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https://issues.apache.org/jira/browse/KAFKA-9501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sophie Blee-Goldman reassigned KAFKA-9501:
------------------------------------------

    Assignee: Sophie Blee-Goldman

> Promote Standby tasks to active tasks without closing them
> ----------------------------------------------------------
>
>                 Key: KAFKA-9501
>                 URL: https://issues.apache.org/jira/browse/KAFKA-9501
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Sophie Blee-Goldman
>            Priority: Critical
>
> The purpose of StandbyTasks in Kafka Streams is fast failover. However, atm 
> we close StandbyTasks (and create a new active task) if they are promoted to 
> active.
> While this works ok for persistent state stores, it renders hot standbys for 
> in-memory state stores useless, because we drop the in-memory state when we 
> close the StandbyTask and thus the new active tasks needs to reread the 
> changelog topic to recreate the in-memory state.
> Hence, we should promote StandbyTasks to active tasks without closing them. 
> This will not only fix the issue for in-memory stores, but will make 
> rebalancing faster for persistent state stores, too, because closing and 
> reopening RocksDB has significant overhead.



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