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From Jay Kreps <...@confluent.io>
Subject Re: [DISCUSSION] adding the serializer api back to the new java producer
Date Tue, 02 Dec 2014 19:09:55 GMT
Hey Joel, you are right, we discussed this, but I think we didn't think
about it as deeply as we should have. I think our take was strongly shaped
by having a wrapper api at LinkedIn that DOES do the serialization
transparently so I think you are thinking of the producer as just an
implementation detail of that wrapper. Imagine a world where every
application at LinkedIn had to figure that part out themselves. That is,
imagine that what you guys supported was just the raw producer api and that
that just handled bytes. I think in that world the types of data you would
see would be totally funky and standardizing correct usage would be a
massive pain.

Conversely, you could imagine advocating the LinkedIn approach where you
just say, well, every org should wrap up the clients in a way that does
things like serialization and other data checks. The problem with that is
that it (1) it is kind of redundant work and it is likely that the wrapper
will goof some nuances of the apis, and (2) it makes documentation and code
sharing really hard. That is, rather than being able to go to a central
place and read how to use the producer, LinkedIn people need to document
the LinkedIn producer wrapper, and users at LinkedIn need to read about
LinkedIn's wrapper for the producer to understand how to use it. Now
imagine this multiplied over every user.

The idea is that since everyone needs to do this we should just make it
easy to package up the best practice and plug it in. That way the
"contract" your application programs to is just the normal producer api.

-Jay

On Tue, Dec 2, 2014 at 10:06 AM, Joel Koshy <jjkoshy.w@gmail.com> wrote:

> Re: pushing complexity of dealing with objects: we're talking about
> just a call to a serialize method to convert the object to a byte
> array right? Or is there more to it? (To me) that seems less
> cumbersome than having to interact with parameterized types. Actually,
> can you explain more clearly what you mean by <q>reason about what
> type of data is being sent</q> in your original email? I have some
> notion of what that means but it is a bit vague and you might have
> meant something else.
>
> Thanks,
>
> Joel
>
> On Tue, Dec 02, 2014 at 09:15:19AM -0800, Jun Rao wrote:
> > Joel,
> >
> > Thanks for the feedback.
> >
> > Yes, the raw bytes interface is simpler than the Generic api. However, it
> > just pushes the complexity of dealing with the objects to the
> application.
> > We also thought about the layered approach. However, this may confuse the
> > users since there is no single entry point and it's not clear which
> layer a
> > user should be using.
> >
> > Jun
> >
> >
> > On Tue, Dec 2, 2014 at 12:34 AM, Joel Koshy <jjkoshy.w@gmail.com> wrote:
> >
> > > > 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.
> > >
> > > Thanks for bringing this up and the patch.  My take on this is that
> > > any reasoning about the data itself is more appropriately handled
> > > outside of the core producer API. FWIW, I don't think this was
> > > _overlooked_ during the initial discussion of the producer API
> > > (especially since it was a significant change from the old producer).
> > > IIRC we believed at the time that there is elegance and flexibility in
> > > a simple API that deals with raw bytes. I think it is more accurate to
> > > say that this is a reversal of opinion for some (which is fine) but
> > > personally I'm still in the old camp :) i.e., I really like the
> > > simplicity of the current 0.8.2 producer API and find parameterized
> > > types/generics to be distracting and annoying; and IMO any
> > > data-specific handling is better absorbed at a higher-level than the
> > > core Kafka APIs - possibly by a (very thin) wrapper producer library.
> > > I don't quite see why it is difficult to share different wrapper
> > > implementations; or even ser-de libraries for that matter that people
> > > can invoke before sending to/reading from Kafka.
> > >
> > > That said I'm not opposed to the change - it's just that I prefer
> > > what's currently there. So I'm +0 on the proposal.
> > >
> > > Thanks,
> > >
> > > Joel
> > >
> > > On Mon, Nov 24, 2014 at 05:58:50PM -0800, 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
> > >
> > >
>
>

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