Hi All, While working on the implementation of KIP-479, some issues came to light that the KIP as written won't work. I have updated the KIP with a solution I believe will solve the original problem as well as address the impediment to the initial approach.
This update is a significant change, so please review the updated KIP https://cwiki.apache.org/confluence/display/KAFKA/KIP-479%3A+Add+StreamJoined+config+object+to+Join and provide feedback. After we conclude the discussion, there will be a re-vote. Thanks! Bill On Wed, Jul 17, 2019 at 7:01 PM Guozhang Wang <wangg...@gmail.com> wrote: > Hi Bill, thanks for your explanations. I'm on board with your decision too. > > > Guozhang > > On Wed, Jul 17, 2019 at 10:20 AM Bill Bejeck <bbej...@gmail.com> wrote: > > > Thanks for the response, John. > > > > > If I can offer my thoughts, it seems better to just document on the > > > Stream join javadoc for the Materialized parameter that it will not > > > make the join result queriable. I'm not opposed to the queriable flag > > > in general, but introducing it is a much larger consideration that has > > > previously derailed this KIP discussion. In the interest of just > > > closing the gap and keeping the API change small, it seems better to > > > just go with documentation for now. > > > > I agree with your statement here. IMHO the most important goal of this > KIP > > is to not breaking existing users and gain some consistency of the API. > > > > I'll update the KIP accordingly. > > > > -Bill > > > > On Tue, Jul 16, 2019 at 11:55 AM John Roesler <j...@confluent.io> wrote: > > > > > Hi Bill, > > > > > > Thanks for driving this KIP toward a conclusion. I'm on board with > > > your decision. > > > > > > You didn't mention whether you're still proposing to add the > > > "queriable" flag to the Materialized config object, or just document > > > that a Stream join is never queriable. Both options have come up > > > earlier in the discussion, so it would be good to pin this down. > > > > > > If I can offer my thoughts, it seems better to just document on the > > > Stream join javadoc for the Materialized parameter that it will not > > > make the join result queriable. I'm not opposed to the queriable flag > > > in general, but introducing it is a much larger consideration that has > > > previously derailed this KIP discussion. In the interest of just > > > closing the gap and keeping the API change small, it seems better to > > > just go with documentation for now. > > > > > > Thanks again, > > > -John > > > > > > On Thu, Jul 11, 2019 at 2:45 PM Bill Bejeck <bbej...@gmail.com> wrote: > > > > > > > > Thanks all for the great discussion so far. > > > > > > > > Everyone has made excellent points, and I appreciate the detail > > everyone > > > > has put into their arguments. > > > > > > > > However, after carefully evaluating all the points made so far, > > creating > > > an > > > > overload with Materialized is still my #1 option. > > > > My reasoning for saying so is two-fold: > > > > > > > > 1. It's a small change, and IMHO since it's consistent with our > > > current > > > > API concerning state store usage, the cognitive load on users will > > be > > > > minimal. > > > > 2. It achieves the most important goal of this KIP, namely to > close > > > the > > > > gap of naming state stores independently of the join operator > name. > > > > > > > > Additionally, I agree with the points made by Matthias earlier (I > > realize > > > > there is some overlap here). > > > > > > > > > - the main purpose of this KIP is to close the naming gap what we > > > achieve > > > > > - we can allow people to use the new in-memory store > > > > > - we allow people to enable/disable caching > > > > > - we unify the API > > > > > - we decouple querying from naming > > > > > - it's a small API change > > > > > > > > Although it's not a perfect solution, IMHO the positives of using > > > > Materialize far outweigh the negatives, and from what we've discussed > > so > > > > far, anything we implement seems to involve an additional change down > > the > > > > road. > > > > > > > > If others are still strongly opposed to using Materialized, my other > > > > preferences would be > > > > > > > > 1. Add a "withStoreName" to Joined. Although I agree with > Guozhang > > > that > > > > having a parameter that only applies to one use-case would be > > clumsy. > > > > 2. Add a String overload for naming the store, but this would be > my > > > > least favorite option as IMHO this seems to be a step backward > from > > > why we > > > > introduced configuration objects in the first place. > > > > > > > > Thanks, > > > > Bill > > > > > > > > On Thu, Jun 27, 2019 at 4:45 PM Matthias J. Sax < > matth...@confluent.io > > > > > > > wrote: > > > > > > > > > Thanks for the KIP Bill! > > > > > > > > > > Great discussion to far. > > > > > > > > > > About John's idea about querying upstream stores and don't > > materialize > > > a > > > > > store: I agree with Bill that this seems to be an orthogonal > > question, > > > > > and it might be better to treat it as an independent optimization > and > > > > > exclude from this KIP. > > > > > > > > > > > What should be the behavior if there is no store > > > > > > configured (e.g., if Materialized with only serdes) and querying > is > > > > > > enabled? > > > > > > > > > > IMHO, this could be an error case. If one wants to query a store, > > they > > > > > need to provide a name -- if you don't know the name, how would you > > > > > actually query the store (even if it would be possible to get the > > name > > > > > from the `TopologyDescription`, it seems clumsy). > > > > > > > > > > If we don't want to throw an error, materializing seems to be the > > right > > > > > option, to exclude "query optimization" from this KIP. I would be > ok > > > > > with this option, even if it's clumsy to get the name from > > > > > `TopologyDescription`; hence, I would prefer to treat it as an > error. > > > > > > > > > > > To get back to the current behavior, users would have to > > > > > > add a "bytes store supplier" to the Materialized to indicate > that, > > > > > > yes, they really want a state store there. > > > > > > > > > > This sound like a quite subtle semantic difference on how to use > the > > > > > API. Might be hard to explain to users. I would prefer to not > > > introduce it. > > > > > > > > > > > > > > > > > > > > About Guozhang's points: > > > > > > > > > > 1a) That is actually a good point. However, I believe we cannot get > > > > > around this issue easily, and it seems ok to me, to expose the > actual > > > > > store type we are using. (More thoughts later.) > > > > > > > > > > 1b) I don't see an issue with allowing users to query all stores? > > What > > > > > is the rational behind it? What do we gain by not allowing it? > > > > > > > > > > 2) While I understand what you are saying, we also want/need to > have > > a > > > > > way in the PAPI to allow users adding "internal/private" > > non-queryable > > > > > stores to a topology. That's possible via > > > > > `Materialized#withQueryingDisabled()`. We could also update > > > > > `Topology#addStateStore(StoreBuilder, boolean isQueryable, > > String...)` > > > > > to address this. Again, I agree with Bill that the current API is > > built > > > > > in a certain way, and if we want to change it, it should be a > > separate > > > > > KIP, as it seems to be an orthogonal concern. > > > > > > > > > > > Instead, we just restrict KIP-307 to NOT > > > > > > use the Joined.name for state store names and always use internal > > > names > > > > > as > > > > > > well, which admittedly indeed leaves a hole of not being able to > > > cover > > > > > all > > > > > > internal names here > > > > > > > > > > I think it's important to close this gap. Naming entities seems to > a > > > > > binary feature: if there is a gap, the feature is more or less > > useless, > > > > > rendering KIP-307 void. > > > > > > > > > > > > > > > > > > > > I like John's detailed list of required features and what > > > > > Materialized/WindowByteStoreSuppliers offers. My take is, that > adding > > > > > Materialized including the required run-time checks is the best > > option > > > > > we have, for the following reasons: > > > > > > > > > > - the main purpose of this KIP is to close the naming gap what we > > > achieve > > > > > - we can allow people to use the new in-memory store > > > > > - we allow people to enable/disable caching > > > > > - we unify the API > > > > > - we decouple querying from naming > > > > > - it's a small API change > > > > > > > > > > Adding an overload and only passing in a name, would address the > main > > > > > purpose of the KIP. However, it falls short on all the other > > "goodies". > > > > > As you mentioned, passing in `Materialized` might not be perfect > and > > > > > maybe we need to deprecate is at some point; but this is also true > > for > > > > > passing in just a name. > > > > > > > > > > I am also not convinced, that a `StreamJoinStore` would resolve all > > the > > > > > issues. In the end, as long as we are using a `WindowedStore` > > > > > internally, we need to expose this "implemenation detail" to users > to > > > > > allow them to plug in a custom store. Adding `Materialized` seem to > > be > > > > > the best short-term fix from my point of view. > > > > > > > > > > > > > > > -Matthias > > > > > > > > > > > > > > > On 6/27/19 9:56 AM, Guozhang Wang wrote: > > > > > > Hi John, > > > > > > > > > > > > I actually feels better about a new interface but I'm not sure if > > we > > > > > would > > > > > > need the full configuration of store / log / cache, now or in the > > > future > > > > > > ever for stream-stream join. > > > > > > > > > > > > Right now I feel that 1) we want to improve our implementation of > > > > > > stream-stream join, and potentially also allow users to customize > > > this > > > > > > implementation but with a more suitable interface than the > current > > > > > > WindowStore interface, how to do that is less clear and > > > execution-wise > > > > > it's > > > > > > (arguably..) not urgent; 2) we want to close the last gap > > > (Stream-stream > > > > > > join) of allowing users to specify all internal names to help on > > > backward > > > > > > compatibility, which is urgent. > > > > > > > > > > > > Therefore if we want to unblock 2) from 1) in the near term, I > feel > > > > > > slightly inclined to just add overload functions that takes in a > > > store > > > > > name > > > > > > for stream-stream joins only -- and admittedly, in the future > this > > > > > function > > > > > > maybe deprecated -- i.e. if we have to do something that we "may > > > regret" > > > > > in > > > > > > the future, I'd like to pick the least intrusive option. > > > > > > > > > > > > About `Joined#withStoreName`: since the Joined class itself is > also > > > used > > > > > in > > > > > > other join types, I feel less comfortable to have a > > > > > `Joined#withStoreName` > > > > > > which is only going to be used by stream-stream join. Or maybe I > > miss > > > > > > something here about the "latter" case that you are referring to? > > > > > > > > > > > > > > > > > > > > > > > > Guozhang > > > > > > > > > > > > On Mon, Jun 24, 2019 at 12:16 PM John Roesler <j...@confluent.io > > > > > wrote: > > > > > > > > > > > >> Thanks Guozhang, > > > > > >> > > > > > >> Yep. Maybe we can consider just exactly what the join needs: > > > > > >> > > > > > >>> the WindowStore<Bytes, byte[]> itself is fine, if overly broad, > > > > > >>> since the only two methods we need are `window.put(key, value, > > > > > >>> context().timestamp())` and `WindowStoreIterator<V2> iter = > > > > > >>> window.fetch(key, timeFrom, timeTo)`. > > > > > >> > > > > > >> One "middle ground" would be to extract _this_ into a new store > > > > > >> interface, which only supports these API calls, like > > > > > >> StreamJoinStore<K, V>. This would give us the latitude we need > to > > > > > >> efficiently support the exact operation without concerning > > ourselves > > > > > >> with all the other things a WindowStore can do (which are > > > unreachable > > > > > >> for the join use case). It would also let us drop "store > > duplicates" > > > > > >> from the main WindowStore interface, since it only exists to > > support > > > > > >> the join use case. > > > > > >> > > > > > >> If we were to add a new StreamJoinStore interface, then it'd be > > > > > >> straightforward how we could add also > > > > > >> `Materialized.as(StreamJoinBytesStoreSupplier)` and use > > > Materialized, > > > > > >> or alternatively add the ability to set the bytes store on > Joined. > > > > > >> > > > > > >> Personally, I'm kind of leaning toward the latter (and also > doing > > > > > >> `Joined#withStoreName`), since adding the new interface to > > > > > >> Materialized then also pollutes the interface for its _actual_ > use > > > > > >> case of materializing a table view. Of course, to solve the > > > immediate > > > > > >> problem, all we need is the store name, but we might feel better > > > about > > > > > >> adding the store name to Joined if we _also_ feel like in the > > > future, > > > > > >> we would add store/log/cache configuration to Joined as well. > > > > > >> > > > > > >> -John > > > > > >> > > > > > >> On Mon, Jun 24, 2019 at 12:56 PM Guozhang Wang < > > wangg...@gmail.com> > > > > > wrote: > > > > > >>> > > > > > >>> Hello John, > > > > > >>> > > > > > >>> My main concern is exactly the first point at the bottom of > your > > > > > analysis > > > > > >>> here: "* configure the bytes store". I'm not sure if using a > > window > > > > > bytes > > > > > >>> store would be ideal for stream-stream windowed join; e.g. we > > could > > > > > >>> consider two dimensional list sorted by timestamps and then by > > > keys to > > > > > do > > > > > >>> the join, whereas a windowed bytes store is basically sorted by > > key > > > > > >> first, > > > > > >>> then by timestamp. If we expose the Materialized to let user > pass > > > in a > > > > > >>> windowed bytes store, then we would need to change that if we > > want > > > to > > > > > >>> replace it with a different implementation interface. > > > > > >>> > > > > > >>> > > > > > >>> Guozhang > > > > > >>> > > > > > >>> On Mon, Jun 24, 2019 at 8:59 AM John Roesler < > j...@confluent.io> > > > > > wrote: > > > > > >>> > > > > > >>>> Hey Guozhang and Bill, > > > > > >>>> > > > > > >>>> For what it's worth, I agree with you both! > > > > > >>>> > > > > > >>>> I think it might help the discussion to look concretely at > what > > > > > >>>> Materialized does: > > > > > >>>> * set a WindowBytesStoreSupplier > > > > > >>>> * set a name > > > > > >>>> * set the key/value serdes > > > > > >>>> * disable/enable/configure change-logging > > > > > >>>> * disable/enable caching > > > > > >>>> * configure retention > > > > > >>>> > > > > > >>>> Further, looking into the WindowBytesStoreSupplier, the > > interface > > > lets > > > > > >> you: > > > > > >>>> * get the segment interval > > > > > >>>> * get the window size > > > > > >>>> * get whether "duplicates" are enabled > > > > > >>>> * get the retention period > > > > > >>>> * (obviously) get a WindowStore<Bytes, byte[]> > > > > > >>>> > > > > > >>>> We know that Materialized isn't exactly what we need for > stream > > > joins, > > > > > >>>> but we can see how close Materialized is to what we need. If > it > > is > > > > > >>>> close, maybe we can use it and document the gaps, and if it is > > not > > > > > >>>> close, then maybe we should just add what we need to Joined. > > > > > >>>> Stream Join's requirements for its stores: > > > > > >>>> * a multimap store (i.e., it keeps duplicates) for storing > > general > > > > > >>>> (not windowed) keyed records associated with their insertion > > > time, and > > > > > >>>> allows efficient time-bounded lookups and also efficient > purges > > > of old > > > > > >>>> data. > > > > > >>>> ** Note, a properly configured WindowBytesStoreSupplier > > satisfies > > > this > > > > > >>>> requirement, and the interface supports the queries we need to > > > verify > > > > > >>>> the configuration at run-time > > > > > >>>> * set a name for the store > > > > > >>>> * do _not_ set the serdes (they are already set in Joined) > > > > > >>>> * logging could be configurable (set to enabled now) > > > > > >>>> * caching could be configurable (set to enabled now) > > > > > >>>> * do _not_ configure retention (determined by JoinWindows) > > > > > >>>> > > > > > >>>> So, out of six capabilities for Materialized, there are two we > > > don't > > > > > >>>> want (serdes and retention). These would become run-time > checks > > > if we > > > > > >>>> use it. > > > > > >>>> > > > > > >>>> A third questionable capability is to provide a > > > > > >>>> WindowBytesStoreSupplier. Looking at whether the > > > > > >>>> WindowBytesStoreSupplier is the right interface for Stream > Join: > > > > > >>>> * configuring segment interval is fine > > > > > >>>> * should _not_ configure window size (it's determined by > > > JoinWindows) > > > > > >>>> * duplicates _must_ be enabled > > > > > >>>> * retention should be _at least_ windowSize + gracePeriod, but > > > note > > > > > >>>> that (unlike for Table window stores) there is no utility in > > > having a > > > > > >>>> longer retention time. > > > > > >>>> * the WindowStore<Bytes, byte[]> itself is fine, if overly > > broad, > > > > > >>>> since the only two methods we need are `window.put(key, value, > > > > > >>>> context().timestamp())` and `WindowStoreIterator<V2> iter = > > > > > >>>> window.fetch(key, timeFrom, timeTo)`. > > > > > >>>> > > > > > >>>> Thus, flattening out the overlap for WindowBytesStoreSupplier > > > onto the > > > > > >>>> overlap for Materialized, we have 9 capabilities total (note > > > retention > > > > > >>>> is duplicated), we have 4 that we don't want: > > > > > >>>> * do _not_ set the serdes (they are already set in Joined) > > > > > >>>> * do _not_ configure retention (determined by JoinWindows) > > > > > >>>> * should _not_ configure window size (it's determined by > > > JoinWindows) > > > > > >>>> * duplicates _must_ be enabled > > > > > >>>> > > > > > >>>> These gaps would have to be covered with run-time checks if we > > > re-use > > > > > >>>> Materialized and WindowStoreBytesStoreSupplier both. Maybe > this > > > sounds > > > > > >>>> bad, but consider the other side, that we get 5 new > capabilities > > > we > > > > > >>>> don't require, but are still pretty nice: > > > > > >>>> * configure the bytes store > > > > > >>>> * set a name for the store > > > > > >>>> * configure caching > > > > > >>>> * configure logging > > > > > >>>> * configure segment interval > > > > > >>>> > > > > > >>>> Not sure where this nets us out, but it's food for thought. > > > > > >>>> -John > > > > > >>>> > > > > > >>>> On Sun, Jun 23, 2019 at 7:52 PM Guozhang Wang < > > wangg...@gmail.com > > > > > > > > > >> wrote: > > > > > >>>>> > > > > > >>>>> Hi Bill, > > > > > >>>>> > > > > > >>>>> I think by giving a Materialized param into stream-stream > join, > > > it's > > > > > >> okay > > > > > >>>>> (though still ideal) to say "we still would not expose the > > store > > > for > > > > > >>>>> queries", but it would sound a bit awkward to say "we would > > also > > > > > >> ignore > > > > > >>>>> whatever the passed in store supplier but just use our > default > > > ones" > > > > > >> -- > > > > > >>>>> again the concern is that, if in the future we'd want to > change > > > the > > > > > >>>> default > > > > > >>>>> implementation of join algorithm which no longer rely on a > > window > > > > > >> store > > > > > >>>>> with deduping enabled, then we need to change this API again > by > > > > > >> changing > > > > > >>>>> the store supplier type. > > > > > >>>>> > > > > > >>>>> If we do want to fill this hole for stream-stream join, I > feel > > > just > > > > > >>>> adding > > > > > >>>>> a String typed store-name would even be less future-intrusive > > if > > > we > > > > > >>>> expect > > > > > >>>>> this parameter to be modified later. > > > > > >>>>> > > > > > >>>>> Does that makes sense? > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> Guozhang > > > > > >>>>> > > > > > >>>>> On Sat, Jun 22, 2019 at 12:51 PM Bill Bejeck < > > bbej...@gmail.com> > > > > > >> wrote: > > > > > >>>>> > > > > > >>>>>> Thanks for the comments John and Guozhang, I'll address each > > > one of > > > > > >>>> your > > > > > >>>>>> comments in turn. > > > > > >>>>>> > > > > > >>>>>> John, > > > > > >>>>>> > > > > > >>>>>>> I'm wondering about a missing quadrant from the truth table > > > > > >> involving > > > > > >>>>>>> whether a Materialized is stored or not and querying is > > > > > >>>>>>> enabled/disabled... What should be the behavior if there is > > no > > > > > >> store > > > > > >>>>>>> configured (e.g., if Materialized with only serdes) and > > > querying > > > > > >> is > > > > > >>>>>> enabled? > > > > > >>>>>> > > > > > >>>>>>> It seems we have two choices: > > > > > >>>>>>> 1. we can force creation of a state store in this case, so > > the > > > > > >> store > > > > > >>>>>>> can be used to serve the queries > > > > > >>>>>>> 2. we can provide just a queriable view, basically letting > IQ > > > > > >> query > > > > > >>>>>>> into the "KTableValueGetter", which would transparently > > > > > >> construct the > > > > > >>>>>>> query response by applying the operator logic to the > upstream > > > > > >> state > > > > > >>>> if > > > > > >>>>>>> the operator state isn't already stored. > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> I agree with your assertion about a missing quadrant from > the > > > truth > > > > > >>>> table. > > > > > >>>>>> Additionally, I too like the concept of a queriable view. > > But I > > > > > >> think > > > > > >>>> that > > > > > >>>>>> goes a bit beyond the scope of this KIP and would like to > > pursue > > > > > >> that > > > > > >>>>>> feature as follow-on work. Also thinking about this KIP > some > > > > > >> more, I'm > > > > > >>>>>> thinking of the changes to Materialized might be a reach as > > > well. > > > > > >>>>>> Separating the naming from a store and its queryable state > > seems > > > > > >> like a > > > > > >>>>>> complex issue in and of itself and should be treated > > > accordingly. > > > > > >>>>>> > > > > > >>>>>> So here's what I'm thinking now. We add Materialzied to > Join, > > > but > > > > > >> for > > > > > >>>> now, > > > > > >>>>>> we internally disable querying. I know this breaks our > > current > > > > > >>>> semantic > > > > > >>>>>> approach, but I think it's crucial that we do two things in > > this > > > > > >> KIP > > > > > >>>>>> > > > > > >>>>>> 1. Break the naming of the state stores from Joined to > > > > > >>>> Materialized, so > > > > > >>>>>> the naming of state stores follows our current pattern > and > > > > > >> enables > > > > > >>>>>> upgrades > > > > > >>>>>> from 2.3 to 2.4 > > > > > >>>>>> 2. Offer the ability to configure the state stores of the > > > join, > > > > > >> even > > > > > >>>>>> providing a different implementation (i.e. in-memory) if > > > > > >> desired. > > > > > >>>>>> > > > > > >>>>>> With that in mind I'm considering changing the KIP to remove > > the > > > > > >>>> changes to > > > > > >>>>>> Materialized, and we document very clearly that by > providing a > > > > > >>>> Materialized > > > > > >>>>>> object with a name is only for naming the state store, hence > > the > > > > > >>>> changelog > > > > > >>>>>> topics and any possible configurations of the store, but > this > > > store > > > > > >>>> *will > > > > > >>>>>> not be available for IQ.* > > > > > >>>>>> > > > > > >>>>>> WDYT? > > > > > >>>>>> > > > > > >>>>>> Guozhang, > > > > > >>>>>> > > > > > >>>>>>> 1. About not breaking compatibility of stream-stream join > > > > > >>>> materialized > > > > > >>>>>>> stores: I think this is a valid issue to tackle, but after > > > > > >> thinking > > > > > >>>> about > > > > > >>>>>>> it once more I'm not sure if exposing Materialized would > be a > > > > > >> good > > > > > >>>>>> solution > > > > > >>>>>>> here. My rationles: > > > > > >>>>>>> > > > > > >>>>>>> 1.a For stream-stream join, our current usage of > window-store > > > is > > > > > >> not > > > > > >>>>>> ideal, > > > > > >>>>>>> and we want to modify it in the near future to be more > > > > > >> efficient. Not > > > > > >>>>>>> allowing users to override such state store backend gives > us > > > such > > > > > >>>> freedom > > > > > >>>>>>> (which was also considered in the original DSL design), > > whereas > > > > > >>>> getting a > > > > > >>>>>>> Materialized<WindowStore> basically kicks out that freedom > > out > > > > > >> of the > > > > > >>>>>>> window. > > > > > >>>>>>> 1.b For strema-stream join, in our original design we > intend > > to > > > > > >>>> "never" > > > > > >>>>>>> want users to query the state, since it is just for > buffering > > > the > > > > > >>>>>> upcoming > > > > > >>>>>>> records from the stream. Now I know that some users may > > indeed > > > > > >> want > > > > > >>>> to > > > > > >>>>>>> query it from the debugging perspective, but still I > > concerned > > > > > >> about > > > > > >>>>>>> whether leveraging IQ for debugging purposes would be the > > right > > > > > >>>> solution > > > > > >>>>>>> here. And adding Materialized object opens the door to let > > > users > > > > > >>>> query > > > > > >>>>>>> about it (unless we did something intentionally to still > > > forbids > > > > > >> it), > > > > > >>>>>> which > > > > > >>>>>>> also restricts us in the future. > > > > > >>>>>>> > > > > > >>>>>>> 2. About the coupling between Materialized.name() and > > > queryable: > > > > > >>>> again I > > > > > >>>>>>> think this is a valid issue. But I'm not sure if the > current > > > > > >>>>>>> "withQuerryingDisabled / Enabled" at Materialized is the > best > > > > > >>>> approach. > > > > > >>>>>>> Here I think I agree with John, that generally speaking > it's > > > > > >> better > > > > > >>>> be a > > > > > >>>>>>> control function on the `KTable` itself, rather than on > > > > > >>>> `Materialized`, > > > > > >>>>>> so > > > > > >>>>>>> fixing it via adding functions through `Materialized` seems > > > not a > > > > > >>>> natural > > > > > >>>>>> approach either. > > > > > >>>>>> > > > > > >>>>>> I understand your thoughts here, and up to a point, I agree > > with > > > > > >> you. > > > > > >>>>>> But concerning not providing Materialized as it may restrict > > us > > > in > > > > > >> the > > > > > >>>>>> future for delivering different implementations, I'm > wondering > > > if > > > > > >> we > > > > > >>>> are > > > > > >>>>>> doing some premature optimization here. > > > > > >>>>>> My rationale for saying so > > > > > >>>>>> > > > > > >>>>>> 1. I think the cost of not allowing the naming of state > > > stores > > > > > >> for > > > > > >>>> joins > > > > > >>>>>> is too big of a gap to leave. IMHO for joins to follow > > the > > > > > >> current > > > > > >>>>>> pattern of using Materialized for naming state stores > would > > > be > > > > > >> what > > > > > >>>> most > > > > > >>>>>> users would expect to use. As I said in my comments > > above, I > > > > > >> think > > > > > >>>> we > > > > > >>>>>> should *not include* the changes to Materialized and > > enforce > > > > > >> named > > > > > >>>>>> stores for joins as unavailable for IQ. > > > > > >>>>>> 2. We'll still have the join methods available without a > > > > > >>>> Materialized > > > > > >>>>>> allowing us to do something different internally if a > > > > > >> Materialized > > > > > >>>> is > > > > > >>>>>> not > > > > > >>>>>> provided. > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>>> Overall, I'm thinking maybe we should still use two stones > > > rather > > > > > >>>> than > > > > > >>>>>> one > > > > > >>>>>>> to kill these two birds, and probably for this KIP we just > > > focus > > > > > >> on > > > > > >>>> 1) > > > > > >>>>>>> above. And for that I'd like to not expose the Materialized > > > > > >> either > > > > > >>>> for > > > > > >>>>>>> rationales that I've listed above. Instead, we just > restrict > > > > > >> KIP-307 > > > > > >>>> to > > > > > >>>>>> NOT > > > > > >>>>>>> use the Joined.name for state store names and always use > > > internal > > > > > >>>> names > > > > > >>>>>> as > > > > > >>>>>>> well, which admittedly indeed leaves a hole of not being > able > > > to > > > > > >>>> cover > > > > > >>>>>> all > > > > > >>>>>>> internal names here, but now I feel this `hole` may better > be > > > > > >> filled > > > > > >>>> by, > > > > > >>>>>>> e.g. not creating changelog topics but just use the > upstream > > to > > > > > >>>>>>> re-bootstrap the materialized store, more concretely: when > > > > > >>>> materializing > > > > > >>>>>>> the store, try to piggy-back the changelog topic on an > > existing > > > > > >>>> topic, > > > > > >>>>>> e.g. > > > > > >>>>>>> a) if the stream is coming directly from some source topic > > > > > >> (including > > > > > >>>>>>> repartition topic), make that as changelog topic and if it > is > > > > > >>>> repartition > > > > > >>>>>>> topic change the retention / data purging policy > necessarily > > as > > > > > >>>> well; b) > > > > > >>>>>> if > > > > > >>>>>>> the stream is coming from some stateless operators, > delegate > > > that > > > > > >>>>>> stateless > > > > > >>>>>>> operator to the parent stream similar as a); if the stream > is > > > > > >> coming > > > > > >>>> from > > > > > >>>>>> a > > > > > >>>>>>> stream-stream join which is the only stateful operator that > > can > > > > > >>>> result in > > > > > >>>>>> a > > > > > >>>>>>> stream, consider merging the join into multi-way joins > (yes, > > > > > >> this is > > > > > >>>> a > > > > > >>>>>> very > > > > > >>>>>>> hand-wavy thought, but the point here is that we do not try > > to > > > > > >>>> tackle it > > > > > >>>>>>> now but leave it for a better solution :). > > > > > >>>>>> > > > > > >>>>>> I really like this idea! I agree with you in that this > > approach > > > > > >> to too > > > > > >>>>>> much for adding in this KIP, but we could pick it up later > and > > > > > >>>> leverage the > > > > > >>>>>> Optimization framework to accomplish this re-use. > > > > > >>>>>> Again, while I agree we should break the naming of join > state > > > > > >> stores > > > > > >>>> from > > > > > >>>>>> KIP-307, IMHO it's something we should fix now as it will be > > the > > > > > >> last > > > > > >>>> piece > > > > > >>>>>> we can provide to give users the ability to completely make > > > their > > > > > >>>>>> topologies "upgrade proof" when adding additional > operations. > > > > > >>>>>> > > > > > >>>>>> Thanks again to both of you for comments and I look forward > to > > > > > >> hearing > > > > > >>>> back > > > > > >>>>>> from you. > > > > > >>>>>> > > > > > >>>>>> Regards, > > > > > >>>>>> Bill > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> > > > > > >>>>>> On Thu, Jun 20, 2019 at 2:33 PM Guozhang Wang < > > > wangg...@gmail.com> > > > > > >>>> wrote: > > > > > >>>>>> > > > > > >>>>>>> Hello Bill, > > > > > >>>>>>> > > > > > >>>>>>> Thanks for the KIP. Glad to see that we can likely shooting > > two > > > > > >> birds > > > > > >>>>>> with > > > > > >>>>>>> one stone. I have some concerns though about those "two > > birds" > > > > > >>>>>> themselves: > > > > > >>>>>>> > > > > > >>>>>>> 1. About not breaking compatibility of stream-stream join > > > > > >>>> materialized > > > > > >>>>>>> stores: I think this is a valid issue to tackle, but after > > > > > >> thinking > > > > > >>>> about > > > > > >>>>>>> it once more I'm not sure if exposing Materialized would > be a > > > > > >> good > > > > > >>>>>> solution > > > > > >>>>>>> here. My rationles: > > > > > >>>>>>> > > > > > >>>>>>> 1.a For stream-stream join, our current usage of > window-store > > > is > > > > > >> not > > > > > >>>>>> ideal, > > > > > >>>>>>> and we want to modify it in the near future to be more > > > > > >> efficient. Not > > > > > >>>>>>> allowing users to override such state store backend gives > us > > > such > > > > > >>>> freedom > > > > > >>>>>>> (which was also considered in the original DSL design), > > whereas > > > > > >>>> getting a > > > > > >>>>>>> Materialized<WindowStore> basically kicks out that freedom > > out > > > > > >> of the > > > > > >>>>>>> window. > > > > > >>>>>>> 1.b For strema-stream join, in our original design we > intend > > to > > > > > >>>> "never" > > > > > >>>>>>> want users to query the state, since it is just for > buffering > > > the > > > > > >>>>>> upcoming > > > > > >>>>>>> records from the stream. Now I know that some users may > > indeed > > > > > >> want > > > > > >>>> to > > > > > >>>>>>> query it from the debugging perspective, but still I > > concerned > > > > > >> about > > > > > >>>>>>> whether leveraging IQ for debugging purposes would be the > > right > > > > > >>>> solution > > > > > >>>>>>> here. And adding Materialized object opens the door to let > > > users > > > > > >>>> query > > > > > >>>>>>> about it (unless we did something intentionally to still > > > forbids > > > > > >> it), > > > > > >>>>>> which > > > > > >>>>>>> also restricts us in the future. > > > > > >>>>>>> > > > > > >>>>>>> 2. About the coupling between Materialized.name() and > > > queryable: > > > > > >>>> again I > > > > > >>>>>>> think this is a valid issue. But I'm not sure if the > current > > > > > >>>>>>> "withQuerryingDisabled / Enabled" at Materialized is the > best > > > > > >>>> approach. > > > > > >>>>>>> Here I think I agree with John, that generally speaking > it's > > > > > >> better > > > > > >>>> be a > > > > > >>>>>>> control function on the `KTable` itself, rather than on > > > > > >>>> `Materialized`, > > > > > >>>>>> so > > > > > >>>>>>> fixing it via adding functions through `Materialized` seems > > > not a > > > > > >>>> natural > > > > > >>>>>>> approach either. > > > > > >>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> Overall, I'm thinking maybe we should still use two stones > > > rather > > > > > >>>> than > > > > > >>>>>> one > > > > > >>>>>>> to kill these two birds, and probably for this KIP we just > > > focus > > > > > >> on > > > > > >>>> 1) > > > > > >>>>>>> above. And for that I'd like to not expose the Materialized > > > > > >> either > > > > > >>>> for > > > > > >>>>>>> rationales that I've listed above. Instead, we just > restrict > > > > > >> KIP-307 > > > > > >>>> to > > > > > >>>>>> NOT > > > > > >>>>>>> use the Joined.name for state store names and always use > > > internal > > > > > >>>> names > > > > > >>>>>> as > > > > > >>>>>>> well, which admittedly indeed leaves a hole of not being > able > > > to > > > > > >>>> cover > > > > > >>>>>> all > > > > > >>>>>>> internal names here, but now I feel this `hole` may better > be > > > > > >> filled > > > > > >>>> by, > > > > > >>>>>>> e.g. not creating changelog topics but just use the > upstream > > to > > > > > >>>>>>> re-bootstrap the materialized store, more concretely: when > > > > > >>>> materializing > > > > > >>>>>>> the store, try to piggy-back the changelog topic on an > > existing > > > > > >>>> topic, > > > > > >>>>>> e.g. > > > > > >>>>>>> a) if the stream is coming directly from some source topic > > > > > >> (including > > > > > >>>>>>> repartition topic), make that as changelog topic and if it > is > > > > > >>>> repartition > > > > > >>>>>>> topic change the retention / data purging policy > necessarily > > as > > > > > >>>> well; b) > > > > > >>>>>> if > > > > > >>>>>>> the stream is coming from some stateless operators, > delegate > > > that > > > > > >>>>>> stateless > > > > > >>>>>>> operator to the parent stream similar as a); if the stream > is > > > > > >> coming > > > > > >>>>>> from a > > > > > >>>>>>> stream-stream join which is the only stateful operator that > > can > > > > > >>>> result > > > > > >>>>>> in a > > > > > >>>>>>> stream, consider merging the join into multi-way joins > (yes, > > > > > >> this is > > > > > >>>> a > > > > > >>>>>> very > > > > > >>>>>>> hand-wavy thought, but the point here is that we do not try > > to > > > > > >>>> tackle it > > > > > >>>>>>> now but leave it for a better solution :). > > > > > >>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> Guozhang > > > > > >>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> On Wed, Jun 19, 2019 at 11:41 AM John Roesler < > > > j...@confluent.io > > > > > >>> > > > > > >>>> wrote: > > > > > >>>>>>> > > > > > >>>>>>>> Hi Bill, > > > > > >>>>>>>> > > > > > >>>>>>>> Thanks for the KIP! Awesome job catching this unexpected > > > > > >>>> consequence > > > > > >>>>>>>> of the prior KIPs before it was released. > > > > > >>>>>>>> > > > > > >>>>>>>> The proposal looks good to me. On top of just fixing the > > > > > >> problem, > > > > > >>>> it > > > > > >>>>>>>> seems to address two other pain points: > > > > > >>>>>>>> * that naming a state store automatically causes it to > > become > > > > > >>>>>> queriable. > > > > > >>>>>>>> * that there's currently no way to configure the bytes > store > > > > > >> for > > > > > >>>> join > > > > > >>>>>>>> windows. > > > > > >>>>>>>> > > > > > >>>>>>>> It's awesome that we can fix this issue and two others > with > > > one > > > > > >>>>>> feature. > > > > > >>>>>>>> > > > > > >>>>>>>> I'm wondering about a missing quadrant from the truth > table > > > > > >>>> involving > > > > > >>>>>>>> whether a Materialized is stored or not and querying is > > > > > >>>>>>>> enabled/disabled... What should be the behavior if there > is > > no > > > > > >>>> store > > > > > >>>>>>>> configured (e.g., if Materialized with only serdes) and > > > > > >> querying is > > > > > >>>>>>>> enabled? > > > > > >>>>>>>> > > > > > >>>>>>>> It seems we have two choices: > > > > > >>>>>>>> 1. we can force creation of a state store in this case, so > > the > > > > > >>>> store > > > > > >>>>>>>> can be used to serve the queries > > > > > >>>>>>>> 2. we can provide just a queriable view, basically letting > > IQ > > > > > >> query > > > > > >>>>>>>> into the "KTableValueGetter", which would transparently > > > > > >> construct > > > > > >>>> the > > > > > >>>>>>>> query response by applying the operator logic to the > > upstream > > > > > >>>> state if > > > > > >>>>>>>> the operator state isn't already stored. > > > > > >>>>>>>> > > > > > >>>>>>>> Offhand, it seems like the second is actually a pretty > > awesome > > > > > >>>>>>>> capability. But it might have an awkward interaction with > > the > > > > > >>>> current > > > > > >>>>>>>> semantics. Presently, if I provide a > Materialized.withName, > > it > > > > > >>>> implies > > > > > >>>>>>>> that querying should be enabled AND that the view should > > > > > >> actually > > > > > >>>> be > > > > > >>>>>>>> stored in a state store. Under option 2 above, this > behavior > > > > > >> would > > > > > >>>>>>>> change to NOT provision a state store and instead just > > consult > > > > > >> the > > > > > >>>>>>>> ValueGetter. To get back to the current behavior, users > > would > > > > > >> have > > > > > >>>> to > > > > > >>>>>>>> add a "bytes store supplier" to the Materialized to > indicate > > > > > >> that, > > > > > >>>>>>>> yes, they really want a state store there. > > > > > >>>>>>>> > > > > > >>>>>>>> Behavior changes are always kind of scary, but I think in > > this > > > > > >>>> case, > > > > > >>>>>>>> it might actually be preferable. In the event where only > the > > > > > >> name > > > > > >>>> is > > > > > >>>>>>>> provided, it means that people just wanted to make the > > > > > >> operation > > > > > >>>>>>>> result queriable. If we automatically convert this to a > > > > > >> non-stored > > > > > >>>>>>>> view, then simply upgrading results in the same observable > > > > > >> behavior > > > > > >>>>>>>> and semantics, but a linear reduction in local storage > > > > > >> requirements > > > > > >>>>>>>> and disk i/o, as well as a corresponding linear reduction > in > > > > > >> memory > > > > > >>>>>>>> usage both on and off heap. > > > > > >>>>>>>> > > > > > >>>>>>>> What do you think? > > > > > >>>>>>>> -John > > > > > >>>>>>>> > > > > > >>>>>>>> On Tue, Jun 18, 2019 at 9:21 PM Bill Bejeck < > > > bbej...@gmail.com > > > > > >>> > > > > > >>>> wrote: > > > > > >>>>>>>>> > > > > > >>>>>>>>> All, > > > > > >>>>>>>>> > > > > > >>>>>>>>> I'd like to start a discussion for adding a Materialized > > > > > >>>>>> configuration > > > > > >>>>>>>>> object to KStream.join for naming state stores involved > in > > > > > >> joins. > > > > > >>>>>>>>> > > > > > >>>>>>>>> > > > > > >>>>>>>> > > > > > >>>>>>> > > > > > >>>>>> > > > > > >>>> > > > > > >> > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-479%3A+Add+Materialized+to+Join > > > > > >>>>>>>>> > > > > > >>>>>>>>> Your comments and suggestions are welcome. > > > > > >>>>>>>>> > > > > > >>>>>>>>> Thanks, > > > > > >>>>>>>>> Bill > > > > > >>>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> > > > > > >>>>>>> -- > > > > > >>>>>>> -- Guozhang > > > > > >>>>>>> > > > > > >>>>>> > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> -- > > > > > >>>>> -- Guozhang > > > > > >>>> > > > > > >>> > > > > > >>> > > > > > >>> -- > > > > > >>> -- Guozhang > > > > > >> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > -- Guozhang >
