I agree with everything Almog said above, and will just add on to two points:
1. Regarding whether to block this KIP on the completion of any or all future implementations of in-memory version stores (or persist suppression buffers), I feel that would be unfair to this feature which is completely unrelated to the semantic improvements offered by versioned state stores. It seems like the responsibility of those driving the versioned state stores feature, not Almog/this KIP, to make sure that those bases are covered. Further, if anything, this KIP will help with the massive proliferation of StoreSuppliers on the Stores factory class, and provide users with a much easier way to leverage the versioned stores without having to muck around directly with the StoreSuppliers. I also thought about it a bit, and really like Almog's suggestion to introduce an additional StoreSpec for the Versioned state stores. Obviously we can add the RocksDB one to this KIP now, and then as he mentioned, there's an easy way to get users onto the IMVersionedStateStore types once they are completed. Lastly, on this note, I want to point out how smoothly this solved the issue of timestamped stores, which are intended to be the DSL default but are only a special case for RocksDB. Right now it can be confusing for a user scrolling through the endless Stores class and seeing a timestamped version of the persistent but not in-memory stores. One could easily assume there was no timestamped option for IM stores and that this feature was incomplete, if they weren't acutely aware of the internal implementation details (namely that it's only required for RocksDB for compatibility reasons). However, with this KIP, all that is handled completely transparently to the user, and we the devs, who *are* aware of the internal implementation details, are now appropriately the ones responsible for handing the correct store type to a particular operator. While versioned state stores may not be completely comparable, depending on whether we want users to remain able to easily choose between using them or not (vs timestamped which should be used by all), I still feel this KIP is a great step in the right direction that not only should not be blocked on the completion of the IM implementations, but in fact should specifically be done first as it enables an easier way to utilize those IM versioned stores. Just my 2 cents :) 2. The idea to expand the existing the config with a CUSTOM enum without introducing another config to specify the CUSTOM store spec does not seem appropriate, or even possible (for the reasons Almog mentioned above about config types, though perhaps there is a way I'm not seeing). I do not buy the argument that we should optimize the API to make it easy for users who just want to switch to all in-memory stores, as I truly believe this is a very small fraction of the potential userbase of this feature (anyone who's actually using this should please chime in!). It seems very likely that the majority of users of this feature are actually those with custom state stores, as to my knowledge, this has been the case any/every time this feature was requested by users. That said, while I don't see any way to get around introducing a new config, I don't personally have a preference w.r.t whether to keep around the old config or deprecate it. I simply don't get the impression it is very heavily used as it stands today, while it only works for those who want all in-memory stores. Again, input from actual users would be very valuable here. In the absence of that data, I will just point to the fact that this KIP was proposed by a Streams dev (you :P), abandoned, picked up by another Streams dev, and finally implemented without ever hearing from a user that they would find this useful. This is not to disparage the original KIP, but just to say again, as I stated back then, it seemed like a major opportunity loss to leave out custom state stores Cheers, Sophie On Fri, Jul 21, 2023 at 1:52 PM Almog Gavra <almog.ga...@gmail.com> wrote: > Thanks for all the feedback folk! Responses inline. > > > Basically, I'm suggesting two things: first, call out in some way > (perhaps the StoreTypeSpec javadocs) that each StoreTypeSpec is considered > a public contract in itself and should outline any semantic guarantees it > does, or does not, make. Second, we should add a note on ordering > guarantees in the two OOTB specs: for RocksDB we assert that range queries > will honor serialized byte ordering, whereas the InMemory flavor gives no > ordering guarantee whatsoever at this time. > > That makes sense to me Sophie! I'll make the changes to the KIP. And @Colt, > yes I believe that would be the new javadoc for the generic > ReadOnlyKeyValueStore. > > > However, I am wondering if we should close others gaps first? > > @Matthias, thanks for the review and thoughts! I think we should separate > closing other gaps in the product from providing this as useful > functionality to avoid feature creep so long as the API proposed here will > be suitable for when we want to close those implementation gaps! My general > proposal is that for things that are not customizable today by > default.dsl.store they remain not customizable after this KIP. The good > news is, however, that there's no reason why this cannot be extended to > cover those in the future if we want to - see specifics below. > > Comments on the specifics below > > > In particular, this holds for the new versioned-store ... Should > versioned stores also be covered by the KIP > > Is there a reason why we can't introduce a VersionedRocksDBStoreTypeSpec > and if we ever support an in-memory an equivalent > VersionedInMemoryRocksDBStoreTypeSpec? If so, then there would not need to > be any additional changes to the API proposed in this KIP. > > > For `suppress()` it's actually other way around we only have an in-memory > implementation. Do you aim to allow custom stores for `suppress()`, too? > > We have three options here: > 1) we can decide to maintain existing behavior and use the in-memory > implementation for all stores (not even going through the API at all) > 2a) we can introduce a new parameter to the KeyValueParams class (boolean > isTimeOrderedBuffer or something like that) and return an in-memory store > in the implementation of RocksDBStoreTypeSpec (this maintains the existing > behavior, and would allow us in the future to make the change to return a > RocksDB store if we ever provide one) > 2b) same as 2a but we throw an exception if the requested store type does > not support that (this is backwards incompatible, and since ROCKS_DB is the > default we probably shouldn't do this) > > My proposal for now is 1) because as of KIP-825 > EmitStrategy#ON_WINDOW_CLOSE is the preferred way of suppressing and that > is accounted for in this API already. > > > Last, I am not sure if the new parameter replacing the existing one is > the > best way to go? > > I'm happy either way, just let me know which you prefer - the discussion > around CUSTOM is in the rejected alternatives but I'm happy to differ to > whatever the project conventions are :) > > > If it's matches existing `ROCKS_DB` or `IN_MEMORY` we just process it as > we > do know, and if know we assume it's a fully qualified class name and try to > instantiate it? > > Note that there is no functionality for this kind of thing in > AbstractConfig (it's either a String validated enum or a class) so this > would be a departure from convention. Again, I'm happy to implement that if > it's preferred. > > > Also wondering how it would related to the existing `Stores` factory? > > StoreTypeSpec will depend on Stores factory - they're one layer removed. > You can imagine that StoreTypeSpec is just a grouping of methods from the > Stores factory into a convenient package for default configuration > purposes. > > Thanks again for all the detailed thoughts Matthias! > > On Fri, Jul 21, 2023 at 11:50 AM Matthias J. Sax <mj...@apache.org> wrote: > > > Thanks for the KIP. Overall I like the idea to close this gap. > > > > However, I am wondering if we should close others gaps first? In > > particular, IIRC, we have a few cases for which we only have a RocksDB > > implementation for a store, and thus, adding an in-memory version for > > these stores first, to make the current `IN_MEMORY` parameter work, > > might be the first step? > > > > In particular, this holds for the new versioned-store (but I actually > > believe the is some other internal store with no in-memory > > implementation). -- For `suppress()` it's actually other way around we > > we only have an in-memory implementation. Do you aim to allow custom > > stores for `suppress()`, too? > > > > Btw: Should versioned stores also be covered by the KIP (ie, > > `StoreTypeSpec`)? We did consider to add a new option `VERSIONED` to the > > existing `default.dsl.store` config, but opted out for various reasons. > > > > Last, I am not sure if the new parameter replacing the existing one is > > the best way to go? Did you put the idea to add `CUSTOM` to the existing > > config into rejected alternative. Personally, I would prefer to add > > `CUSTOM` as I would like to optimize to easy of use for the majority of > > users (which don't implement a custom store), but only switch to > > in-memory sometimes. -- As an alternative, you would also just extend > > `dsl.default.store` (it's just a String) and allow to pass in anything. > > If it's matches existing `ROCKS_DB` or `IN_MEMORY` we just process it as > > we do know, and if know we assume it's a fully qualified class name and > > try to instantiate it? -- Given that we plan to keep the store-enum, is > > seems cleaner to keep the existing config and keep both the config and > > enum aligned to each other? > > > > > > It's just preliminary thought. I will need to go back an take a more > > detailed look into the code to grok how the propose `StoreTypeSpec` > > falls into place. Also wondering how it would related to the existing > > `Stores` factory? > > > > -Matthias > > > > > > On 7/21/23 6:45 AM, Colt McNealy wrote: > > > Sophie— > > > > > > Thanks for chiming in here. +1 to the idea of specifying the ordering > > > guarantees that we make in the StorageTypeSpec javadocs. > > > > > > Quick question then. Is the javadoc that says: > > > > > >> Order is not guaranteed as bytes lexicographical ordering might not > > > represent key order. > > > > > > no longer correct, and should say: > > > > > >> Order guarantees depend on the underlying implementation of the > > > ReadOnlyKeyValueStore. For more information, please consult the > > > [StorageTypeSpec javadocs](....) > > > > > > Thanks, > > > Colt McNealy > > > > > > *Founder, LittleHorse.dev* > > > > > > > > > On Thu, Jul 20, 2023 at 9:28 PM Sophie Blee-Goldman < > > ableegold...@gmail.com> > > > wrote: > > > > > >> Hey Almog, first off, thanks for the KIP! I (and others) raised > concerns > > >> over how restrictive the default.dsl.store config would be if not > > >> extendable to custom store types, especially given that this seems to > be > > >> the primary userbase of such a feature. At the time we didn't really > > have > > >> any better ideas for a clean way to achieve that, but what you > proposed > > >> makes a lot of sense to me. Happy to see a good solution to this, and > > >> hopefully others will share my satisfaction :P > > >> > > >> I did have one quick piece of feedback which arose from an unrelated > > >> question posed to the dev mailing list w/ subject line > > >> "ReadOnlyKeyValueStore#range() > > >> Semantics" > > >> <https://lists.apache.org/thread/jbckmth8d3mcgg0rd670cpvsgwzqlwrm>. I > > >> recommend checking out the full thread for context, but it made me > think > > >> about how we can leverage the new StoreTypeSpec concept as an answer > to > > the > > >> long-standing question in Streams: where can we put guarantees of the > > >> public contract for RocksDB (or other store implementations) when all > > the > > >> RocksDB stuff is technically internal. > > >> > > >> Basically, I'm suggesting two things: first, call out in some way > > (perhaps > > >> the StoreTypeSpec javadocs) that each StoreTypeSpec is considered a > > public > > >> contract in itself and should outline any semantic guarantees it does, > > or > > >> does not, make. Second, we should add a note on ordering guarantees in > > the > > >> two OOTB specs: for RocksDB we assert that range queries will honor > > >> serialized byte ordering, whereas the InMemory flavor gives no > ordering > > >> guarantee whatsoever at this time. > > >> > > >> Thoughts? > > >> > > >> -Sophie > > >> > > >> On Thu, Jul 20, 2023 at 4:28 PM Almog Gavra <almog.ga...@gmail.com> > > wrote: > > >> > > >>> Hi All, > > >>> > > >>> I would like to propose a KIP to expand support for default store > types > > >>> (KIP-591) to encompass custom store implementations: > > >>> > > >>> > > >> > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-954%3A+expand+default+DSL+store+configuration+to+custom+types > > >>> > > >>> Looking forward to your feedback! > > >>> > > >>> Cheers, > > >>> Almog > > >>> > > >> > > > > > >
