[jira] [Reopened] (FLINK-8421) HeapInternalTimerService should reconfigure compatible key / namespace serializers on restore

["Tzu-Li (Gordon) Tai (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-8421?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tzu-Li (Gordon) Tai reopened FLINK-8421:
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> HeapInternalTimerService should reconfigure compatible key / namespace serializers on restore
> ---------------------------------------------------------------------------------------------
>
>                 Key: FLINK-8421
>                 URL: https://issues.apache.org/jira/browse/FLINK-8421
>             Project: Flink
>          Issue Type: Bug
>    Affects Versions: 1.4.0, 1.5.0
>            Reporter: Tzu-Li (Gordon) Tai
>            Assignee: Tzu-Li (Gordon) Tai
>            Priority: Blocker
>             Fix For: 1.5.0, 1.4.1, 1.3.4
>
>
> The {{HeapInternalTimerService}} still uses simple {{equals}} checks on restored / newly provided serializers for compatibility checks. This should be replaced with the {{TypeSerializer::ensureCompatibility}} checks instead, so that new serializers can be reconfigured.
> This would entail that the {{TypeSerializerConfiguration}} of the key and namespace serializer in the {{HeapInternalTimerService}} also needs to be written to the raw state.
> For Flink 1.4.0 release and current master, this is a critical bug since the {{KryoSerializer}} has different default base registrations than before due to FLINK-7420. i.e if the key of a window is serialized using the {{KryoSerializer}} in 1.3.x, the restore would never succeed in 1.4.0.
> For 1.3.x, this fix would be an improvement, such that the {{HeapInternalTimerService}} restore will make use of serializer reconfiguration.
> Other remarks:
> * We need to double check all operators that checkpoint / restore from **raw** state. Apparently, the serializer compatibility checks were only implemented for managed state.
> * Migration ITCases apparently do not have enough coverage. A migration test job that uses a key type which required the {{KryoSerializer}}, and uses windows, would have caught this issue.



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