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 <[email protected]> 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 <[email protected]> wrote:
>> On Tue, May 12, 2015 at 11:34 AM, Kevin Markey <[email protected]>
>> 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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