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https://issues.apache.org/jira/browse/KAFKA-5932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16185655#comment-16185655
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ASF GitHub Bot commented on KAFKA-5932:
---------------------------------------
Github user asfgit closed the pull request at:
https://github.com/apache/kafka/pull/3978
> 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
> Fix For: 1.0.0
>
>
> 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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