Hi Guozhang, Thanks for the feedback
On Thu, 29 Jun 2017 at 01:45 Guozhang Wang <wangg...@gmail.com> wrote: > I played the current proposal a bit with https://github.com/dguy/kafka/ > tree/dsl-experiment <https://github.com/dguy/kafka/tree/dsl-experiment>, > and here are my observations: > > 1. Personally I prefer > > "stream.group(mapper) / stream.groupByKey()" > > than > > "stream.group().withKeyMapper(mapper) / stream.group()" > > Since 1) withKeyMapper is not enforced programmatically though it is not > "really" optional like others, 2) syntax-wise it reads more natural. > > Yes, that is true. The keyMapper is not optional to `group` so should be an argument to the method > I think it is okay to add the APIs in ( > > https://github.com/dguy/kafka/blob/dsl-experiment/streams/src/main/java/org/apache/kafka/streams/kstream/GroupedStream.java > ) > in KGroupedStream. > > Are you saying add these methods to KGroupedStream? I'm not so sure as they'd all need to return a KGroupedStream and then we would need to be able to remove/replace/update processors in the topology (which would be achievable, but i think not before KIP-120 is done so that we don't expose any further public APIs that are only to support internal usages - also updating processors in the topology seems a bit odd IMO). Perhaps you mean something different. > > 2. For the "withStateStoreSupplier" API, are the user supposed to pass in > the most-inner state store supplier (e.g. then one whose get() return > RocksDBStore), or it is supposed to return the most-outer supplier with > logging / metrics / etc? I think it would be more useful to only require > users pass in the inner state store supplier while specifying caching / > logging through other APIs. > Yes that is possible, though in that case we might want to use a narrower interface than StateStoreSupplier, i.e., one that doesn't have `logConfig` and `loggingEnabled`? Those two methods are exposed for the `TopologyBuilder` > > In addition, the "GroupedWithCustomStore" is a bit suspicious to me: we are > allowing users to call other APIs like "withQueryableName" multiple time, > but only call "withStateStoreSupplier" only once in the end. Why is that? > > The API is not meant to be complete! It is just an experiment to see what is possible. However, at some point we need to decide which methods are valid at any point. So if you have called `withStateStoreSupplier` you no longer need to call `withQueryableName`, `withKeySerde`, `withValueSerde` etc as this is already done. The point being to narrow the interface to what makes sense. There is work to be done here! > > 3. The current DSL seems to be only for aggregations, what about joins? > > You have to start somewhere! I'd like to think we can come to an agreement on a style and then apply that across the board. So the API should look the same everywhere. But yes i can add some join examples. > > 4. I think it is okay to keep the "withLogConfig": for the > StateStoreSupplier it will still be user code specifying the topology so I > do not see there is a big difference. > > I guess this one of the most contentious points, i.e., mixing config with topology building. I'm on the fence on this as I get both sides of the argument. I also don't really like having everything in config. > > 5. "WindowedGroupedStream" 's withStateStoreSupplier should take the > windowed state store supplier to enforce typing? > > Yes it would. I was just doing a bare bones API so at least you could try it out. > > Below are minor ones: > > 6. "withQueryableName": maybe better "withQueryableStateName"? > I think we currently call it `queryableStoreName`. So maybe we stick with that? > > 7. "withLogConfig": maybe better "withLoggingTopicConfig()"? > > Yep > > Guozhang > > > > On Wed, Jun 28, 2017 at 3:59 PM, Matthias J. Sax <matth...@confluent.io> > wrote: > > > I see your point about "when to add the processor to the topology". That > > is indeed an issue. Not sure it we could allow "updates" to the > topology... > > > > I don't see any problem with having all the withXX() in KTable interface > > -- but this might be subjective. > > > > > > However, I don't understand your argument about putting aggregate() > > after the withXX() -- all the calls to withXX() set optional parameters > > for aggregate() and not for groupBy() -- but a groupBy().withXX() > > indicates that the withXX() belongs to the groupBy(). IMHO, this might > > be quite confusion for developers. > > > > > > -Matthias > > > > On 6/28/17 2:55 AM, Damian Guy wrote: > > >> I also think that mixing optional parameters with configs is a bad > idea. > > >> Have not proposal for this atm but just wanted to mention it. Hope to > > >> find some time to come up with something. > > >> > > >> > > > Yes, i don't like the mix of config either. But the only real config > here > > > is the logging config - which we don't really need as it can already be > > > done via a custom StateStoreSupplier. > > > > > > > > >> What I don't like in the current proposal is the > > >> .grouped().withKeyMapper() -- the current solution with .groupBy(...) > > >> and .groupByKey() seems better. For clarity, we could rename to > > >> .groupByNewKey(...) and .groupByCurrentKey() (even if we should find > > >> some better names). > > >> > > >> > > > it could be groupByKey(), groupBy() or something different bt > > > > > > > > > > > >> The proposed pattern "chains" grouping and aggregation too close > > >> together. I would rather separate both more than less, ie, do into the > > >> opposite direction. > > >> > > >> I am also wondering, if we could so something more "fluent". The > initial > > >> proposal was like: > > >> > > >>>> groupedStream.count() > > >>>> .withStoreName("name") > > >>>> .withCachingEnabled(false) > > >>>> .withLoggingEnabled(config) > > >>>> .table() > > >> > > >> The .table() statement in the end was kinda alien. > > >> > > > > > > I agree, but then all of the withXXX methods need to be on KTable which > > is > > > worse in my opinion. You also need something that is going to "build" > the > > > internal processors and add them to the topology. > > > > > > > > >> The current proposal put the count() into the end -- ie, the optional > > >> parameter for count() have to specified on the .grouped() call -- this > > >> does not seems to be the best way either. > > >> > > >> > > > I actually prefer this method as you are building a grouped stream that > > you > > > will aggregate. So table.grouped(...).withOptionalStuff().aggregate(..) > > etc > > > seems natural to me. > > > > > > > > >> I did not think this through in detail, but can't we just do the > initial > > >> proposal with the .table() ? > > >> > > >> groupedStream.count().withStoreName("name").mapValues(...) > > >> > > >> Each .withXXX(...) return the current KTable and all the .withXXX() > are > > >> just added to the KTable interface. Or do I miss anything why this > wont' > > >> work or any obvious disadvantage? > > >> > > >> > > >> > > > See above. > > > > > > > > >> > > >> -Matthias > > >> > > >> On 6/22/17 4:06 AM, Damian Guy wrote: > > >>> Thanks everyone. My latest attempt is below. It builds on the fluent > > >>> approach, but i think it is slightly nicer. > > >>> I agree with some of what Eno said about mixing configy stuff in the > > DSL, > > >>> but i think that enabling caching and enabling logging are things > that > > >>> aren't actually config. I'd probably not add withLogConfig(...) (even > > >>> though it is below) as this is actually config and we already have a > > way > > >> of > > >>> doing that, via the StateStoreSupplier. Arguably we could use the > > >>> StateStoreSupplier for disabling caching etc, but as it stands that > is > > a > > >>> bit of a tedious process for someone that just wants to use the > default > > >>> storage engine, but not have caching enabled. > > >>> > > >>> There is also an orthogonal concern that Guozhang alluded to.... If > you > > >>> want to plug in a custom storage engine and you want it to be logged > > etc, > > >>> you would currently need to implement that yourself. Ideally we can > > >> provide > > >>> a way where we will wrap the custom store with logging, metrics, > etc. I > > >>> need to think about where this fits, it is probably more appropriate > on > > >> the > > >>> Stores API. > > >>> > > >>> final KeyValueMapper<String, String, Long> keyMapper = null; > > >>> // count with mapped key > > >>> final KTable<Long, Long> count = stream.grouped() > > >>> .withKeyMapper(keyMapper) > > >>> .withKeySerde(Serdes.Long()) > > >>> .withValueSerde(Serdes.String()) > > >>> .withQueryableName("my-store") > > >>> .count(); > > >>> > > >>> // windowed count > > >>> final KTable<Windowed<String>, Long> windowedCount = stream.grouped() > > >>> .withQueryableName("my-window-store") > > >>> .windowed(TimeWindows.of(10L).until(10)) > > >>> .count(); > > >>> > > >>> // windowed reduce > > >>> final Reducer<String> windowedReducer = null; > > >>> final KTable<Windowed<String>, String> windowedReduce = > > stream.grouped() > > >>> .withQueryableName("my-window-store") > > >>> .windowed(TimeWindows.of(10L).until(10)) > > >>> .reduce(windowedReducer); > > >>> > > >>> final Aggregator<String, String, Long> aggregator = null; > > >>> final Initializer<Long> init = null; > > >>> > > >>> // aggregate > > >>> final KTable<String, Long> aggregate = stream.grouped() > > >>> .withQueryableName("my-aggregate-store") > > >>> .aggregate(aggregator, init, Serdes.Long()); > > >>> > > >>> final StateStoreSupplier<KeyValueStore<String, Long>> > > stateStoreSupplier > > >> = null; > > >>> > > >>> // aggregate with custom store > > >>> final KTable<String, Long> aggWithCustomStore = stream.grouped() > > >>> .withStateStoreSupplier(stateStoreSupplier) > > >>> .aggregate(aggregator, init); > > >>> > > >>> // disable caching > > >>> stream.grouped() > > >>> .withQueryableName("name") > > >>> .withCachingEnabled(false) > > >>> .count(); > > >>> > > >>> // disable logging > > >>> stream.grouped() > > >>> .withQueryableName("q") > > >>> .withLoggingEnabled(false) > > >>> .count(); > > >>> > > >>> // override log config > > >>> final Reducer<String> reducer = null; > > >>> stream.grouped() > > >>> .withLogConfig(Collections.singletonMap("segment.size", > "10")) > > >>> .reduce(reducer); > > >>> > > >>> > > >>> If anyone wants to play around with this you can find the code here: > > >>> https://github.com/dguy/kafka/tree/dsl-experiment > > >>> > > >>> Note: It won't actually work as most of the methods just return null. > > >>> > > >>> Thanks, > > >>> Damian > > >>> > > >>> > > >>> On Thu, 22 Jun 2017 at 11:18 Ismael Juma <ism...@juma.me.uk> wrote: > > >>> > > >>>> Thanks Damian. I think both options have pros and cons. And both are > > >> better > > >>>> than overload abuse. > > >>>> > > >>>> The fluent API approach reads better, no mention of builder or build > > >>>> anywhere. The main downside is that the method signatures are a > little > > >> less > > >>>> clear. By reading the method signature, one doesn't necessarily > knows > > >> what > > >>>> it returns. Also, one needs to figure out the special method > > (`table()` > > >> in > > >>>> this case) that gives you what you actually care about (`KTable` in > > this > > >>>> case). Not major issues, but worth mentioning while doing the > > >> comparison. > > >>>> > > >>>> The builder approach avoids the issues mentioned above, but it > doesn't > > >> read > > >>>> as well. > > >>>> > > >>>> Ismael > > >>>> > > >>>> On Wed, Jun 21, 2017 at 3:37 PM, Damian Guy <damian....@gmail.com> > > >> wrote: > > >>>> > > >>>>> Hi, > > >>>>> > > >>>>> I'd like to get a discussion going around some of the API choices > > we've > > >>>>> made in the DLS. In particular those that relate to stateful > > operations > > >>>>> (though this could expand). > > >>>>> As it stands we lean heavily on overloaded methods in the API, i.e, > > >> there > > >>>>> are 9 overloads for KGroupedStream.count(..)! It is becoming noisy > > and > > >> i > > >>>>> feel it is only going to get worse as we add more optional params. > In > > >>>>> particular we've had some requests to be able to turn caching off, > or > > >>>>> change log configs, on a per operator basis (note this can be done > > now > > >>>> if > > >>>>> you pass in a StateStoreSupplier, but this can be a bit > cumbersome). > > >>>>> > > >>>>> So this is a bit of an open question. How can we change the DSL > > >> overloads > > >>>>> so that it flows, is simple to use and understand, and is easily > > >> extended > > >>>>> in the future? > > >>>>> > > >>>>> One option would be to use a fluent API approach for providing the > > >>>> optional > > >>>>> params, so something like this: > > >>>>> > > >>>>> groupedStream.count() > > >>>>> .withStoreName("name") > > >>>>> .withCachingEnabled(false) > > >>>>> .withLoggingEnabled(config) > > >>>>> .table() > > >>>>> > > >>>>> > > >>>>> > > >>>>> Another option would be to provide a Builder to the count method, > so > > it > > >>>>> would look something like this: > > >>>>> groupedStream.count(new > > >>>>> CountBuilder("storeName").withCachingEnabled(false).build()) > > >>>>> > > >>>>> Another option is to say: Hey we don't need this, what are you on > > >> about! > > >>>>> > > >>>>> The above has focussed on state store related overloads, but the > same > > >>>> ideas > > >>>>> could be applied to joins etc, where we presently have many join > > >> methods > > >>>>> and many overloads. > > >>>>> > > >>>>> Anyway, i look forward to hearing your opinions. > > >>>>> > > >>>>> Thanks, > > >>>>> Damian > > >>>>> > > >>>> > > >>> > > >> > > >> > > > > > > > > > > -- > -- Guozhang >
