Kafka: All messages failing in stream while data in topics - apache-kafka

Question

I have topic post_users_tand while use PRINT command on it I get
rowtime: 4/2/20 2:03:48 PM UTC, key: <null>, value: {"userid": 6, "id": 8, "title": "testest", "body": "Testingmoreand more"}
rowtime: 4/2/20 2:03:48 PM UTC, key: <null>, value: {"userid": 7, "id": 11, "title": "testest", "body": "Testingmoreand more"}
So then I create a stream out of this with:
CREATE STREAM userstream (userid INT, id INT, title VARCHAR, body VARCHAR)
WITH (KAFKA_TOPIC='post_users_t',
VALUE_FORMAT='JSON');
But I cant select anything from it and when I DESCRIBE EXTENDED it all the messages have failed.
consumer-messages-per-sec: 1.06 consumer-total-bytes: 116643 consumer-total-messages: 3417 last-message: 2020-04-02T14:08:08.546Z
consumer-failed-messages: 3417 consumer-failed-messages-per-sec: 1.06 last-failed: 2020-04-02T14:08:08.56Z
What am I doing wrong here?
Extra info under!
Print topic from beginning:
ksql> print 'post_users_t' from beginning limit 2;
Key format: SESSION(AVRO) or HOPPING(AVRO) or TUMBLING(AVRO) or AVRO or SESSION(PROTOBUF) or HOPPING(PROTOBUF) or TUMBLING(PROTOBUF) or PROTOBUF or SESSION(JSON) or HOPPING(JSON) or TUMBLING(JSON) or JSON or SESSION(JSON_SR) or HOPPING(JSON_SR) or TUMBLING(JSON_SR) or JSON_SR or SESSION(KAFKA_INT) or HOPPING(KAFKA_INT) or TUMBLING(KAFKA_INT) or KAFKA_INT or SESSION(KAFKA_BIGINT) or HOPPING(KAFKA_BIGINT) or TUMBLING(KAFKA_BIGINT) or KAFKA_BIGINT or SESSION(KAFKA_DOUBLE) or HOPPING(KAFKA_DOUBLE) or TUMBLING(KAFKA_DOUBLE) or KAFKA_DOUBLE or SESSION(KAFKA_STRING) or HOPPING(KAFKA_STRING) or TUMBLING(KAFKA_STRING) or KAFKA_STRING
Value format: AVRO or KAFKA_STRING
rowtime: 4/2/20 1:04:08 PM UTC, key: <null>, value: {"userid": 1, "id": 1, "title": "loremit", "body": "loremit heiluu ja paukkuu"}
rowtime: 4/2/20 1:04:08 PM UTC, key: <null>, value: {"userid": 2, "id": 2, "title": "lorbe", "body": "larboloilllaaa"}

Answer 1

Per the output from ksqlDB's inspection of the topic, your data is serialised in Avro:
Value format: AVRO or KAFKA_STRING
but you have created the STREAM specifying VALUE_FORMAT='JSON'. This will result in deserialisation errors which if you run docker-compose logs -f ksqldb-server you'll see being written out when you try to query the stream.
Since you're using Avro, you don't need to specify the schema. Try this instead:
CREATE STREAM userstream
WITH (KAFKA_TOPIC='post_users_t',
VALUE_FORMAT='AVRO');