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From Development <...@yeralin.net>
Subject Re: [DISCUSS] KIP-466: Add support for List<T> serialization and deserialization
Date Tue, 16 Jul 2019 19:05:14 GMT
Hi,

Pushed new changes under my PR: https://github.com/apache/kafka/pull/6592 <https://github.com/apache/kafka/pull/6592>

Feel free to put any comments in there.

Best,
Daniyar Yeralin

> On Jul 15, 2019, at 1:06 PM, Development <dev@yeralin.net> wrote:
> 
> Hi John,
> 
> I knew I was missing something. Yes, that makes sense now, I removed all `listSerde()`
methods, and left empty constructors instead.
> 
> As per `CommonClientConfigs` I looked at the class, it doesn’t have any properties
related to serdes, and that bothers me a little.
> 
> All properties like `default.key.serde` `default.windowed.key.serde.*` are located in
StreamsConfig. I don’t want to create a confusion.
> What also doesn’t make sense to me is that `WindowedSerdes` and its (de)serializers
are not located in org.apache.kafka.common.serialization. I guess it kind of makes sense since
windowed serdes are only available for kafka streams, not vice versa. 
> 
> If everyone is okay to put list properties in `CommonClientConfigs` class, I’ll go
ahead and do that then.
> 
> Thank you for your input!
> 
> Best,
> Daniyar Yeralin
> 
>> On Jul 15, 2019, at 11:45 AM, John Roesler <john@confluent.io> wrote:
>> 
>> Hi all,
>> 
>> Regarding the placement, you might as well move the constants to `org.apache.kafka.clients.CommonClientConfigs`,
so that the constants and the configs and the code are in the same module.
>> 
>> Regarding the constructor... What Matthias said is correct: The serde, serializer,
and deserializer all need to have zero-arg constructors so they can be instantiated reflectively
by Kafka. However, the factory method you proposed "New method public static <T> Serde<List<T>>
ListSerde()" is not a constructor, and is not required. It would be used purely from the Java
interface, but has the drawbacks I listed above. This method, not the constructor, is what
I proposed to remove from the KIP.
>> 
>> Thanks,
>> -John
>> 
>> 
>> On Mon, Jul 15, 2019 at 10:15 AM Development <dev@yeralin.net <mailto:dev@yeralin.net>>
wrote:
>> One problem though. 
>> 
>> Since WindowedSerde (Windowed(De)Serializer) are so similar, I’m trying to mimic
the implementation of my ListSerde accordingly.
>> 
>> I created couple constants under StreamsConfig:
>> 
>> 
>> 
>> And trying to do similar construct:
>> final String propertyName = isKey ? StreamsConfig.DEFAULT_LIST_KEY_SERDE_INNER_CLASS
: StreamsConfig.DEFAULT_LIST_VALUE_SERDE_INNER_CLASS;
>> But then found out that StreamsConfig is not accessible from org.apache.kafka.common.serialization
package while window serde (de)serializers are located under org.apache.kafka.streams.kstream
package.
>> 
>> What should I do? Should I move my classes under org.apache.kafka.streams.kstream
package instead?
>> 
>>> On Jul 15, 2019, at 10:45 AM, Development <dev@yeralin.net <mailto:dev@yeralin.net>>
wrote:
>>> 
>>> Hi Matthias,
>>> 
>>> Thank you for your input.
>>> 
>>> I updated the KIP, made it a little more readable.
>>> 
>>> I think the configuration parameters strategy is finalized then.
>>> 
>>> Do you have any other questions/concerns regarding this KIP?
>>> 
>>> Meanwhile I’ll start doing appropriate code changes, and commit them under
my PR.
>>> 
>>> Best,
>>> Daniyar Yeralin
>>> 
>>>> On Jul 11, 2019, at 2:44 PM, Matthias J. Sax <matthias@confluent.io <mailto:matthias@confluent.io>>
wrote:
>>>> 
>>>> Daniyar,
>>>> 
>>>> thanks for the update to the KIP. It's in really good shape and well
>>>> written.
>>>> 
>>>> About the default constructor question:
>>>> 
>>>> All Serdes/Serializer/Deserializer classes need a default constructor to
>>>> create them easily via reflections when specifies in a config. I
>>>> understand that it is not super user friendly, but all existing code
>>>> works this way. Hence, it seems best to stick with the established pattern.
>>>> 
>>>> We have a similar issue with `TimeWindowedSerde` and
>>>> `SessionWindowedSerde`, and I just recently did a PR to improve user
>>>> experience that address the exact issue John raised. (cf
>>>> https://github.com/apache/kafka/pull/7067 <https://github.com/apache/kafka/pull/7067>)
>>>> 
>>>> Note, that if a user would instantiate the Serde manually, the user
>>>> would also need to call `configure()` to setup the inner serdes. Kafka
>>>> Streams would not setup those automatically and one might most likely
>>>> end-up with an NPE.
>>>> 
>>>> 
>>>> Coming back the KIP, and the parameter names. `WindowedSerdes` are
>>>> similar to `ListSerde` as they wrap another Serde. For `WindowedSerdes`,
>>>> we use the following parameter names:
>>>> 
>>>> - default.windowed.key.serde.inner
>>>> - default.windowed.value.serde.inner
>>>> 
>>>> 
>>>> It might be good to align the naming pattern. I would also suggest to
>>>> use `type` instead of `impl`?
>>>> 
>>>> 
>>>> default.key.list.serde.impl  ->  default.list.key.serde.type
>>>> default.value.list.serde.impl  ->  default.list.value.serde.type
>>>> default.key.list.serde.element  ->  default.list.key.serde.inner
>>>> default.value.list.serde.element  ->  default.list.value.serde.inner
>>>> 
>>>> 
>>>> 
>>>> -Matthias
>>>> 
>>>> 
>>>> On 7/10/19 8:52 AM, Development wrote:
>>>>> Hi John,
>>>>> 
>>>>> Yes, I do agree. That totally makes sense. The only thing is that it
goes against what Matthias suggested earlier:
>>>>> "I think that ... `ListSerde` should have an default constructor and
it should be possible to pass in the `Class listClass` information via a configuration. Otherwise,
KafkaStreams cannot use it as default serde.”
>>>>> 
>>>>> What do you think about that? I hope I’m not confusing anything.
>>>>> 
>>>>> Best,
>>>>> Daniyar Yeralin
>>>>> 
>>>>>> On Jul 9, 2019, at 5:56 PM, John Roesler <john@confluent.io <mailto:john@confluent.io>>
wrote:
>>>>>> 
>>>>>> Ah, my apologies, I must have just overlooked it. Thanks for the
update, too.
>>>>>> 
>>>>>> Just one more super-small question, do we need this variant: 
>>>>>> 
>>>>>>> New method public static <T> Serde<List<T>>
ListSerde() in org.apache.kafka.common.serialization.Serdes class (infers list implementation
and inner serde from config file)
>>>>>> 
>>>>>> It seems like this situation implies my config file is already set
up for the list serde, so passing this serde (e.g., in Produced) would have the same effect
as not specifying it. 
>>>>>> 
>>>>>> I guess that it could be the case that you have the `default.key/value.serde`
set to something else, like StringSerde, but you still have the `default.key/value.list.serde.impl/element`
set. This seems like it would result in more confusion than convenience, so my gut instinct
is maybe we shouldn't introduce the `ListSerde()` variant until people actually request it
later on.
>>>>>> 
>>>>>> Thus, we'd just stick with fully config-driven or fully source-code-driven,
not half/half.
>>>>>> 
>>>>>> What do you think?
>>>>>> 
>>>>>> Thanks,
>>>>>> -John
>>>>>> 
>>>>>> 
>>>>>> On Tue, Jul 9, 2019 at 9:58 AM Development <dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>> wrote:
>>>>>>> 
>>>>>>> Hi John,
>>>>>>> 
>>>>>>> I hope everyone had a great long weekend.
>>>>>>> 
>>>>>>> Regarding Java interfaces, I may not understand you correctly,
but I think I already listed them:
>>>>>>> 
>>>>>>> So for Produced, you would use it in the following fashion, for
example: Produced.keySerde(Serdes.ListSerde(ArrayList.class, Serdes.Integer()))
>>>>>>> 
>>>>>>> I also updated the KIP, and added a section “Serialization
Strategy” where I describe our logic of conditional serialization based on the type of an
inner serde.
>>>>>>> 
>>>>>>> Thank you!
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> On Jun 26, 2019, at 11:44 AM, John Roesler <john@confluent.io
<mailto:john@confluent.io> <mailto:john@confluent.io <mailto:john@confluent.io>>>
wrote:
>>>>>>> 
>>>>>>> Thanks for the update, Daniyar!
>>>>>>> 
>>>>>>> In addition to specifying the config interface, can you also
specify
>>>>>>> the Java interface? Namely, if I need to pass an instance of
this
>>>>>>> serde in to the DSL directly, as in Produced, Materialized, etc.,
what
>>>>>>> constructor(s) would I have available? Likewise with the Serializer
>>>>>>> and Deserailizer. I don't think you need to specify the implementation
>>>>>>> logic, since we've already discussed it here.
>>>>>>> 
>>>>>>> If you also want to specify the serialized format of the data
records
>>>>>>> in the KIP, it could be useful documentation, as well as letting
us
>>>>>>> verify the schema for forward/backward compatibility concerns,
etc.
>>>>>>> 
>>>>>>> Thanks,
>>>>>>> John
>>>>>>> 
>>>>>>> On Wed, Jun 26, 2019 at 10:33 AM Development <dev@yeralin.net
<mailto:dev@yeralin.net> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>
wrote:
>>>>>>> 
>>>>>>> 
>>>>>>> Hey,
>>>>>>> 
>>>>>>> Finally made updates to the KIP: https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization>
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466%3A+Add+support+for+List%3CT%3E+serialization+and+deserialization>>
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization>
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-466:+Add+support+for+List%3CT%3E+serialization+and+deserialization>>>
>>>>>>> Sorry for the delay :)
>>>>>>> 
>>>>>>> Thank You!
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> On Jun 22, 2019, at 12:49 AM, Matthias J. Sax <matthias@confluent.io
<mailto:matthias@confluent.io> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>>>
wrote:
>>>>>>> 
>>>>>>> Yes, something like this. I did not think about good configuration
>>>>>>> parameter names yet. I am also not sure if I understand all proposed
>>>>>>> configs atm. But all configs should be listed and explained in
the KIP
>>>>>>> anyway, and we can discuss further after you have updated the
KIP (I can
>>>>>>> ask more detailed question if I have any).
>>>>>>> 
>>>>>>> 
>>>>>>> -Matthias
>>>>>>> 
>>>>>>> On 6/21/19 2:05 PM, Development wrote:
>>>>>>> 
>>>>>>> Yes, you are right. ByteSerializer is not what I need to have
in a list
>>>>>>> of primitives.
>>>>>>> 
>>>>>>> As for the default constructor and configurability, just want
to make
>>>>>>> sure. Is this what you have on your mind?
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On Jun 21, 2019, at 2:51 PM, Matthias J. Sax <matthias@confluent.io
<mailto:matthias@confluent.io> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>>
>>>>>>> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>
<mailto:matthias@confluent.io <mailto:matthias@confluent.io>>>> wrote:
>>>>>>> 
>>>>>>> Thanks for the update!
>>>>>>> 
>>>>>>> I think that `ListDeserializer`, `ListSerializer`, and `ListSerde`
>>>>>>> should have an default constructor and it should be possible
to pass in
>>>>>>> the `Class listClass` information via a configuration. Otherwise,
>>>>>>> KafkaStreams cannot use it as default serde.
>>>>>>> 
>>>>>>> 
>>>>>>> For the primitive serializers: `BytesSerializer` is not primitive
IMHO,
>>>>>>> as is it for `byte[]` with variable length -- it's for arrays,
not for
>>>>>>> single `byte` (note, that `Bytes` is a Kafka class wrapping `byte[]`).
>>>>>>> 
>>>>>>> 
>>>>>>> For tests, we can comment on the PR. No need to do this in the
KIP
>>>>>>> discussion.
>>>>>>> 
>>>>>>> 
>>>>>>> Can you also update the KIP?
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> -Matthias
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On 6/21/19 11:29 AM, Development wrote:
>>>>>>> 
>>>>>>> I made and pushed necessary commits, so we could review the final
>>>>>>> version under PR https://github.com/apache/kafka/pull/6592 <https://github.com/apache/kafka/pull/6592>
<https://github.com/apache/kafka/pull/6592 <https://github.com/apache/kafka/pull/6592>>
>>>>>>> 
>>>>>>> I also need some advice on writing tests for this new serde.
So far I
>>>>>>> only have two test cases (roundtrip and empty payload), I’m
not sure
>>>>>>> if it is enough.
>>>>>>> 
>>>>>>> Thank y’all for your help in this KIP :)
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> 
>>>>>>> On Jun 21, 2019, at 1:44 PM, John Roesler <john@confluent.io
<mailto:john@confluent.io> <mailto:john@confluent.io <mailto:john@confluent.io>>
>>>>>>> <mailto:john@confluent.io <mailto:john@confluent.io>
<mailto:john@confluent.io <mailto:john@confluent.io>>>> wrote:
>>>>>>> 
>>>>>>> Hey Daniyar,
>>>>>>> 
>>>>>>> Looks good to me! Thanks for considering it.
>>>>>>> 
>>>>>>> Thanks,
>>>>>>> -John
>>>>>>> 
>>>>>>> On Fri, Jun 21, 2019 at 9:04 AM Development <dev@yeralin.net
<mailto:dev@yeralin.net> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>> wrote:
>>>>>>> Hey John and Matthias,
>>>>>>> 
>>>>>>> Yes, now I see it all. I’m storing lots of redundant information.
>>>>>>> Here is my final idea. Yes, now a user should pass a list type.
I
>>>>>>> realized that’s the type is not really needed in ListSerializer,
but
>>>>>>> only in ListDeserializer:
>>>>>>> 
>>>>>>> 
>>>>>>> In ListSerializer we will start storing sizes only if serializer
is
>>>>>>> not a primitive serializer:
>>>>>>> 
>>>>>>> 
>>>>>>> Then, in deserializer, we persist passed list type, so that during
>>>>>>> deserialization we could create an instance of it with predefined
>>>>>>> listSize for better performance.
>>>>>>> We also try to locate a primitiveSize based on passed deserializer.
>>>>>>> If it is not there, then primitiveSize will be null. Which means
>>>>>>> that each entry’s size was encoded individually.
>>>>>>> 
>>>>>>> 
>>>>>>> This looks much cleaner and more concise.
>>>>>>> 
>>>>>>> What do you think?
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> On Jun 20, 2019, at 5:45 PM, Matthias J. Sax <matthias@confluent.io
<mailto:matthias@confluent.io> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>>
>>>>>>> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>
<mailto:matthias@confluent.io <mailto:matthias@confluent.io>>> <mailto:matthias@confluent.io
<mailto:matthias@confluent.io> <mailto:matthias@confluent.io <mailto:matthias@confluent.io>>>>
wrote:
>>>>>>> 
>>>>>>> For encoding the list-type: I see John's point about re-encoding
the
>>>>>>> list-type redundantly. However, I also don't like the idea that
the
>>>>>>> Deserializer returns a fixed type...
>>>>>>> 
>>>>>>> Maybe it's best allow users to specify the target list type on
>>>>>>> deserialization via config?
>>>>>>> 
>>>>>>> Similar for the primitive types: I don't think we need to encode
the
>>>>>>> type size, but users could specify the type on the deserializer
(via a
>>>>>>> config again)?
>>>>>>> 
>>>>>>> 
>>>>>>> About generics: nesting could be arbitrarily deep. Hence, I doubt
>>>>>>> we can
>>>>>>> support this and a cast will be necessary at some point in the
user
>>>>>>> code.
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> -Matthias
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> On 6/20/19 1:21 PM, John Roesler wrote:
>>>>>>> 
>>>>>>> Hey Daniyar,
>>>>>>> 
>>>>>>> Thanks for looking at it!
>>>>>>> 
>>>>>>> Something like your screenshot is more along the lines of what
I was
>>>>>>> thinking. Sorry, but I didn't follow what you mean, how would
that not
>>>>>>> be "vanilla java"?
>>>>>>> 
>>>>>>> Unfortunately the deserializer needs more information, though.
For
>>>>>>> example, what if the inner type is a Map<String,String>?
The serde
>>>>>>> could
>>>>>>> only be used to produce a LinkedList<Map>, thus, we'd still
need an
>>>>>>> inner serde, like you have in the KIP (Serde<T> innerSerde).
>>>>>>> 
>>>>>>> Something more like Serde<LinkedList<MyRecord>> =
Serdes.listSerde(
>>>>>>> /**list type**/ LinkedList.class,
>>>>>>> /**inner serde**/ new MyRecordSerde()
>>>>>>> )
>>>>>>> 
>>>>>>> And in configuration, it's something like:
>>>>>>> default.key.serde: org...ListSerde
>>>>>>> default.key.list.serde.type: java.util.LinkedList
>>>>>>> default.key.list.serde.inner: com.mycompany.MyRecordSerde
>>>>>>> 
>>>>>>> 
>>>>>>> What do you think?
>>>>>>> Thanks,
>>>>>>> -John
>>>>>>> 
>>>>>>> On Thu, Jun 20, 2019 at 2:46 PM Development <dev@yeralin.net
<mailto:dev@yeralin.net> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>>> wrote:
>>>>>>> 
>>>>>>> Hey John,
>>>>>>> 
>>>>>>> I gave read about TypeReference. It could work for the list serde.
>>>>>>> However, it is not directly
>>>>>>> supported:
>>>>>>> https://github.com/FasterXML/jackson-databind/issues/1490 <https://github.com/FasterXML/jackson-databind/issues/1490>
<https://github.com/FasterXML/jackson-databind/issues/1490 <https://github.com/FasterXML/jackson-databind/issues/1490>>
>>>>>>> <https://github.com/FasterXML/jackson-databind/issues/1490
<https://github.com/FasterXML/jackson-databind/issues/1490> <https://github.com/FasterXML/jackson-databind/issues/1490
<https://github.com/FasterXML/jackson-databind/issues/1490>>>
>>>>>>> The only way is to pass an actual class object into the constructor,
>>>>>>> something like:
>>>>>>> 
>>>>>>> It could be an option, but not a pretty one. What do you think
of my
>>>>>>> approach to use vanilla java and canonical class name? (As described
>>>>>>> previously)
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> On Jun 20, 2019, at 2:45 PM, Development <dev@yeralin.net
<mailto:dev@yeralin.net> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>>> wrote:
>>>>>>> 
>>>>>>> Hi John,
>>>>>>> 
>>>>>>> Thank you for your input! Yes, my idea looks a little bit over
>>>>>>> engineered :)
>>>>>>> 
>>>>>>> I also wanted to see a feedback from Mathias as well since he
gave
>>>>>>> me an idea about storing fixed/variable size entries.
>>>>>>> 
>>>>>>> Best,
>>>>>>> Daniyar Yeralin
>>>>>>> 
>>>>>>> On Jun 18, 2019, at 6:06 PM, John Roesler <john@confluent.io
<mailto:john@confluent.io> <mailto:john@confluent.io <mailto:john@confluent.io>>
>>>>>>> <mailto:john@confluent.io <mailto:john@confluent.io>
<mailto:john@confluent.io <mailto:john@confluent.io>>> <mailto:john@confluent.io
<mailto:john@confluent.io> <mailto:john@confluent.io <mailto:john@confluent.io>>>
>>>>>>> <mailto:john@confluent.io <mailto:john@confluent.io>
<mailto:john@confluent.io <mailto:john@confluent.io>> <mailto:john@confluent.io
<mailto:john@confluent.io> <mailto:john@confluent.io <mailto:john@confluent.io>>>>>
wrote:
>>>>>>> 
>>>>>>> Hi Daniyar,
>>>>>>> 
>>>>>>> That's a very clever solution!
>>>>>>> 
>>>>>>> One observation is that, now, this is what we might call a
>>>>>>> polymorphic
>>>>>>> serde. That is, you're detecting the actual concrete type and
then
>>>>>>> promising to produce the exact same concrete type on read.
>>>>>>> There are
>>>>>>> some inherent problems with this approach, which in general
>>>>>>> require
>>>>>>> some kind of  schema registry (not necessarily Schema
>>>>>>> Registry, just
>>>>>>> any registry for schemas) to solve.
>>>>>>> 
>>>>>>> Notice that every serialized record has quite a bit of duplicated
>>>>>>> information: the concrete type as well as a byte to indicate
>>>>>>> whether
>>>>>>> the value type is a fixed size, and, if so, an integer to
>>>>>>> indicate the
>>>>>>> actual size. These constitute a schema, of sorts, because they
>>>>>>> tell us
>>>>>>> later how exactly to deserialize the data. Unfortunately, this
>>>>>>> information is completely redundant. In all likelihood, the
>>>>>>> information will be exactly the same for every record in the
>>>>>>> topic.
>>>>>>> This problem is essentially the core motivation for serializations
>>>>>>> like Avro: to move the schema outside of the serialization
>>>>>>> itself, so
>>>>>>> that the records won't contain so much redundant information.
>>>>>>> 
>>>>>>> In this light, I'm wondering if it makes sense to go back to
>>>>>>> something
>>>>>>> like what you had earlier in which you don't support perfectly
>>>>>>> preserving the concrete type for _this_ serde, but instead just
>>>>>>> support deserializing to _some_ List. Then, you could defer full,
>>>>>>> perfect, type preservation to serdes that have an external
>>>>>>> system in
>>>>>>> which to register their type information.
>>>>>>> 
>>>>>>> There does exist an alternative, if we really do want to
>>>>>>> preserve the
>>>>>>> concrete type (which does seem kind of nice). You can add a
>>>>>>> configuration option specifically for the serde to configure
>>>>>>> what the
>>>>>>> list type will be, and maybe what the element type is, as well.
>>>>>>> 
>>>>>>> As far as "related work" goes, you might be interested to take
>>>>>>> a look
>>>>>>> at how Jackson can be configured to deserialize into a specific,
>>>>>>> arbitrarily nested, generically parameterized class structure.
>>>>>>> Specifically, you might find
>>>>>>> https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>>
>>>>>>> <https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html
<https://fasterxml.github.io/jackson-core/javadoc/2.0.0/com/fasterxml/jackson/core/type/TypeReference.html>>>
>>>>>>> interesting.
>>>>>>> 
>>>>>>> Thanks,
>>>>>>> -John
>>>>>>> 
>>>>>>> On Mon, Jun 17, 2019 at 12:38 PM Development <dev@yeralin.net
<mailto:dev@yeralin.net> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>
>>>>>>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net> <mailto:dev@yeralin.net
<mailto:dev@yeralin.net>> <mailto:dev@yeralin.net <mailto:dev@yeralin.net>
<mailto:dev@yeralin.net <mailto:dev@yeralin.net>>>>> wrote:
>>>>>>> 
>>>>>>> 
>>>>>>> bump
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>> 
>>>>> 
>>>> 
>>> 
>> 
> 


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