State store partitioned iterator?

Question

I have a Kafka-streams transformer which functions like a windower: it accumulates state into a state store in transform() and then forwards it in an output topic during punctuate(), with the state store topic partition key the same as the input topic. During punctuate(), I would like each StreamThread to only iterate its own partition of the state store to minimize the amount of data to be read from the backing kafka topic. But the only iterator I can get is through

org.apache.kafka.streams.state.ReadOnlyKeyValueStore<K,V>.all()

which iterates through the whole state store.

Is there any way to "assign partitions" of a state store and make punctuate() iterate only on the assigned partitions?

Answer 1

I guess, ReadOnlyKeyValueStore<K,V>.all() does what you want. Note, that the overall state is sharded into multiple stores with one shard/store per partitions. all() does not iterate through "other shards". "all" means "everything local", ie, everything from the shard of a single partition.