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From Development <...@yeralin.net>
Subject Re: [DISCUSS] KIP-466: Add support for List<T> serialization and deserialization
Date Wed, 10 Jul 2019 15:52:09 GMT
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> 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>>
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>>
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>>
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:+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>>
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>>> 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>
> >
> > 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>>> 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>>> 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>>> 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>>>> 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>>
> >  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>>>> 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>>>> 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>>
> >  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>>>> wrote:
> >
> >
> >  bump
> >
> >
> >
> >
> >
> >
> >
> >


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