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From Jiangjie Qin <j...@linkedin.com.INVALID>
Subject Re: [DISCUSSION] adding the serializer api back to the new java producer
Date Thu, 04 Dec 2014 18:33:01 GMT

I'm just thinking instead of binding serialization with producer, another
option is to bind serializer/deserializer with
ProducerRecord/ConsumerRecord (please see the detail proposal below.)
	   The arguments for this option is:
	A. A single producer could send different message types. There are
several use cases in LinkedIn for per record serializer
	- In Samza, there are some in-stream order-sensitive control messages
having different deserializer from other messages.
	- There are use cases which need support for sending both Avro messages
and raw bytes.
	- Some use cases needs to deserialize some Avro messages into generic
record and some other messages into specific record.
	B. In current proposal, the serializer/deserilizer is instantiated
according to config. Compared with that, binding serializer with
ProducerRecord and ConsumerRecord is less error prone.


	This option includes the following changes:
	A. Add serializer and deserializer interfaces to replace serializer
instance from config.
		Public interface Serializer <K, V> {
			public byte[] serializeKey(K key);
			public byte[] serializeValue(V value);
		}
		Public interface deserializer <K, V> {
			Public K deserializeKey(byte[] key);
			public V deserializeValue(byte[] value);
		}

	B. Make ProducerRecord and ConsumerRecord abstract class implementing
Serializer <K, V> and Deserializer <K, V> respectively.
		Public abstract class ProducerRecord <K, V> implements Serializer <K, V>
{...}
		Public abstract class ConsumerRecord <K, V> implements Deserializer <K,
V> {...}

	C. Instead of instantiate the serializer/Deserializer from config, let
concrete ProducerRecord/ConsumerRecord extends the abstract class and
override the serialize/deserialize methods.

		Public class AvroProducerRecord extends ProducerRecord <String,
GenericRecord> {
			...
			@Override
			Public byte[] serializeKey(String key) {Š}
			@Override
			public byte[] serializeValue(GenericRecord value);
		}

		Public class AvroConsumerRecord extends ConsumerRecord <String,
GenericRecord> {
			...
			@Override
			Public K deserializeKey(byte[] key) {Š}
			@Override
			public V deserializeValue(byte[] value);
		}

	D. The producer API changes to
		Public class KafkaProducer {
			...

			Future<RecordMetadata> send (ProducerRecord <K, V> record) {
				...
				K key = record.serializeKey(record.key);
				V value = record.serializedValue(record.value);
				BytesProducerRecord bytesProducerRecord = new
BytesProducerRecord(topic, partition, key, value);
				...
			}
			...
		}



We also had some brainstorm in LinkedIn and here are the feedbacks:

If the community decide to add the serialization back to new producer,
besides current proposal which changes new producer API to be a template,
there are some other options raised during our discussion:
	1) Rather than change current new producer API, we can provide a wrapper
of current new producer (e.g. KafkaSerializedProducer) and make it
available to users. As there is value in the simplicity of current API.
	
	2) If we decide to go with tempalated new producer API, according to
experience in LinkedIn, it might worth considering to instantiate the
serializer in code instead of from config so we can avoid runtime errors
due to dynamic instantiation from config, which is more error prone. If
that is the case, the producer API could be changed to something like:
		producer = new Producer<K, V>(KeySerializer<K>, ValueSerializer<V>)

--Jiangjie (Becket) Qin


On 11/24/14, 5:58 PM, "Jun Rao" <junrao@gmail.com> 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


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