How to be notified about updates to state store of GlobalKTable?

Question

I am using simply API of StreamsBuilder for building a GlobalKTable as this:

Materialized<Long, Category, KeyValueStore<Bytes, byte[]>> materialized =
    Materialized.<Long, Category, KeyValueStore<Bytes, byte[]>>as(this.categoryStoreName)
        .withCachingDisabled()
        .withKeySerde(Serdes.Long())
        .withValueSerde(CATEGORY_JSON_SERDE);

return streamsBuilder.globalTable(categoryTopic, materialized);

I would like to be notified by changes of it. It is rarely updated and in case an update I would like to trigger cache invalidation. What is the Kafka way of doing this?

Answer 1

GlobalKTable does not support this. However, you can use a "global store" and implement your custom Processor that will be called for each update.

Internally, a GlobalKTable uses a "global store" and provides the Processor implementation for you.

You can add a global store via StreamsBuilder#addGlobalStore().