The second half of issue Andy Bryant reported in
KAFKA-9390 looks like still exist.
When testing non-key join method without passing in "Named", I noticed that there are schema subjects registered in confluent schema registry without consumer group Id still,
Code in KTableImpl which constructed above naming :
When we have multiple topologies using foreignKey join and registered to same schema registry, we can have a name clash, and fail to register schema.
In order to clean up these schema subjects, we will need to know the internal naming of a consumer group's topology, which is not straightforward and error prone.