Hello Everyone,
I would very much appreciate if someone could provide me a real world
examplewhere it is more convenient to implement the serializers instead
of just making sure to provide bytearrays.
The code we came up with explicitly avoids the serializer api. I think
it is common understanding that if you want to transport data you need
to have it as a bytearray.
If at all I personally would like to have a serializer interface that
takes the same types as the producer
public interface Serializer<K,V> extends Configurable {
public byte[] serializeKey(K data);
public byte[] serializeValue(V data);
public void close();
}
this would avoid long serialize implementations with branches like
"switch(topic)" or "if(isKey)". Further serializer per topic makes more
sense in my opinion. It feels natural to have a one to one relationship
from types to topics or at least only a few partition per type. But as
we inherit the type from the producer we would have to create many
producers. This would create additional unnecessary connections to the
brokers. With the serializers we create a one type to all topics
relationship and the only type that satisfies that is the bytearray or
Object. Am I missing something here? As said in the beginning I would
like to that usecase that really benefits from using the serializers. I
think in theory they sound great but they cause real practical issues
that may lead users to wrong decisions.
-1 for putting the serializers back in.
Looking forward to replies that can show me the benefit of serializes
and especially how the
Type => topic relationship can be handled nicely.
Best
Jan
On 25.11.2014 02:58, Jun Rao wrote:
Hi, Everyone,
I'd like to start a discussion on whether it makes sense to add the
serializer api back to the new java producer. Currently, the new java
producer takes a byte array for both the key and the value. While this api
is simple, it pushes the serialization logic into the application. This
makes it hard to reason about what type of data is being sent to Kafka and
also makes it hard to share an implementation of the serializer. For
example, to support Avro, the serialization logic could be quite involved
since it might need to register the Avro schema in some remote registry and
maintain a schema cache locally, etc. Without a serialization api, it's
impossible to share such an implementation so that people can easily reuse.
We sort of overlooked this implication during the initial discussion of the
producer api.
So, I'd like to propose an api change to the new producer by adding back
the serializer api similar to what we had in the old producer. Specially,
the proposed api changes are the following.
First, we change KafkaProducer to take generic types K and V for the key
and the value, respectively.
public class KafkaProducer<K,V> implements Producer<K,V> {
public Future<RecordMetadata> send(ProducerRecord<K,V> record, Callback
callback);
public Future<RecordMetadata> send(ProducerRecord<K,V> record);
}
Second, we add two new configs, one for the key serializer and another for
the value serializer. Both serializers will default to the byte array
implementation.
public class ProducerConfig extends AbstractConfig {
.define(KEY_SERIALIZER_CLASS_CONFIG, Type.CLASS,
"org.apache.kafka.clients.producer.ByteArraySerializer", Importance.HIGH,
KEY_SERIALIZER_CLASS_DOC)
.define(VALUE_SERIALIZER_CLASS_CONFIG, Type.CLASS,
"org.apache.kafka.clients.producer.ByteArraySerializer", Importance.HIGH,
VALUE_SERIALIZER_CLASS_DOC);
}
Both serializers will implement the following interface.
public interface Serializer<T> extends Configurable {
public byte[] serialize(String topic, T data, boolean isKey);
public void close();
}
This is more or less the same as what's in the old producer. The slight
differences are (1) the serializer now only requires a parameter-less
constructor; (2) the serializer has a configure() and a close() method for
initialization and cleanup, respectively; (3) the serialize() method
additionally takes the topic and an isKey indicator, both of which are
useful for things like schema registration.
The detailed changes are included in KAFKA-1797. For completeness, I also
made the corresponding changes for the new java consumer api as well.
Note that the proposed api changes are incompatible with what's in the
0.8.2 branch. However, if those api changes are beneficial, it's probably
better to include them now in the 0.8.2 release, rather than later.
I'd like to discuss mainly two things in this thread.
1. Do people feel that the proposed api changes are reasonable?
2. Are there any concerns of including the api changes in the 0.8.2 final
release?
Thanks,
Jun
