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From "Eugene Kirpichov (JIRA)" <j...@apache.org>
Subject [jira] [Created] (BEAM-1784) DataflowPipelineJob.cancel() should be idempotent
Date Thu, 23 Mar 2017 03:09:41 GMT
Eugene Kirpichov created BEAM-1784:
--------------------------------------

             Summary: DataflowPipelineJob.cancel() should be idempotent
                 Key: BEAM-1784
                 URL: https://issues.apache.org/jira/browse/BEAM-1784
             Project: Beam
          Issue Type: Bug
          Components: runner-dataflow
            Reporter: Eugene Kirpichov
            Assignee: Eugene Kirpichov


Right now DataflowPipelineJob.cancel() issues an RPC to the Dataflow service and, if it fails,
checks whether the job is in a terminal state - in that case the failure is ignored.

Ideally, the Dataflow-side cancel call itself would be idempotent, and would succeed even
if the job is already terminated. However, right now this is not the case.

Additionally, Dataflow service can, for a short time, return RUNNING state even for a job
that has already been cancelled (i.e. it will reject cancel() calls, but will report state
as RUNNING).

Because of this, if you call DataflowPipelineJob.cancel() multiple times, it might fail (throw
an exception). Calling cancel() multiple times should, logically, be ok. So, to partially
work around these issues of the Dataflow service, we can make DataflowPipelineJob.cancel()
be idempotent by itself, i.e. absorb duplicate cancel() requests. This, of course, doesn't
address the case when the job terminates externally almost concurrently to calling DataflowPipelineJob.cancel()
- but it's an improvement.



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