Status

Current state: Draft Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]15299 

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

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So if we create KStream from the stream of business events and create a KTable(s) from all database tables that store business entity data (for example using Change Data Capture) we can assemble complete Business Entity using stream-table joins . and then aggregating on event key.

For the Order Completion example above the sequence of order extraction from Kafka topics is as follows:

• As the first step Business event stream could be joined with business entity parent table using stream-table join on PK. Using the order management example on the diagram below this will be Order Processing Events stream joined with Orders KTable on OrderId key resulting in a stream of completed orders. 
• As the second step the stream of completed orders could be left joined with Order Details table using the foreign key (OrderId) resulting in a stream of competed orders with corresponding order details.

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• If order to order details relation 1:n then additional aggregation on OrderId will be required. 

This KIP proposes the new Kafka Streams feature with capability to join the KStream with KTable using left Foreign Key Join

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• There is no impact to existing users because this is a new Interface

Test Plan

Describe in few sentences how the KIP will be tested. We are mostly interested in system tests (since unit-tests are specific to implementation details). How will we know that the implementation works as expected? How will we know nothing broke?

Proposed 

Rejected Alternatives

Proposed new functionality should be tested with the functional test cases to ensure that results of stream-table foreign key join are consistent with results of the standard RDBMS SQL for foreign key left join between two database tables with foreign key relations. The database table that has foreign key field corresponds to the KTable that are on the right of the left join and database table that has a primary key matching foreign key corresponds to the KStream to the left of join.

Rejected Alternatives

NoneIf there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.