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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4616) Kafka consumer doesn't store last emmited watermarks per partition in state
Date Thu, 26 Jan 2017 08:36:24 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15839419#comment-15839419
] 

ASF GitHub Bot commented on FLINK-4616:
---------------------------------------

Github user tzulitai commented on the issue:

    https://github.com/apache/flink/pull/3031
  
    A re-clarification about backwards compatibility for state type change:
    Currently, one limitation for compatible applications across savepoint restore is that
you can't change the type of state otherwise state restore will fail, therefore not compatible.
The only work around, is to have another field as the new state with the new type, and somehow
try to "encode" / "decode" the watermark state into / from the original `Tuple2<KafkaTopicPartition,
Long>`. I don't think this is easily possible ...
    
    At the same time, there was recent discussion about letting the window operators also
checkpoint watermarks. So perhaps we might not need to let the Kafka sources checkpoint watermarks
in the end, if the window operators already take care of restoring the previous event time.
    What I'm curious about right now is whether or not in the future, redistributions of Kafka
partition states across source subtasks will work well with the checkpointed watermarks in
the downstream window operators. I don't think there should be a problem.
    
    @aljoscha can you perhaps help clarify this?


> Kafka consumer doesn't store last emmited watermarks per partition in state
> ---------------------------------------------------------------------------
>
>                 Key: FLINK-4616
>                 URL: https://issues.apache.org/jira/browse/FLINK-4616
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.1.1
>            Reporter: Yuri Makhno
>            Assignee: Roman Maier
>
> Kafka consumers stores in state only kafka offsets and doesn't store last emmited watermarks,
this may go to wrong state when checkpoint is restored:
> Let's say our watermark is (timestamp - 10) and in case we have the following messages
queue results will be different after checkpoint restore and during normal processing:
> A(ts = 30)
> B(ts = 35)
> ------ checkpoint goes here
> C(ts=15) -- this one should be filtered by next time window
> D(ts=60)



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