[jira] [Assigned] (KAFKA-5932) Avoid call fetchPrevious in FlushListeners

["Bill Bejeck (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-5932?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bill Bejeck reassigned KAFKA-5932:
----------------------------------

    Assignee: Bill Bejeck

> Avoid call fetchPrevious in FlushListeners
> ------------------------------------------
>
>                 Key: KAFKA-5932
>                 URL: https://issues.apache.org/jira/browse/KAFKA-5932
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Guozhang Wang
>            Assignee: Bill Bejeck
>
> When caching is turned on for a window or session store, upon {{store.put()}} the cache may gets flushed, trigger the dirty flush listener calling {{maybeForward()}}, which calls {{fetchPrevious()}}.
> Unfortunately {{fetchPrevious()}} could be a very expensive call to make, and sometimes are not necessary:
> 1. When {{KStreamWindowAggregate.process()}} already gets the previous value when aggregating, so we could passing the old value through the tuple forwarder without calling fetchPrevious again.
> 2. When we know that {{sendOldValues}} flag is turned off.



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