Guozhang Wang created KAFKA-6903:
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Summary: Improve KTable's sending old value behavior
Key: KAFKA-6903
URL: https://issues.apache.org/jira/browse/KAFKA-6903
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: Guozhang Wang
Today in KTable's internal implementation, if old values are needed in the down
stream (e.g. if there is an aggregation down stream so that old values need to
be re-send to "subtract" its effects in addition to incorporate the effects of
new values), we will re-compute the old values based on the parent's passed in
old values. This behavior has two issues:
1) re-computing the values again means more cost: for each updated value, they
are computed twice, once as the new value and once as the old value. This
additional cost can ideally be saved.
2) if the computational logic is dependent on some state which could be updated
over time, then calling the same applied function again may actually result in
different values, due to the different state's snapshot.
We should consider how to improve this behavior to avoid the above issues.
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