Joel,
It's just that if the serializer/deserializer is not part of the API, you
can only encourage people to use it through documentation. However, not
everyone will read the documentation if it's not directly used in the API.
Thanks,
Jun
On Mon, Dec 15, 2014 at 2:11 AM, Joel Koshy <jjkosh...@gmail.com> wrote:
> (sorry about the late follow-up late - I'm traveling most of this
> month)
>
> I'm likely missing something obvious, but I find the following to be a
> somewhat vague point that has been mentioned more than once in this
> thread without a clear explanation. i.e., why is it hard to share a
> serializer/deserializer implementation and just have the clients call
> it before a send/receive? What "usage pattern" cannot be supported by
> the simpler API?
>
> > 1. Can we keep the serialization semantics outside the Producer interface
> > and have simple bytes in / bytes out for the interface (This is what we
> > have today).
> >
> > The points for this is to keep the interface simple and usage easy to
> > understand. The points against this is that it gets hard to share common
> > usage patterns around serialization/message validations for the future.
>
>
> On Tue, Dec 09, 2014 at 03:51:08AM +0000, Sriram Subramanian wrote:
> > Thank you Jay. I agree with the issue that you point w.r.t paired
> > serializers. I also think having mix serialization types is rare. To get
> > the current behavior, one can simply use a ByteArraySerializer. This is
> > best understood by talking with many customers and you seem to have done
> > that. I am convinced about the change.
> >
> > For the rest who gave -1 or 0 for this proposal, does the answers for the
> > three points(updated) below seem reasonable? Are these explanations
> > convincing?
> >
> >
> > 1. Can we keep the serialization semantics outside the Producer interface
> > and have simple bytes in / bytes out for the interface (This is what we
> > have today).
> >
> > The points for this is to keep the interface simple and usage easy to
> > understand. The points against this is that it gets hard to share common
> > usage patterns around serialization/message validations for the future.
> >
> > 2. Can we create a wrapper producer that does the serialization and have
> > different variants of it for different data formats?
> >
> > The points for this is again to keep the main API clean. The points
> > against this is that it duplicates the API, increases the surface area
> and
> > creates redundancy for a minor addition.
> >
> > 3. Do we need to support different data types per record? The current
> > interface (bytes in/bytes out) lets you instantiate one producer and use
> > it to send multiple data formats. There seems to be some valid use cases
> > for this.
> >
> >
> > Mixed serialization types are rare based on interactions with customers.
> > To get the current behavior, one can simply use a ByteArraySerializer.
> >
> > On 12/5/14 5:00 PM, "Jay Kreps" <j...@confluent.io> wrote:
> >
> > >Hey Sriram,
> > >
> > >Thanks! I think this is a very helpful summary.
> > >
> > >Let me try to address your point about passing in the serde at send
> time.
> > >
> > >I think the first objection is really to the paired key/value serializer
> > >interfaces. This leads to kind of a weird combinatorial thing where you
> > >would have an avro/avro serializer a string/avro serializer, a pb/pb
> > >serializer, and a string/pb serializer, and so on. But your proposal
> would
> > >work as well with separate serializers for key and value.
> > >
> > >I think the downside is just the one you call out--that this is a corner
> > >case and you end up with two versions of all the apis to support it.
> This
> > >also makes the serializer api more annoying to implement. I think the
> > >alternative solution to this case and any other we can give people is
> just
> > >configuring ByteArraySerializer which gives you basically the api that
> you
> > >have now with byte arrays. If this is incredibly common then this would
> be
> > >a silly solution, but I guess the belief is that these cases are rare
> and
> > >a
> > >really well implemented avro or json serializer should be 100% of what
> > >most
> > >people need.
> > >
> > >In practice the cases that actually mix serialization types in a single
> > >stream are pretty rare I think just because the consumer then has the
> > >problem of guessing how to deserialize, so most of these will end up
> with
> > >at least some marker or schema id or whatever that tells you how to read
> > >the data. Arguable this mixed serialization with marker is itself a
> > >serializer type and should have a serializer of its own...
> > >
> > >-Jay
> > >
> > >On Fri, Dec 5, 2014 at 3:48 PM, Sriram Subramanian <
> > >srsubraman...@linkedin.com.invalid> wrote:
> > >
> > >> This thread has diverged multiple times now and it would be worth
> > >> summarizing them.
> > >>
> > >> There seems to be the following points of discussion -
> > >>
> > >> 1. Can we keep the serialization semantics outside the Producer
> > >>interface
> > >> and have simple bytes in / bytes out for the interface (This is what
> we
> > >> have today).
> > >>
> > >> The points for this is to keep the interface simple and usage easy to
> > >> understand. The points against this is that it gets hard to share
> common
> > >> usage patterns around serialization/message validations for the
> future.
> > >>
> > >> 2. Can we create a wrapper producer that does the serialization and
> have
> > >> different variants of it for different data formats?
> > >>
> > >> The points for this is again to keep the main API clean. The points
> > >> against this is that it duplicates the API, increases the surface area
> > >>and
> > >> creates redundancy for a minor addition.
> > >>
> > >> 3. Do we need to support different data types per record? The current
> > >> interface (bytes in/bytes out) lets you instantiate one producer and
> use
> > >> it to send multiple data formats. There seems to be some valid use
> cases
> > >> for this.
> > >>
> > >> I have still not seen a strong argument against not having this
> > >> functionality. Can someone provide their views on why we don't need
> this
> > >> support that is possible with the current API?
> > >>
> > >> One possible approach for the per record serialization would be to
> > >>define
> > >>
> > >> public interface SerDe<K,V> {
> > >> public byte[] serializeKey();
> > >>
> > >> public K deserializeKey();
> > >>
> > >> public byte[] serializeValue();
> > >>
> > >> public V deserializeValue();
> > >> }
> > >>
> > >> This would be used by both the Producer and the Consumer.
> > >>
> > >> The send APIs can then be
> > >>
> > >> public Future<RecordMetadata> send(ProducerRecord<K,V> record);
> > >> public Future<RecordMetadata> send(ProducerRecord<K,V> record,
> Callback
> > >> callback);
> > >>
> > >>
> > >> public Future<RecordMetadata> send(ProducerRecord<K,V> record,
> > >>SerDe<K,V>
> > >> serde);
> > >>
> > >> public Future<RecordMetadata> send(ProducerRecord<K,V> record,
> > >>SerDe<K,V>
> > >> serde, Callback callback);
> > >>
> > >>
> > >> A default SerDe can be set in the config. The producer would use the
> > >> default from the config if the non-serde send APIs are used. The
> > >>downside
> > >> to this approach is that we would need to have four variants of Send
> API
> > >> for the Producer.
> > >>
> > >>
> > >>
> > >>
> > >>
> > >>
> > >> On 12/5/14 3:16 PM, "Jun Rao" <j...@confluent.io> wrote:
> > >>
> > >> >Jiangjie,
> > >> >
> > >> >The issue with adding the serializer in ProducerRecord is that you
> > >>need to
> > >> >implement all combinations of serializers for key and value. So,
> > >>instead
> > >> >of
> > >> >just implementing int and string serializers, you will have to
> > >>implement
> > >> >all 4 combinations.
> > >> >
> > >> >Adding a new producer constructor like Producer<K,
> V>(KeySerializer<K>,
> > >> >ValueSerializer<V>, Properties properties) can be useful.
> > >> >
> > >> >Thanks,
> > >> >
> > >> >Jun
> > >> >
> > >> >On Thu, Dec 4, 2014 at 10:33 AM, Jiangjie Qin
> > >><j...@linkedin.com.invalid>
> > >> >wrote:
> > >> >
> > >> >>
> > >> >> 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" <jun...@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
> > >> >>
> > >> >>
> > >>
> > >>
> >
>
>
