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Guozhang Wang commented on KAFKA-13197: --------------------------------------- Thanks for filing this [~twbecker]. The current doc says "If {@code keyValueMapper} returns {@code null} implying no match exists, no output record will be added to the resulting {@code KStream}." But I read the tickets and I think you are right: this property is not very reasonable since users may want to know if a single stream record does not find any matching results as well. I think the reasonable behavior (and the java doc should be updated accordingly) in KAFKA-10277 should be {code} If the keyValueMapper returns null implying no matching key found, the ValueJoiner would still be triggered with (null, v, null). {code} Does that sound right to you? > KStream-GlobalKTable join semantics don't match documentation > ------------------------------------------------------------- > > Key: KAFKA-13197 > URL: https://issues.apache.org/jira/browse/KAFKA-13197 > Project: Kafka > Issue Type: Bug > Affects Versions: 2.7.0 > Reporter: Tommy Becker > Priority: Major > > As part of KAFKA-10277, the behavior of KStream-GlobalKTable joins was > changed. It appears the change was intended to merely relax a requirement but > it actually broke backwards compatibility. Although it does allow {{null}} > keys and values in the KStream to be joined, it now excludes {{null}} results > of the {{KeyValueMapper}}. We have an application which can return {{null}} > from the {{KeyValueMapper}} for non-null keys in the KStream, and relies on > these nulls being passed to the {{ValueJoiner}}. Indeed the javadoc still > explicitly says this is done: > {quote}If a KStream input record key or value is null the record will not be > included in the join operation and thus no output record will be added to the > resulting KStream. > If keyValueMapper returns null implying no match exists, a null value will > be provided to ValueJoiner. > {quote} > Both these statements are incorrect. > I think the new behavior is worse than the previous/documented behavior. It > feels more reasonable to have a non-null stream record map to a null join key > (our use-case is event-enhancement where the incoming record doesn't have the > join field), than the reverse. -- This message was sent by Atlassian Jira (v8.3.4#803005)