      1) client should not be private ( unless alternative is provided) so we can call
it directly.
>      2) we need a way to stop the running yarn app programmatically ( the PR is already
submitted)
>      3) before we start the spark job, we should have a call back to the application,
which will provide the yarn container capacity (number of cores and max memory ), so spark
program will not set values beyond max values (PR submitted)
>      4) call back could be in form of yarn app listeners, which call back based on yarn
status changes ( start, in progress, failure, complete etc), application can react based on
these events in PR)
>
>      5) yarn client passing arguments to spark program in the form of main program, we
had experience problems when we pass a very large argument due the length limit. For example,
we use json to serialize the argument and encoded, then parse them as argument. For wide columns
datasets, we will run into limit. Therefore, an alternative way of passing additional larger
argument is needed. We are experimenting with passing the args via a established akka messaging
channel.
>
>     6) spark yarn client in yarn-cluster mode right now is essentially a batch job with
no communication once it launched. Need to establish the communication channel so that logs,
errors, status updates, progress bars, execution stages etc can be displayed on the application
side. We added an akka communication channel for this (working on PR ).
>
>        Combined with others items in this list, we are able to redirect print and error
statement to application log (outside of the hadoop cluster), so spark UI equivalent progress
bar via spark listener. We can show yarn progress via yarn app listener before spark started;
and status can be updated during job execution.
>
>     We are also experimenting with long running job with additional spark commands and
interactions via this channel.
>
>
>      Chester
>
>
>
>
>
>
>
>
>
> Sent from my iPad
>
> On May 12, 2015, at 20:54, Patrick Wendell <pwendell@gmail.com> wrote:
>
>> Hey Kevin and Ron,
>>
>> So is the main shortcoming of the launcher library the inability to
>> get an app ID back from YARN? Or are there other issues here that
>> fundamentally regress things for you.
>>
>> It seems like adding a way to get back the appID would be a reasonable
>> addition to the launcher.
>>
>> - Patrick
>>
>> On Tue, May 12, 2015 at 12:51 PM, Marcelo Vanzin <vanzin@cloudera.com> wrote:
>>> On Tue, May 12, 2015 at 11:34 AM, Kevin Markey <kevin.markey@oracle.com>
>>> wrote:
>>>
>>>> I understand that SparkLauncher was supposed to address these issues, but
>>>> it really doesn't.  Yarn already provides indirection and an arm's length
>>>> transaction for starting Spark on a cluster. The launcher introduces yet
>>>> another layer of indirection and dissociates the Yarn Client from the
>>>> application that launches it.
>>>>
>>>
>>> Well, not fully. The launcher was supposed to solve "how to launch a Spark
>>> app programatically", but in the first version nothing was added to
>>> actually gather information about the running app. It's also limited in the
>>> way it works because of Spark's limitations (one context per JVM, etc).
>>>
>>> Still, adding things like this is something that is definitely in the scope
>>> for the launcher library; information such as app id can be useful for the
>>> code launching the app, not just in yarn mode. We just have to find a clean
>>> way to provide that information to the caller.
>>>
>>>
>>>> I am still reading the newest code, and we are still researching options
>>>> to move forward.  If there are alternatives, we'd like to know.
>>>>
>>>>
>>> Super hacky, but if you launch Spark as a child process you could parse the
>>> stderr and get the app ID.
>>>
>>> --
>>> Marcelo
>>
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