Hi Alex,
Thank you for your PR. I agree PAssert is much nicer.
You're right. Despite the source not being executed in parallel, the results of
the source will then be distributed round-robin to all the other tasks. Note
that there is no GroupBy operation. Thanks for spotting the issue.
I think the apparent severity of the issue fixed in your PR was also caused by
the more critical concurrency issue fixed in
https://github.com/apache/beam/pull/7171/files I've run the test several
thousand times since then and didn't see any failures anymore. But that's just
on my machine, PAssert is clearly much safer.
> Please also try to follow this pattern on any other tests which you may have.
You already had me convinced by your arguments before you said this :) I'll
change the remaining tests to use PAssert as well. I'll request a review for it
from you if you don't mind.
I think it would make sense if we synced more timely when we both look into the
same test. Are you on the ASF Slack? Feel free to reach out there for me.
Thanks,
Max
On 05.12.18 21:41, Alex Amato wrote:
I believe that the ParDos are being invoked in parallel. I'm not sure on the
exact semantics, but I believe that beam will execute separate keys on separate
threads, when it processes different bundles for different those keys.
I logged the thread IDs in this test, to verify that different threads are
invoking this code.
Applying my fix, I was able to pass the test 400/400 runs.
I talked to Luke, and he suggested using PAssert, which is the most thread
safe/standard way to verify pipeline results It also simplifies the code a
little bit, removing the last unnecessary DoFn.
PTAL at this PR, I recommend committing this in to remove the concurrency issue
collecting test results and remove flakeyness in this test.
https://github.com/apache/beam/pull/7214/files
Please also try to follow this pattern on any other tests which you may have.
FWIW, Here is the logged thread ids that I saw, I appended logs to a
ConcurrentLinkedQueue and printed them at the end of the test, so this shows the
separate threads and the interleaving of them.
processElement collectResults 26 : 5000 results: 1601591000 threadId:
pool-32-thread-15
processElement collectResults 34 : 4093 results: 1360449464 threadId:
pool-32-thread-14
processElement collectResults 47 : 4093 results: 323962224 threadId:
pool-32-thread-19
processElement collectResults 19 : 4093 results: 323962224 threadId:
pool-32-thread-19
processElement collectResults 45 : 4093 results: 167183883 threadId:
pool-32-thread-18
processElement collectResults 0 : 4093 results: 167183883 threadId:
pool-32-thread-18
processElement collectResults 2 : 4093 results: 167183883 threadId:
pool-32-thread-18
processElement collectResults 30 : 4093 results: 865903006 threadId:
pool-32-thread-21
processElement collectResults 11 : 4093 results: 865903006 threadId:
pool-32-thread-21
processElement collectResults 1 : 4093 results: 865903006 threadId:
pool-32-thread-21
processElement collectResults 41 : 4093 results: 1183940089 threadId:
pool-32-thread-23
processElement collectResults 7 : 4093 results: 1183940089 threadId:
pool-32-thread-23
processElement collectResults 13 : 4093 results: 1183940089 threadId:
pool-32-thread-23
processElement collectResults 36 : 4093 results: 1183940089 threadId:
pool-32-thread-23
processElement collectResults 21 : 4093 results: 907415986 threadId:
pool-32-thread-17
processElement collectResults 32 : 4093 results: 907415986 threadId:
pool-32-thread-17
processElement collectResults 10 : 4093 results: 907415986 threadId:
pool-32-thread-17
processElement collectResults 20 : 4093 results: 907415986 threadId:
pool-32-thread-17
processElement collectResults 14 : 4093 results: 907415986 threadId:
pool-32-thread-17
processElement collectResults 24 : 4093 results: 1391785351 threadId:
pool-32-thread-15
processElement collectResults 46 : 4093 results: 1391785351 threadId:
pool-32-thread-15
processElement collectResults 17 : 4093 results: 1391785351 threadId:
pool-32-thread-15
On Wed, Dec 5, 2018 at 6:49 AM Maximilian Michels <[email protected]
<mailto:[email protected]>> wrote:
Thank you for looking into the test. For me the flakiness was solely caused
by
the non thread-safe GrpcStateService. I have since closed the JIRA issue
because
I didn't see another failure since the fix.
Your fixes are valid, but they won't fix flakiness (if present) in the
current
testing pipeline. Why? The results are only ever written by 1 worker because
the
testing source uses Impulse which generates a signal only received by a
single
worker. So the shared results list is not a problem for this test.
Let me quickly comment on the changes you mentioned:
1) Yes, if we had a parallel source, the List should be a concurrent or
synchronized list.
2) Using a static list should be fine for testing purposes. There are no
other
tests accessing this map. Tests are not run parallel on a class level.
Besides,
there is only one test in this class.
3) If you make the results object transient, then it won't be serialized,
so it
will be 'null' after being deserialized.
Thank you for spending the time to look into the test. Do you think it would
make sense to address changes to the test separately of your PR?
I believe the test can be further improved, e.g. to run more parallel.
Also, if
you see any flakiness after the merged fix, please post the build log in the
JIRA issue.
Thanks,
Max
On 05.12.18 03:18, Alex Amato wrote:
> Well, here is my hacky solution.
> You can see the changes I make to PortableTimersExecutionTest
> https://github.com/apache/beam/pull/6786/files
>
> I don't really understand why the pipeline never starts running when I
make the
> results object transient in PortableTiemrsExecutionTest.
>
> So I instead continue to access a static object, but key it with the test
> parameter, to prevent tests from interfering with each other.
>
> I am not too sure how to proceed. I don't really want to check in this
hacky
> solution. But I am not too sure of what else to do with solved the
problems.
> Please let me know if you have any suggestions.
>
> On Tue, Dec 4, 2018 at 5:26 PM Alex Amato <[email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> Thanks for letting me know Maximillian,
>
> Btw, I've been looking a this test the last few days as well. I have
found a
> few other concurrency issues. That I hope to send a PR out for.
>
> * The PortableTimersExecutionTest result variable is using a static
> ArrayList, but can be writen to concurrently (by multiple thread
AND
> multiple parameterized test instnace) which causing flakeyness.
> * But just using a ConcurrentLinkedQueue and a non static variable
isn't
> sufficient as that will cause a copy of the results object to be
copied
> during doFn serialization. So that makes all the assertions fail,
since
> nothing get written to the same result object the test is using/
> o So it should be made private transient final. However, after
trying
> this I am seeing the test timeout, and I am not sure why.
Continuing
> to debug this.
>
>
> I think that my PR was increasing flakeyness, which is why I saw
more of
> these issues.
> Just wanted to point these out in the meantime, hopefull it helps
with
> debugging for you too.
>
> On Fri, Nov 30, 2018 at 7:49 AM Maximilian Michels <[email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> This turned out to be a tricky bug. Robert and me had a joined
debugging
> session and managed to find the culprit.
>
> PR pending: https://github.com/apache/beam/pull/7171
>
> On 27.11.18 19:35, Kenneth Knowles wrote:
> > I actually didn't look at this one. I filed a bunch more
adjacent flake
> > bugs. I didn't find your bug but I do see that test flaking at
the same
> > time as the others. FWIW here is the list of flakes and
sickbayed tests:
> > https://issues.apache.org/jira/issues/?filter=12343195
> >
> > Kenn
> >
> > On Tue, Nov 27, 2018 at 10:25 AM Alex Amato
<[email protected] <mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>
> > <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>> wrote:
> >
> > +Ken,
> >
> > Did you happen to look into this test? I heard that you
may have
> > been looking into this.
> >
> > On Mon, Nov 26, 2018 at 3:36 PM Maximilian Michels
> <[email protected] <mailto:[email protected]> <mailto:[email protected]
<mailto:[email protected]>>
> > <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>> wrote:
> >
> > Hi Alex,
> >
> > Thanks for your help! I'm quite used to debugging
> > concurrent/distributed
> > problems. But this one is quite tricky, especially
with regards
> > to GRPC
> > threads. I try to provide more information in the
following.
> >
> > There are two observations:
> >
> > 1) The problem is specifically related to how the
cleanup is
> > performed
> > for the EmbeddedEnvironmentFactory. The environment is
shutdown
> > when the
> > SDK Harness exists but the GRPC threads continue to
linger for
> > some time
> > and may stall state processing on the next test.
> >
> > If you do _not_ close DefaultJobBundleFactory, which
happens
> during
> > close() or dispose() in the
FlinkExecutableStageFunction or
> > ExecutableStageDoFnOperator respectively, the tests
run just
> > fine. I ran
> > 1000 test runs without a single failure.
> >
> > The EmbeddedEnvironment uses direct channels which are
marked
> > experimental in GRPC. We may have to convert them to
regular
> socket
> > communication.
> >
> > 2) Try setting a conditional breakpoint in
GrpcStateService
> > which will
> > never break, e.g. "false". Set it here:
> >
>
https://github.com/apache/beam/blob/6da9aa5594f96c0201d497f6dce4797c4984a2fd/runners/java-fn-execution/src/main/java/org/apache/beam/runners/fnexecution/state/GrpcStateService.java#L134
> >
> > The tests will never fail. The SDK harness is always
shutdown
> > correctly
> > at the end of the test.
> >
> > Thanks,
> > Max
> >
> > On 26.11.18 19:15, Alex Amato wrote:
> > > Thanks Maximilian, let me know if you need any
help. Usually
> > I debug
> > > this sort of thing by pausing the IntelliJ debugger
to see
> > all the
> > > different threads which are waiting on various
conditions. If
> > you find
> > > any insights from that, please post them here and
we can try
> > to figure
> > > out the source of the stuckness. Perhaps it may be
some
> > concurrency
> > > issue leading to deadlock?
> > >
> > > On Thu, Nov 22, 2018 at 12:57 PM Maximilian Michels
> > <[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>
> <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>
> > > <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>
> <mailto:[email protected] <mailto:[email protected]>
<mailto:[email protected] <mailto:[email protected]>>>>> wrote:
> > >
> > > I couldn't fix it thus far. The issue does not
seem to be
> > in the Flink
> > > Runner but in the way the tests utilizes the
EMBEDDED
> > environment to
> > > run
> > > multiple portable jobs in a row.
> > >
> > > When it gets stuck it is in RemoteBundle#close
and it is
> > independent of
> > > the test type (batch and streaming have
different
> > implementations).
> > >
> > > Will give it another look tomorrow.
> > >
> > > Thanks,
> > > Max
> > >
> > > On 22.11.18 13:07, Maximilian Michels wrote:
> > > > Hi Alex,
> > > >
> > > > The test seems to have gotten flaky after we
merged
> > support for
> > > portable
> > > > timers in Flink's batch mode.
> > > >
> > > > Looking into this now.
> > > >
> > > > Thanks,
> > > > Max
> > > >
> > > > On 21.11.18 23:56, Alex Amato wrote:
> > > >> Hello, I have noticed
> > > >>
> >
that org.apache.beam.runners.flink.PortableTimersExecutionTest
> > > is very
> > > >> flakey, and repro'd this test timeout on
the master
> > branch in
> > > 40/50 runs.
> > > >>
> > > >> I filed a JIRA issue: BEAM-6111
> > > >>
<https://issues.apache.org/jira/browse/BEAM-6111>. I
> > was just
> > > >> wondering if anyone knew why this may be
occurring,
> > and to check if
> > > >> anyone else has been experiencing this.
> > > >>
> > > >> Thanks,
> > > >> Alex
> > >
> >
>
