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Guozhang Wang edited comment on KAFKA-6049 at 10/11/17 12:59 AM: ----------------------------------------------------------------- WIP PR ready at https://github.com/apache/kafka/pull/2975 Needs someone to pick it up, address the left comments, rebase on trunk and push a new PR to continue. was (Author: guozhang): WIP PR ready at https://github.com/apache/kafka/pull/2975#issuecomment-331275009. Needs someone to pick it up, address the left comments, rebase on trunk and push a new PR to continue. > Kafka Streams: Add Cogroup in the DSL > ------------------------------------- > > Key: KAFKA-6049 > URL: https://issues.apache.org/jira/browse/KAFKA-6049 > Project: Kafka > Issue Type: New Feature > Components: streams > Reporter: Guozhang Wang > Labels: api, needs-kip, user-experience > > When multiple streams aggregate together to form a single larger object (eg. > A shopping website may have a cart stream, a wish list stream, and a > purchases stream. Together they make up a Customer.), it is very difficult to > accommodate this in the Kafka-Streams DSL. It generally requires you to group > and aggregate all of the streams to KTables then make multiple outerjoin > calls to end up with a KTable with your desired object. This will create a > state store for each stream and a long chain of ValueJoiners that each new > record must go through to get to the final object. > Creating a cogroup method where you use a single state store will: > Reduce the number of gets from state stores. With the multiple joins when a > new value comes into any of the streams a chain reaction happens where > ValueGetters keep calling ValueGetters until we have accessed all state > stores. > Slight performance increase. As described above all ValueGetters are called > also causing all ValueJoiners to be called forcing a recalculation of the > current joined value of all other streams, impacting performance. -- This message was sent by Atlassian JIRA (v6.4.14#64029)