[jira] [Created] (YARN-366) Add a tracing async dispatcher to simplify debugging

["Sandy Ryza (JIRA)" <ji...@apache.org>]

Sandy Ryza created YARN-366:
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             Summary: Add a tracing async dispatcher to simplify debugging
                 Key: YARN-366
                 URL: https://issues.apache.org/jira/browse/YARN-366
             Project: Hadoop YARN
          Issue Type: New Feature
          Components: nodemanager, resourcemanager
    Affects Versions: 2.0.2-alpha
            Reporter: Sandy Ryza
            Assignee: Sandy Ryza


Exceptions thrown in YARN/MR code with asynchronous event handling do not contain informative stack traces, as all handle() methods sit directly under the dispatcher thread's loop.

This makes errors very difficult to debug for those who are not intimately familiar with the code, as it is difficult to see which chain of events caused a particular outcome.

I propose adding an AsyncDispatcher that instruments events with tracing information.  Whenever an event is dispatched during the handling of another event, the dispatcher would annotate that event with a pointer to its parent.  When the dispatcher catches an exception, it could reconstruct a "stack" trace of the chain of events that led to it, and be able to log something informative.

This would be an experimental feature, off by default, unless extensive testing showed that it did not have a significant performance impact.

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