Guozhang Wang created KAFKA-5932:
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Summary: 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
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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