Hi Lucy, Thanks for the KIP! This is a very much needed update to Kafka Streams. Overall the KIP looks good.
BB1. I have one nit comment with regards to the name. What would you think about `joinByMappedKey / leftJoinByMappedKey` instead? BB2. Since the error condition will continue to exist until we remove the deprecated methods, maybe we could add one line to the Javadoc explicitly stating that readOnlyKey is currently the stream key, not the mapped join key. Thanks, Bill On Tue, May 26, 2026 at 1:19 PM Lucy Liu via dev <[email protected]> wrote: > Hi everyone, > > Gentle ping on this thread. Looking forward to feedback on the KIP! > > Best, > Lucy Liu > > On Fri, May 15, 2026 at 4:19 PM Lucy Liu <[email protected]> wrote: > > > Hello everyone, > > > > I would like to start a discussion on KIP-1340 Pass Join Key to > > `ValueJoinerWithKey` in Streams-GlobalKTable Joins > > < > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-1340%3A+Pass+Join+Key+to+%60ValueJoinerWithKey%60+in+Streams-GlobalKTable+Joins > > > > > > > This proposal aims to introduce joinOnMappedKey and leftJoinOnMappedKey, > > new KStream methods that pass the mapped join key (the result of the > > user-supplied KeyValueMapper) into ValueJoinerWithKey for > > stream-globalTable joins. The existing join/leftJoin overloads pass the > > stream record's key into the joiner instead, contradicting KIP-149's > > contract that readOnlyKey is the join key and silently producing wrong > > values if a joiner intends to read the real join key. The existing > > overloads will be deprecated and removed in a future major release. > > > > Best regards, > > Lucy Liu > > >
