Mikeal,
When you use `through(..)` topics are not created by KafkaStreams. You need
to create them yourself before you run the application.
Thanks,
Damian
On Thu, 24 Nov 2016 at 11:27 Mikael Högqvist <hoegqv...@gmail.com> wrote:
> Yes, the naming is not an issue.
>
> I've tested this with the topology described earlier. Every time I start
> the topology with a call to .through() that references a topic that does
> not exist, I get an exception from the UncaughtExceptionHandler:
>
> Uncaught exception org.apache.kafka.streams.errors.StreamsException: Topic
> not found during partition assignment: words-count-changelog
>
> This happens when .through("words-count-changelog", "count") is part of the
> topology. The topology is also not forwarding anything to that topic/store.
> After restarting the application it works fine.
>
> Are the changelog topics created via, for example, .aggregate() different
> to topics auto created via .through()?
>
> Thanks,
> Mikael
>
> On Wed, Nov 23, 2016 at 7:57 PM Matthias J. Sax <matth...@confluent.io>
> wrote:
>
> > > 1) Create a state store AND the changelog
> > > topic 2) follow the Kafka Streams naming convention for changelog
> topics.
> > > Basically, I want to have a method that does what .through() is
> supposed
> > to
> > > do according to the documentation, but without the "topic" parameter.
> >
> > I understand what you are saying, but you can get this done right now,
> > too. If you use through(...) you will get the store. And you can just
> > specify the topic name as "applicationId-storeName-changelog" to follow
> > the naming convention Streams used internally. What is the problem using
> > this approach (besides that you have to provide the topic name which
> > seems not to be a big burden to me?)
> >
> >
> > -Matthias
> >
> >
> > On 11/23/16 8:59 AM, Mikael Högqvist wrote:
> > > Hi Michael,
> > >
> > > thanks for the extensive explanation, and yes it definitely helps with
> my
> > > understanding of through(). :)
> > >
> > > You guessed correctly that I'm doing some "shenanings" where I'm trying
> > to
> > > derive the changelog of a state store from the state store name. This
> > works
> > > perfectly fine with with a naming convention for the topics and by
> > creating
> > > them in Kafka upfront.
> > >
> > > My point is that it would help me (and maybe others), if the API of
> > KTable
> > > was extended to have a new method that does two things that is not part
> > of
> > > the implementation of .through(). 1) Create a state store AND the
> > changelog
> > > topic 2) follow the Kafka Streams naming convention for changelog
> topics.
> > > Basically, I want to have a method that does what .through() is
> supposed
> > to
> > > do according to the documentation, but without the "topic" parameter.
> > >
> > > What do you think, would it be possible to extend the API with a method
> > > like that?
> > >
> > > Thanks,
> > > Mikael
> > >
> > > On Wed, Nov 23, 2016 at 4:16 PM Michael Noll <mich...@confluent.io>
> > wrote:
> > >
> > >> Mikael,
> > >>
> > >> regarding your second question:
> > >>
> > >>> 2) Regarding the use case, the topology looks like this:
> > >>>
> > >>> .stream(...)
> > >>> .aggregate(..., "store-1")
> > >>> .mapValues(...)
> > >>> .through(..., "store-2")
> > >>
> > >> The last operator above would, without "..." ellipsis, be sth like
> > >> `KTable#through("through-topic", "store-2")`. Here, "through-topic"
> is
> > the
> > >> changelog topic for both the KTable and the state store "store-2". So
> > this
> > >> is the changelog topic name that you want to know.
> > >>
> > >> - If you want the "through" topic to have a `-changelog` suffix, then
> > you'd
> > >> need to add that yourself in the call to `through(...)`.
> > >>
> > >> - If you wonder why `through()` doesn't add a `-changelog` suffix
> > >> automatically: That's because `through()` -- like `to()` or
> `stream()`,
> > >> `table()` -- require you to explicitly provide a topic name, and of
> > course
> > >> Kafka will use exactly this name. (FWIW, the `-changelog` suffix is
> > only
> > >> added when Kafka creates internal changelog topics behind the scenes
> for
> > >> you.) Unfortunately, the javadocs of `KTable#through()` is incorrect
> > >> because it refers to `-changelog`; we'll fix that as mentioned above.
> > >>
> > >> - Also, in case you want to do some shenanigans (like for some tooling
> > >> you're building around state stores/changelogs/interactive queries)
> such
> > >> detecting all state store changelogs by doing the equivalent of `ls
> > >> *-changelog`, then this will miss changelogs of KTables that are
> > created by
> > >> `through()` and `to()` (unless you come up with a naming convention
> that
> > >> your tooling can assume to be in place, e.g. by always adding
> > `-changelog`
> > >> to topic names when you call `through()`).
> > >>
> > >> I hope this helps!
> > >> Michael
> > >>
> > >>
> > >>
> > >>
> > >> On Wed, Nov 23, 2016 at 7:39 AM, Mikael Högqvist <hoegqv...@gmail.com
> >
> > >> wrote:
> > >>
> > >>> Hi Eno,
> > >>>
> > >>> 1) Great :)
> > >>>
> > >>> 2) Yes, we are using the Interactive Queries to access the state
> > stores.
> > >> In
> > >>> addition, we access the changelogs to subscribe to updates. For this
> > >> reason
> > >>> we need to know the changelog topic name.
> > >>>
> > >>> Thanks,
> > >>> Mikael
> > >>>
> > >>> On Tue, Nov 22, 2016 at 8:43 PM Eno Thereska <eno.there...@gmail.com
> >
> > >>> wrote:
> > >>>
> > >>>> HI Mikael,
> > >>>>
> > >>>> 1) The JavaDoc looks incorrect, thanks for reporting. Matthias is
> > >> looking
> > >>>> into fixing it. I agree that it can be confusing to have topic names
> > >> that
> > >>>> are not what one would expect.
> > >>>>
> > >>>> 2) If your goal is to query/read from the state stores, you can use
> > >>>> Interactive Queries to do that (you don't need to worry about the
> > >>> changelog
> > >>>> topic name and such). Interactive Queries is a new feature in 0.10.1
> > >>> (blog
> > >>>> here:
> > >>>> https://www.confluent.io/blog/unifying-stream-processing-
> > >>> and-interactive-queries-in-apache-kafka/
> > >>>> <
> > >>>> https://www.confluent.io/blog/unifying-stream-processing-
> > >>> and-interactive-queries-in-apache-kafka/
> > >>>>> ).
> > >>>>
> > >>>> Thanks
> > >>>> Eno
> > >>>>
> > >>>>
> > >>>>> On 22 Nov 2016, at 19:27, Mikael Högqvist <hoegqv...@gmail.com>
> > >> wrote:
> > >>>>>
> > >>>>> Sorry for being unclear, i'll try again :)
> > >>>>>
> > >>>>> 1) The JavaDoc for through is not correct, it states that a
> changelog
> > >>>> topic
> > >>>>> will be created for the state store. That is, if I would call it
> with
> > >>>>> through("topic", "a-store"), I would expect a kafka topic
> > >>>>> "my-app-id-a-store-changelog" to be created.
> > >>>>>
> > >>>>> 2) Regarding the use case, the topology looks like this:
> > >>>>>
> > >>>>> .stream(...)
> > >>>>> .aggregate(..., "store-1")
> > >>>>> .mapValues(...)
> > >>>>> .through(..., "store-2")
> > >>>>>
> > >>>>> Basically, I want to materialize both the result from the aggregate
> > >>>> method
> > >>>>> and the result from mapValues, which is materialized using
> > >> .through().
> > >>>>> Later, I will access both the tables (store-1 and store-2) to a)
> get
> > >>> the
> > >>>>> current state of the aggregate, b) subscribe to future updates.
> This
> > >>>> works
> > >>>>> just fine. The only issue is that I assumed to have a changelog
> topic
> > >>> for
> > >>>>> store-2 created automatically, which didnt happen.
> > >>>>>
> > >>>>> Since I want to access the changelog topic, it helps if the naming
> is
> > >>>>> consistent. So either we enforce the same naming pattern as kafka
> > >> when
> > >>>>> calling .through() or alternatively the Kafka Streams API can
> > >> provide a
> > >>>>> method to materialize tables which creates a topic name according
> to
> > >>> the
> > >>>>> naming pattern. E.g. .through() without the topic parameter.
> > >>>>>
> > >>>>> What do you think?
> > >>>>>
> > >>>>> Best,
> > >>>>> Mikael
> > >>>>>
> > >>>>> On Tue, Nov 22, 2016 at 7:21 PM Matthias J. Sax <
> > >> matth...@confluent.io
> > >>>>
> > >>>>> wrote:
> > >>>>>
> > >>>>>> I cannot completely follow what want to achieve.
> > >>>>>>
> > >>>>>> However, the JavaDoc for through() seems not to be correct to me.
> > >>> Using
> > >>>>>> through() will not create an extra internal changelog topic with
> the
> > >>>>>> described naming schema, because the topic specified in through()
> > >> can
> > >>> be
> > >>>>>> used for this (there is no point in duplicating the data).
> > >>>>>>
> > >>>>>> If you have a KTable and apply a mapValues(), this will not write
> > >> data
> > >>>>>> to any topic. The derived KTable is in-memory because you can
> easily
> > >>>>>> recreate it from its base KTable.
> > >>>>>>
> > >>>>>> What is the missing part you want to get?
> > >>>>>>
> > >>>>>> Btw: the internally created changelog topics are only used for
> > >>> recovery
> > >>>>>> in case of failure. Streams does not consumer from those topic
> > >> during
> > >>>>>> "normal operation".
> > >>>>>>
> > >>>>>>
> > >>>>>> -Matthias
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>> On 11/22/16 1:59 AM, Mikael Högqvist wrote:
> > >>>>>>> Hi,
> > >>>>>>>
> > >>>>>>> in the documentation for KTable#through, it is stated that a new
> > >>>>>> changelog
> > >>>>>>> topic will be created for the table. It also states that calling
> > >>>> through
> > >>>>>> is
> > >>>>>>> equivalent to calling #to followed by KStreamBuilder#table.
> > >>>>>>>
> > >>>>>>>
> > >>>>>>
> > >>>> http://kafka.apache.org/0101/javadoc/org/apache/kafka/
> > >>> streams/kstream/KTable.html#through(org.apache.kafka.
> > >>> common.serialization.Serde,%20org.apache.kafka.common.
> > >>> serialization.Serde,%20java.lang.String,%20java.lang.String)
> > >>>>>>>
> > >>>>>>> In the docs for KStreamBuilder#table it is stated that no new
> > >>> changelog
> > >>>>>>> topic will be created since the underlying topic acts as the
> > >>> changelog.
> > >>>>>>> I've verified that this is the case.
> > >>>>>>>
> > >>>>>>> Is there another API method to materialize the results of a
> KTable
> > >>>>>>> including a changelog, i.e. such that kafka streams creates the
> > >> topic
> > >>>> and
> > >>>>>>> uses the naming schema for changelog topics? The use case I have
> in
> > >>>> mind
> > >>>>>> is
> > >>>>>>> aggregate followed by mapValues.
> > >>>>>>>
> > >>>>>>> Best,
> > >>>>>>> Mikael
> > >>>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>
> > >>>>
> > >>>
> > >>
> > >
> >
> >
>
