[jira] [Updated] (KAFKA-9501) Promote Standby tasks to active tasks without closing them

["Sophie Blee-Goldman (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-9501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sophie Blee-Goldman updated KAFKA-9501:
---------------------------------------
    Description: 
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.

  was:
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 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.


> 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
>            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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