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From "Matthias J. Sax" <matth...@confluent.io>
Subject Re: Fixing two critical bugs in kafka streams
Date Mon, 06 Mar 2017 00:10:34 GMT
Sachin,

thanks a lot for contributing!

Right now, I am not sure if I understand the change. On
CommitFailedException, why can we just resume the thread? To me, it
seems that the thread will be in an invalid state and thus it's not save
to just swallow the exception and keep going. Can you shed some light?

And from my understanding, the deadlock is "caused" by the change from
above, right? So if it is save to swallow the exception, we should do
some "clean up" to avoid the deadlock in the first place, instead of
applying and additional timeout.

Also, if this is a bug, we should have a JIRA.

-Matthias


On 3/5/17 4:11 AM, Sachin Mittal wrote:
> Hi,
> Please find the new PR
> https://github.com/apache/kafka/pull/2642/
> 
> I see that in trunk there has been change which is different from in 10.2.0
> 
> 10.2.0
>        if (firstException.get() == null) {
>             firstException.set(commitOffsets());
>        }
>  vs trunk
>         if (firstException.get() == null) {
>             // TODO: currently commit failures will not be thrown to users
>             // while suspending tasks; this need to be re-visit after KIP-98
>             commitOffsets();
>         }
> I am not sure in view of this is is my part of the fix still valid. Looks
> like it is still valid.
> 
> Also on side note what is the policy of closing a branch that is just
> released.
> 
> Since you have release 10.2.0 we are using that and that is why have made
> changes in that branch so that our changes just modify the needed code and
> we don't mess up the other released code.
> 
> Is the new release released off the branch 10.2.0, if yes then you should
> not close it as there can be patch fixes on them.
> 
> Or is the release always made off the branch trunk. In that case how can we
> pick up the code on which the release binaries were created so when we
> build the binary we have exactly same code as released one, plus any
> changes (we or someone else) makes on it.
> 
> Also if a branch is closed, then perhaps we should delete it or mark it
> closed or something.
> 
> Please let us know how releases get created (off what codebase), so we are
> more exact in applying our changes to.
> 
> Thanks
> Sachin
> 
> 
> 
> On Sun, Mar 5, 2017 at 3:40 PM, Eno Thereska <eno.thereska@gmail.com> wrote:
> 
>> Thanks Sachin, one thing before the review, 0.10.2 is closed now, this
>> needs to target trunk.
>>
>> Thanks
>> Eno
>>> On 5 Mar 2017, at 09:10, Sachin Mittal <sjmittal@gmail.com> wrote:
>>>
>>> Please review the PR and let me know if this makes sense.
>>>
>>> https://github.com/apache/kafka/pull/2640
>>>
>>> Thanks
>>> Sachin
>>>
>>>
>>> On Sun, Mar 5, 2017 at 1:49 PM, Eno Thereska <eno.thereska@gmail.com>
>> wrote:
>>>
>>>> Thanks Sachin for your contribution. Could you create a pull request out
>>>> of the commit (so we can add comments, and also so you are acknowledged
>>>> properly for your contribution)?
>>>>
>>>> Thanks
>>>> Eno
>>>>> On 5 Mar 2017, at 07:34, Sachin Mittal <sjmittal@gmail.com> wrote:
>>>>>
>>>>> Hi,
>>>>> So far in our experiment we have encountered 2 critical bugs.
>>>>> 1. If a thread takes more that MAX_POLL_INTERVAL_MS_CONFIG to compute
a
>>>>> cycle it gets evicted from group and rebalance takes place and it gets
>>>> new
>>>>> assignment.
>>>>> However when this thread tries to commit offsets for the revoked
>>>> partitions
>>>>> in
>>>>> onPartitionsRevoked it will again throw the CommitFailedException.
>>>>>
>>>>> This gets handled by ConsumerCoordinatorso there is no point to assign
>>>> this
>>>>> exception to
>>>>> rebalanceException in StreamThread and stop it. It has already been
>>>>> assigned new partitions and it can continue.
>>>>>
>>>>> So as fix in case on CommitFailedException I am not killing the
>>>> StreamThrea.
>>>>>
>>>>> 2. Next we see a deadlock state when to process a task it takes longer
>>>>> than MAX_POLL_INTERVAL_MS_CONFIG
>>>>> time. Then this threads partitions are assigned to some other thread
>>>>> including rocksdb lock. When it tries to process the next task it
>> cannot
>>>>> get rocks db lock and simply keeps waiting for that lock forever.
>>>>>
>>>>> in retryWithBackoff for AbstractTaskCreator we have a backoffTimeMs =
>>>> 50L.
>>>>> If it does not get lock the we simply increase the time by 10x and keep
>>>>> trying inside the while true loop.
>>>>>
>>>>> We need to have a upper bound for this backoffTimeM. If the time is
>>>> greater
>>>>> than  MAX_POLL_INTERVAL_MS_CONFIG and it still hasn't got the lock
>> means
>>>>> this thread's partitions are moved somewhere else and it may not get
>> the
>>>>> lock again.
>>>>>
>>>>> So I have added an upper bound check in that while loop.
>>>>>
>>>>> The commits are here:
>>>>> https://github.com/sjmittal/kafka/commit/
>> 6f04327c890c58cab9b1ae108af4ce
>>>> 5c4e3b89a1
>>>>>
>>>>> please review and if you feel they make sense, please merge it to main
>>>>> branch.
>>>>>
>>>>> Thanks
>>>>> Sachin
>>>>
>>>>
>>
>>
> 


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