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From Gyula Fóra <gyf...@apache.org>
Subject Re: Empty state restore seems to be broken for Kafka source (1.3.2)
Date Thu, 14 Sep 2017 12:53:02 GMT
Good job for figuring this out!
This certainly seems to explain our problems.

Thanks!
Gyula

Aljoscha Krettek <aljoscha@apache.org> ezt írta (időpont: 2017. szept. 14.,
Cs, 14:46):

> After a bit more digging I found that the "isRestored" flag doesn't work
> correctly if there are operators chained to the sink that have state:
> https://issues.apache.org/jira/browse/FLINK-7623
>
> Blocker issue for 1.3.3 and 1.4.0.
>
> Best,
> Aljoscha
>
> On 6. Sep 2017, at 16:05, Aljoscha Krettek <aljoscha@apache.org> wrote:
>
> After discussing this between Stefan and me we think that this should
> actually work.
>
> Do you have the log output from restoring the Kafka Consumer? It would be
> interesting to see whether any of those print:
>  -
> https://github.com/apache/flink/blob/f1a173addd99e5df00921b924352a39810d8d180/flink-connectors/flink-connector-kafka-base/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaConsumerBase.java#L611
>  -
> https://github.com/apache/flink/blob/f1a173addd99e5df00921b924352a39810d8d180/flink-connectors/flink-connector-kafka-base/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaConsumerBase.java#L554
>
> On 6. Sep 2017, at 14:45, Aljoscha Krettek <aljoscha@apache.org> wrote:
>
> Yes, and that's essentially what's happening in the 1.4-SNAPSHOT consumer
> which also has discovery of new partitions. Starting from 1.4-SNAPSHOT we
> store state in a union state, i.e. all sources get all partition on restore
> and if they didn't get any they know that they are new. There is no
> specific logic for detecting this situation, it's just that the partition
> discoverer will be seeded with this information and it will know if it
> discovers a new partition whether it can take ownership of that partition.
>
> I'm sure Gordon (cc'ed) could explain it better than I did.
>
> On 6. Sep 2017, at 14:36, Gyula Fóra <gyfora@apache.org> wrote:
>
> Wouldnt it be enough that Kafka sources store some empty container for
> there state if it is empty, compared to null when it should be bootstrapped
> again?
>
> Gyula
>
> Aljoscha Krettek <aljoscha@apache.org> ezt írta (időpont: 2017. szept.
> 6., Sze, 14:31):
>
>> The problem here is that context.isRestored() is a global flag and not
>> local to each operator. It says "yes this job was restored" but the source
>> would need to know that it is actually brand new and never had any state.
>> This is quite tricky to do, since there is currently no way (if I'm
>> correct) to differentiate between "I got empty state but others maybe got
>> state" and "this source never had state and neither had other parallel
>> instances".
>>
>> Best,
>> Aljoscha
>>
>> On 6. Sep 2017, at 13:56, Stefan Richter <s.richter@data-artisans.com>
>> wrote:
>>
>> Thanks for the report, I will take a look.
>>
>> Am 06.09.2017 um 11:48 schrieb Gyula Fóra <gyfora@apache.org>:
>>
>> Hi all,
>>
>> We are running into some problems with the kafka source after changing
>> the uid and restoring from the savepoint.
>> What we are expecting is to clear the partition state, and set it up all
>> over again, but what seems to happen is that the consumer thinks that it
>> doesnt have any partitions assigned.
>>
>> This was supposed to be fixed in
>> https://github.com/apache/flink/commit/0ecb5d0050b84ba48105836288d43ce4c4749459#diff-06bf4a7f73d98ef91309154654563475
>> but appears to be reworked/reverted in the latest release :
>> https://github.com/apache/flink/blob/0399beed1ea3e04d332b42cc506041d75a6148b4/flink-connectors/flink-connector-kafka-base/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaConsumerBase.java#L547
>>
>> What is the expected behaviour here?
>>
>> Thanks!
>> Gyula
>>
>>
>>
>>
>
>
>

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