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From Aljoscha Krettek <aljos...@apache.org>
Subject Re: Empty state restore seems to be broken for Kafka source (1.3.2)
Date Thu, 14 Sep 2017 12:46:09 GMT
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.

> 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 <mailto:aljoscha@apache.org>>
>> 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 <mailto:gyfora@apache.org>>
>>> 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 <mailto: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
<mailto: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 <mailto: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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