[KAFKA-15299] Support left stream-table join on foreign key

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: streams
• Labels: kip
• Assignee: Igor Fomenko
• Reporter: Igor Fomenko
• Due: 27/Oct/23
• Created: 02/Aug/23 14:15
• Updated: 02/Aug/23 23:32

Description

KIP-955: https://cwiki.apache.org/confluence/display/KAFKA/KIP-955%3A+Add+stream-table+join+on+foreign+key

Currently in Kafka Streams DSL, KStream to KTable joins could only be performed with the keys. However in practice it is often required to join the messages in Kafka topics using message field as a "foreign key" with the following pattern:  

 
streamX.leftJoin(tableY, RecordTableY::getForegnKey, joiner).to("output-topic-name")
 
The left loin on foreign key operation will result in a stream of messages from two topics joined on foreign key where 0 or more output message is produced for each event on the input stream.