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From Joel Koshy <jjkosh...@gmail.com>
Subject Re: [DISCUSSION] adding the serializer api back to the new java producer
Date Tue, 02 Dec 2014 19:53:51 GMT
Thanks for the follow-up Jay.  I still don't quite see the issue here
but maybe I just need to process this a bit more. To me "packaging up
the best practice and plug it in" seems to be to expose a simple
low-level API and give people the option to plug in a (possibly
shared) standard serializer in their application configs (or a custom
one if they choose) and invoke that from code. The additional
serialization call is a minor drawback but a very clear and easily
understood step that can be documented.  The serializer can obviously
also do other things such as schema registration. I'm actually not (or
at least I think I'm not) influenced very much by LinkedIn's wrapper.
It's just that I think it is reasonable to expect that in practice
most organizations (big and small) tend to have at least some specific
organization-specific detail that warrants a custom serializer anyway;
and it's going to be easier to override a serializer than an entire
producer API.

Joel

On Tue, Dec 02, 2014 at 11:09:55AM -0800, Jay Kreps wrote:
> 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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