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https://issues.apache.org/jira/browse/KAFKA-5398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16049190#comment-16049190
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Benjamin Bargeton commented on KAFKA-5398:
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Actually I continued to dig into Kafka streams, and I'm having the same kind of
issues with operations that triggers an internal re-partitioning.
For example when joining a KStream with a KTable (after a selectKey on the
stream), if the source topic of the KTable was written with a key that is
equals to the key selected for the KStream, but with a different serialization
(in my case a different schema id), the partition distribution will not match,
and thus the join will not work properly.
Am I missing something or is it a real issue?
> Joins on GlobalKTable don't work properly when combined with Avro and the
> Confluent Schema Registry
> ---------------------------------------------------------------------------------------------------
>
> Key: KAFKA-5398
> URL: https://issues.apache.org/jira/browse/KAFKA-5398
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 0.10.2.0, 0.10.2.1
> Environment: Kafka, Avro, Confluent Schema Registry (3.2.1)
> Reporter: Benjamin Bargeton
>
> Joins between a {{KStream}} and {{GlobalKTable}} is not working as expected
> when using the following setup:
> * Use Kafka in combination with the Confluent Schema Registry
> * Feed a topic ({{my-global-topic}}) that will be use as a {{GlobalKTable}}
> input by posting some messages with an Avro {{GenericRecord}} as the key
> (using a traditional {{Producer/ProducerRecord}} for example).
> The dumb avro schema for the exemple:
> {code:javascript}
> {
> "type": "record",
> "name": "AvroKey",
> "namespace": "com.test.key",
> "fields": [
> {
> "name": "anyfield",
> "type": "string"
> }
> ]
> }
> {code}
> * Start a kafka stream process that process messages using this time an Avro
> {{SpecificRecord}} (AvroKey) generated by the Avro compiler for the same
> schema
> {code:java}
> KStream<AnyKey, AnyObject> stream = builder.stream("my-stream-topic");
> GlobalKTable<AvroKey, AnyObject> globalTable =
> builder.globalTable("my-global-topic", "my-global-topic-store");
> stream
> .leftJoin(globalTable, (k, v) -> new
> AvroKey(v.getKeyOfTheGlobalTable()), (v1, v2) -> /*the ValueJoiner*/)
> .print("Result");
> {code}
> Note that the schema generated by Avro for the {{SpecificRecord}} slightly
> differs from the original one because we use String instead of CharSequence
> (Avro config):
> {code:javascript}
> {
> "type": "record",
> "name": "AvroKey",
> "namespace": "com.test.key",
> "fields": [
> {
> "name": "anyfield",
> "type": {
> "type": "string",
> "avro.java.string": "String"
> }
> }
> ]
> }
> {code}
> * Last but not least, the Confluent Schema Registry will use byte 1-4 of the
> Avro serialized object to put the schema id of the schema stored in the
> schema registry.
> http://docs.confluent.io/current/schema-registry/docs/serializer-formatter.html#wire-format
> Now our issue is that when the {{RocksDBStore}} of the {{GlobalKTable}} will
> be initilized, it will use the {{byte[]}} straight from the key.
> https://github.com/apache/kafka/blob/0.10.2.1/streams/src/main/java/org/apache/kafka/streams/processor/internals/GlobalStateManagerImpl.java#L179
> https://github.com/apache/kafka/blob/0.10.2.1/streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBStore.java#L164
> Schemas for producer and stream app differs slightly (but are compatible), so
> they are registred with a different global id.
> Since the id is contained in the binary representation, the lookup will fail
> during the join.
> I didn't test but the issue is probably broader than just this case: if the
> we have an upstream producer that is doing a schema evolution (with backwards
> compatible change), it should lead to the same issue.
> Please note that when using a {{KTable}} instead of {{GlobalKTable}} it works
> fine, because the key is first deserialized and then reserialized using the
> current serdes:
> https://github.com/apache/kafka/blob/0.10.2.1/streams/src/main/java/org/apache/kafka/streams/processor/internals/StreamTask.java#L197
> https://github.com/apache/kafka/blob/0.10.2.1/streams/src/main/java/org/apache/kafka/streams/state/internals/CachingKeyValueStore.java#L198
> To conclude I'm not sure to fully understand yet how all pieces connect
> together for state stores, but I assume that for a {{GlobalKTable}} there
> should also be a derserialization/reserialization for each key before storing
> them in RocksDB (at least to make {{KTable}} and {{GlobalKTable}} beahvior
> coherent).
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