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From Jun Rao <jun...@gmail.com>
Subject Re: [DISCUSSION] adding the serializer api back to the new java producer
Date Tue, 02 Dec 2014 22:45:21 GMT
For (1), yes, but it's easier to make a config change than a code change.
If you are using a third party library, one may not be able to make any
code change.

For (2), it's just that if most consumers always do deserialization after
getting the raw bytes, perhaps it would be better to have these two steps
integrated.

Thanks,

Jun

On Tue, Dec 2, 2014 at 2:05 PM, Joel Koshy <jjkoshy.w@gmail.com> wrote:

> > The issue with a separate ser/deser library is that if it's not part of
> the
> > client API, (1) users may not use it or (2) different users may use it in
> > different ways. For example, you can imagine that two Avro
> implementations
> > have different ways of instantiation (since it's not enforced by the
> client
> > API). This makes sharing such kind of libraries harder.
>
> That is true - but that is also the point I think and it seems
> irrelevant to whether it is built-in to the producer's config or
> plugged in outside at the application-level. i.e., users will not use
> a common implementation if it does not fit their requirements. If a
> well-designed, full-featured and correctly implemented avro-or-other
> serializer/deserializer is made available there is no reason why that
> cannot be shared by different applications.
>
> > As for reason about the data types, take an example of the consumer
> > application. It needs to deal with objects at some point. So the earlier
> > that type information is revealed, the clearer it is to the application.
>
> Again for this, the only additional step is a call to deserialize. At
> some level the application _has_ to deal with the specific data type
> and it is thus reasonable to require that a consumed byte array needs
> to be deserialized to that type before being used.
>
> I suppose I don't see much benefit in pushing this into the core API
> of the producer at the expense of making these changes to the API.  At
> the same time, I should be clear that I don't think the proposal is in
> any way unreasonable which is why I'm definitely not opposed to it,
> but I'm also not convinced that it is necessary.
>
> Thanks,
>
> Joel
>
> >
> > 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
> > > > >
> > > > >
> > >
> > >
>
> --
> Joel
>

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