[KAFKA-16644] FK join emits duplicate tombstone on left-side delete

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 3.7.0
• Component/s: streams
• Assignee: Unassigned
• Reporter: Matthias J. Sax
• Created: 30/Apr/24 02:54
• Updated: 01/May/24 05:28
• Resolved: 01/May/24 05:28

Description

We introduced a regression bug in 3.7.0 release via KAFKA-14748. When a left-hand side record is deleted, the join now emits two tombstone records instead of one.

The problem was not detected via unit test, because the tests use a `Map` instead of a `List` when verifying the result topic records (https://github.com/apache/kafka/blob/trunk/streams/src/test/java/org/apache/kafka/streams/integration/KTableKTableForeignKeyJoinIntegrationTest.java#L250-L255).

We should update all test cases to use `List` when reading from the output topic, and of course fix the introduced bug: The `SubscriptionSendProcessorSupplier` is sending two subscription records instead of just a single one: https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/kstream/internals/foreignkeyjoin/SubscriptionSendProcessorSupplier.java#L133-L136

 

Issue Links

• duplicates: KAFKA-16394 ForeignKey LEFT join propagates null value on foreignKey change