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From "Jason Lowe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4665) Asynch submit can lose application submissions
Date Tue, 02 Feb 2016 18:48:39 GMT

    [ https://issues.apache.org/jira/browse/YARN-4665?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15128768#comment-15128768

Jason Lowe commented on YARN-4665:

As Rohith points out, I believe the intent of YARN-514 is to handle this mostly on the client
side.  Technically until the application gets into the ACCEPTED state (or later) the submission
process has not completed, and the YARN client code will not return back to the application
until that has completed.  Failures besides ApplicationNotFoundException should be automatically
retried by the retry proxy later, and the code snippet above should handle the case where
the new RM doesn't understand the application being queried because it failed to make it into
the state store.

Could you elaborate one or more specific scenarios that aren't handled properly?  I'm curious
to know the sequence of events that occurs during the failover that makes the user code believe
the application submission was successful (i.e.: the YARN client submit code returned successfully
to the caller), and how that same error doesn't occur if the call was made synchronous.

> Asynch submit can lose application submissions
> ----------------------------------------------
>                 Key: YARN-4665
>                 URL: https://issues.apache.org/jira/browse/YARN-4665
>             Project: Hadoop YARN
>          Issue Type: Bug
>    Affects Versions: 2.1.0-beta
>            Reporter: Daniel Templeton
>            Assignee: Daniel Templeton
> The change introduced in YARN-514 opens up a hole into which applications can fall and
be lost.  Prior to YARN-514, the {{submitApplication()}} call did not complete until the application
state was persisted to the state store.  After YARN-514, the {{submitApplication()}} call
is asynchronous, with the application state being saved later.
> If the state store is slow or unresponsive, it may be that an application's state may
not be persisted for quite a while.  During that time, if the RM fails (over), all applications
that have not yet been persisted to the state store will be lost.  If the active RM loses
ZK connectivity, a significant number of job submissions can pile up before the ZK connection
times out, resulting in a large pile of client failures when it finally does.
> This issue is inherent in the design of YARN-514.  I see three solutions:
> 1. Add a WAL to the state store. HBase does it, so we know how to do it. It seems like
a heavy solution to the original problem, however.  It's certainly not a trivial change.
> 2. Revert YARN-514 and update the RPC layer to allow a connection to be parked if it's
doing something that may take a while. This is a generally useful feature but could be a deep
rabbit hole.
> 3. Revert YARN-514 and add back-pressure to the job submission. For example, we set a
maximum number of threads that can simultaneously be assigned to handle job submissions. 
When that threshold is reached, new job submissions get a try-again-later response. This is
also a generally useful feature and should be a fairly constrained set of changes.
> I think the third option is the most approachable.  It's the smallest change, and it
adds useful behavior beyond solving the original issue.

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