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From Jason Jackson <jasonj...@gmail.com>
Subject Re: Topology is stuck
Date Wed, 09 Apr 2014 21:43:21 GMT
Yah it's probably a bug in trident. It would be amazing if someone figured
out the fix for this. I spent about 6 hours looking into, but couldn't
figure out why it was occuring.

Beyond fixing this, one thing you could do to buy yourself time is disable
batch retries in trident. There's no option for this in the API, but it's
like a 1 or 2 line change to the code. Obviously you loose exactly once
semantics, but at least you would have a system that never falls behind
real-time.



On Wed, Apr 9, 2014 at 1:10 AM, Danijel Schiavuzzi
<danijel@schiavuzzi.com>wrote:

> Thanks Jason. However, I don't think that was the case in my stuck
> topology, otherwise I'd have seen exceptions (thrown by my Trident
> functions) in the worker logs.
>
>
> On Wed, Apr 9, 2014 at 3:02 AM, Jason Jackson <jasonjckn@gmail.com> wrote:
>
>> An example of "corrupted input" that causes a batch to fail would be for
>> example if you expected a schema to your data that you read off kafka, or
>> some queue, and for whatever reason the data didn't conform to your schema
>> and the function that you implement that you pass to stream.each throws an
>> exception when this unexpected situation occurs. This would cause the batch
>> to be retried, but it's deterministically failing, so the batch will be
>> retried forever.
>>
>>
>> On Mon, Apr 7, 2014 at 10:37 AM, Danijel Schiavuzzi <
>> danijel@schiavuzzi.com> wrote:
>>
>>> Hi Jason,
>>>
>>> Could you be more specific -- what do you mean by "corrupted input"?
>>> Do you mean that there's a bug in Trident itself that causes the tuples in
>>> a batch to somehow become corrupted?
>>>
>>> Thanks a lot!
>>>
>>> Danijel
>>>
>>>
>>> On Monday, April 7, 2014, Jason Jackson <jasonjckn@gmail.com> wrote:
>>>
>>>> This could happen if you have corrupted input that always causes a
>>>> batch to fail and be retried.
>>>>
>>>> I have seen this behaviour before and I didn't see corrupted input. It
>>>> might be a bug in trident, I'm not sure. If you figure it out please update
>>>> this thread and/or submit a patch.
>>>>
>>>>
>>>>
>>>> On Mon, Mar 31, 2014 at 7:39 AM, Danijel Schiavuzzi <
>>>> danijel@schiavuzzi.com> wrote:
>>>>
>>>> To (partially) answer my own question -- I still have no idea on the
>>>> cause of the stuck topology, but re-submitting the topology helps -- after
>>>> re-submitting my topology is now running normally.
>>>>
>>>>
>>>> On Wed, Mar 26, 2014 at 6:04 PM, Danijel Schiavuzzi <
>>>> danijel@schiavuzzi.com> wrote:
>>>>
>>>> Also, I did have multiple cases of my IBackingMap workers dying
>>>> (because of RuntimeExceptions) but successfully restarting afterwards (I
>>>> throw RuntimeExceptions in the BackingMap implementation as my strategy in
>>>> rare SQL database deadlock situations to force a worker restart and to
>>>> fail+retry the batch).
>>>>
>>>> From the logs, one such IBackingMap worker death (and subsequent
>>>> restart) resulted in the Kafka spout re-emitting the pending tuple:
>>>>
>>>>     2014-03-22 16:26:43 s.k.t.TridentKafkaEmitter [INFO] re-emitting
>>>> batch, attempt 29698959:736
>>>>
>>>> This is of course the normal behavior of a transactional topology, but
>>>> this is the first time I've encountered a case of a batch retrying
>>>> indefinitely. This is especially suspicious since the topology has been
>>>> running fine for 20 days straight, re-emitting batches and restarting
>>>> IBackingMap workers quite a number of times.
>>>>
>>>> I can see in my IBackingMap backing SQL database that the batch with
>>>> the exact txid value 29698959 has been committed -- but I suspect that
>>>> could come from another BackingMap, since there are two BackingMap
>>>> instances running (paralellismHint 2).
>>>>
>>>> However, I have no idea why the batch is being retried indefinitely now
>>>> nor why it hasn't been successfully acked by Trident.
>>>>
>>>> Any suggestions on the area (topology component) to focus my research
>>>> on?
>>>>
>>>> Thanks,
>>>>
>>>> On Wed, Mar 26, 2014 at 5:32 PM, Danijel Schiavuzzi <
>>>> danijel@schiavuzzi.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I'm having problems with my transactional Trident topology. It has been
>>>> running fine for about 20 days, and suddenly is stuck processing a single
>>>> batch, with no tuples being emitted nor tuples being persisted by the
>>>> TridentState (IBackingMap).
>>>>
>>>> It's a simple topology which consumes messages off a Kafka queue. The
>>>> spout is an instance of storm-kafka-0.8-plus TransactionalTridentKafkaSpout
>>>> and I use the trident-mssql transactional TridentState implementation to
>>>> persistentAggregate() data into a SQL database.
>>>>
>>>> In Zookeeper I can see Storm is re-trying a batch, i.e.
>>>>
>>>>      "/transactional/<myTopologyName>/coordinator/currattempts" is
>>>> "{"29698959":6487}"
>>>>
>>>> ... and the attempt count keeps increasing. It seems the batch with
>>>> txid 29698959 is stuck, as the attempt count in Zookeeper keeps increasing
>>>> -- seems like the batch isn't being acked by Trident and I have no idea
>>>> why, especially since the topology has been running successfully the last
>>>> 20 days.
>>>>
>>>> I did rebalance the topology on one occasion, after which it continued
>>>> running normally. Other than that, no other modifications were done. Storm
>>>> is at version 0.9.0.1.
>>>>
>>>> Any hints on how to debug the stuck topology? Any other useful info I
>>>> might provide?
>>>>
>>>> Thanks,
>>>>
>>>> --
>>>> Danijel Schiavuzzi
>>>>
>>>> E: danijel@schiavuzzi.com
>>>> W: www.schiavuzzi.com
>>>> T: +385989035562
>>>> Skype: danijel.schiavuzzi
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Danijel Schiavuzzi
>>>>
>>>> E: danije
>>>>
>>>>
>>>
>>> --
>>> Danijel Schiavuzzi
>>>
>>> E: danijel@schiavuzzi.com
>>> W: www.schiavuzzi.com
>>> T: +385989035562
>>> Skype: danijels7
>>>
>>
>>
>
>
> --
> Danijel Schiavuzzi
>
> E: danijel@schiavuzzi.com
> W: www.schiavuzzi.com
> T: +385989035562
> Skype: danijels7
>

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