How to access a KStreams Materialized State Store from another Stream Processor - apache-kafka

Question

I need to be able to remove a record from a Ktable from a separate Stream Processor. Today I'm using aggregate() and passing a materialized state store. In a separate processor that reads from a "termination" topic, I'd like to query that materialized state store either in a .transform() or a different .aggregate() and 'remove' that key/value. Every time I try to access the materialized state from a separate stream processor, it keeps telling me either the store isn't added to the topology, so then I add it and run it again, then it tells me it's already be registered and errors out.
builder.stream("topic1").map().groupByKey().aggregate(() -> null,
(aggKey, newValue, aggValue) -> {
//add to the Ktable
return newValue;
},
stateStoreMaterialized);
and in a separate stream I want to delete a key from that stateStoreMaterialized
builder.stream("topic2")
.transform(stateStoreDeleteTransformer, stateStoreSupplier.name())
stateStoreDeleteTransformer will query the key and delete it.
//in ctor
KeyValueBytesStoreSupplier stateStoreSupplier = Stores.persistentKeyValueStore("store1");
stateStoreMaterialized = Materialized.<String, MyObj>as(stateStoreSupplier)
.withKeySerde(Serdes.String())
.withValueSerde(mySerDe);
I don't have a terminal flag on my topic1 stream object value that can trigger a deletion. It has to come from another stream/topic.
When I try to use the same Materialized Store on two separate stream processors I get..
Invalid topology: Topic STATE_STORE-repartition has already been registered by another source.
at org.springframework.kafka.config.StreamsBuilderFactoryBean.start(StreamsBuilderFactoryBean.java:268)
Edit:
This is the 1st error I receive.
Caused by: org.apache.kafka.streams.errors.StreamsException: Processor KSTREAM-TRANSFORMVALUES-0000000012 has no access to StateStore store1 as the store is not connected to the processor. If you add stores manually via '.addStateStore()' make sure to connect the added store to the processor by providing the processor name to '.addStateStore()' or connect them via '.connectProcessorAndStateStores()'. DSL users need to provide the store name to '.process()', '.transform()', or '.transformValues()' to connect the store to the corresponding operator. If you do not add stores manually, please file a bug report at https://issues.apache.org/jira/projects/KAFKA.
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.getStateStore(ProcessorContextImpl.java:104)
at org.apache.kafka.streams.processor.internals.ForwardingDisabledProcessorContext.getStateStore(ForwardingDisabledProcessorContext.java:85)
So then I do this:
stateStoreSupplier = Stores.persistentKeyValueStore(STATE_STORE_NAME);
storeStoreBuilder = Stores.keyValueStoreBuilder(stateStoreSupplier, Serdes.String(), jsonSerDe);
stateStoreMaterialized = Materialized.as(stateStoreSupplier);
Then I get this error:
Caused by: org.apache.kafka.streams.errors.TopologyException: Invalid topology: StateStore 'state-store' is already added.
at org.apache.kafka.streams.processor.internals.InternalTopologyBuilder.addStateStore(InternalTopologyBuilder.java:520)
at org.apache.kafka.streams.processor.internals.InternalTopologyBuilder.addStateStore(InternalTopologyBuilder.java:512)
Here's the code that fixed my issue. As it turns out, order matters when building the streams. Had to set the materialized store first and then in subsequent lines of code, setup the transformer.
/**
* Create the streams using the KStreams DSL - a method to configure the stream and add any state stores.
*/
#Bean
public KafkaStreamsConfig setup() {
final JsonSerDe<Bus> ltaSerde = new JsonSerDe<>(Bus.class);
final StudentSerde<Student> StudentSerde = new StudentSerde<>();
//start lta stream
KStream<String, Bus> ltaStream = builder
.stream(ltaInputTopic, Consumed.with(Serdes.String(), ltaSerde));
final KStream<String, Student> statusStream = this.builder
.stream(this.locoStatusInputTopic,
Consumed.with(Serdes.String(),
StudentSerde));
//create lta store
KeyValueBytesStoreSupplier ltaStateStoreSupplier = Stores.persistentKeyValueStore(LTA_STATE_STORE_NAME);
final Materialized<String, Bus, KeyValueStore<Bytes, byte[]>> ltaStateStoreMaterialized =
Materialized.
<String, Bus>as(ltaStateStoreSupplier)
.withKeySerde(Serdes.String())
.withValueSerde(ltaSerde);
KTable<String, Bus> ltaStateProcessor = ltaStream
//map and convert lta stream into Loco / LTA key value pairs
.groupByKey(Grouped.with(Serdes.String(), ltaSerde))
.aggregate(
//The 'aggregate' and 'reduce' functions ignore messages with null values FYI.
// so if the value after the groupbykey produces a null value, it won't be removed from the state store.
//which is why it's very important to send a message with some terminal flag indicating this value should be removed from the store.
() -> null, /* initializer */
(aggKey, newValue, aggValue) -> {
if (null != newValue.getAssociationEndTime()) { //if there is an endTime associated to this train/loco then remove it from the ktable
logger.trace("removing LTA: {} loco from {} train", newValue.getLocoId(), newValue.getTrainAuthorization());
return null; //Returning null removes the record from the state store as well as its changelog topic. re: https://objectpartners.com/2019/07/31/slimming-down-your-kafka-streams-data/
}
logger.trace("adding LTA: {} loco from {} train", newValue.getLocoId(), newValue.getTrainAuthorization());
return newValue;
}, /* adder */
ltaStateStoreMaterialized
);
// don't need builder.addStateStore(keyValueStoreStoreBuilder); and CANT use it
// because the ltaStateStoreMaterialized will already be added to the topology in the KTable aggregate method above.
// The below transformer can use the state store because it's already added (apparently) by the aggregate method.
// Add the KTable processors first, then if there are any transformers that need to use the store, add them after the KTable aggregate method.
statusStream.map((k, v) -> new KeyValue<>(v.getLocoId(), v))
.transform(locoStatusTransformerSupplier, ltaStateStoreSupplier.name())
.to("testing.outputtopic", Produced.with(Serdes.String(), StudentSerde));
return this; //can return anything except for void.
}

Answer 1

is stateStoreMaterialized and stateStoreSupplier.name() has the same name?
Use have a error in your topology
KStream.transform(stateStoreDeleteTransformer, stateStoreSupplier.name())
You have to supply new instant of StateStoreDeleteTransformer per ProcessContext in TransformerSupplier, like this:
KStream.transform(StateStoreDeleteTransformer::new, stateStoreSupplier.name())
or
KStream.transform(() -> StateStoreDeleteTransformerSupplier.get(), stateStoreSupplier.name())//StateStoreDeleteTransformerSupplier return new instant of StateStoreDeleteTransformer
in stateStoreDeleteTransformer how do you intent on using stateStoreMaterialized inside transformer directly?
I have the similar use case and I using a KeyValueStore<String, MyObj>
public void init(ProcessorContext context) {
kvStore = (KeyValueStore<String, MyObj>) context.getStateStore("store1");
}