[KAFKA-7368] Support joining Windowed KTables

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: streams
• Assignee: Unassigned
• Reporter: John Roesler
• Created: 31/Aug/18 18:29
• Updated: 20/Jun/19 17:23

Description

Currently, there is no good way to join two `KTable<Windowed<K>, V>`, aka windowed KTables.

They are KTable, so they have a `join` operator available, but it currently will use a regular KeyValue store instead of a Windowed store, so it will grow without bound and new windows enter.

One option is to convert both KTables into KStream, and join them (which is a windowed join), and then convert them back into KTables for further processing, but this is an awkward way to accomplish an apparently straightforward task.

It should instead be possible to directly support it, but the trick will be to make it impossible to accidentally use a window store for normal (aka non-windowed) KTables.

Issue Links

• is related to: KAFKA-6556 allow to attach callbacks in kafka streams, to be triggered when a window is expired
• is related to: KAFKA-6840 support windowing in ktable API
• is related to: KAFKA-4212 Add a key-value store that is a TTL persistent cache