Message key as Long in Kafka Streams

Question

I am trying to use Long as type of the message key, but I get

Exception in thread "kafka_stream_app-f236aaca-3f90-469d-9d32-20ff694806ff-StreamThread-1" org.apache.kafka.streams.errors.StreamsException: Failed to deserialize key for record. topic=test, partition=0, offset=0
    at org.apache.kafka.streams.processor.internals.SourceNodeRecordDeserializer.deserialize(SourceNodeRecordDeserializer.java:38)
    at org.apache.kafka.streams.processor.internals.RecordQueue.addRawRecords(RecordQueue.java:84)
    at org.apache.kafka.streams.processor.internals.PartitionGroup.addRawRecords(PartitionGroup.java:117)
    at org.apache.kafka.streams.processor.internals.StreamTask.addRecords(StreamTask.java:474)
    at org.apache.kafka.streams.processor.internals.StreamThread.addRecordsToTasks(StreamThread.java:642)
    at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:548)
    at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:519)
Caused by: org.apache.kafka.common.errors.SerializationException: Size of data received by LongDeserializer is not 8

I checked and the data.length is 7 .

In streamsConfiguration I've set

streamsConfiguration.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.Long().getClass().getName());

and I use

KStream<Long, GenericRecord> stream = builder.stream(topic);

I've tried sending the message via a simple app and also with kafka-avro-console-producer :

/opt/confluent-3.3.0/bin/kafka-avro-console-producer \
--broker-list localhost:9092 \
--topic test \
--property key.separator=, \
--property parse.key=true \
--property key.schema='{"type":"long"}' \
--property value.schema='{"type":"string"}' \
--property schema.registry.url=http://localhost:8081

with message

123,"293"

Using the kafka-avro-console-consumer I can consume the message and see (with --property print.key=true that the key sent is correctly 123 )

Any idea what could be wrong when decoding the message?

Answer 1

Because you are using kafka-avro-console-producer the key is not serialized as plain Long but as an Avro type. Thus, you need to use a corresponding Avro Serde with the same schema you used on the write path (ie, '{"type":"long"}" ).

Also, your return type will not be Long but an Avro type.