Thanks for the reply, Sagar, Thanks for bringing up the point about documentation, I do think it would be a great idea for us to add a section to the IQ doc page that's basically a "store extension guide" that gives an overview of how to implement custom queries and custom stores. That would help people see how to go about extending Streams to meet their own needs, and also how to put together a PR to add new queries to Kafka Streams if/when they want to contribute their new queries upstream.
I will mention that when I make my next batch of updates to the KIP (hopefully today). Regarding remote query, the short answer is that, no, this KIP doesn't imclude any new remote query capabilities. I have mulled over remote queries for a while now. On one hand, I would be really cool if Streams provided that functionality natively. On the other hand, it introduces an entirely new client-to-client communication pattern, which doesn't exist anywhere in Apache Kafka today. I'm worried that such an expansion would open Pandora's box in terms of the complexity of configuring Streams, security models, etc. It's possible, if IQ becomes a much more significant part of Streams's capabilities, that the benefits of implementing remote query could one day overcome the costs, but it doesn't seem like that day is today. That's the main reason I've held off from proposing remote query capabilities in the past. Specifically for this KIP, it's just outside the scope; this KIP is really focused on improving the framework for executing local queries. Thanks again! -John On Wed, 2021-11-17 at 22:09 +0530, Sagar wrote: > Thanks John for answering the 2 questions. Pt #1 makes sense to me now. > > Regarding Pt #2, first of all thanks for bringing up KIP-614 :D I did learn > about the interfaces the hard way and probably due to that, the PR really > stretched a lot. Having said that, the point that you mentioned about any > future implementations needing to worry about the base stores, caching and > metered stores, would it make sense to add them explicitly to the KIP and > also to Javadocs if possible? That would guide the future contributors. > WDYT? > > The other question I have is (may be irrelevant) but with these changes, is > there going to be any impact on remote state store querying capabilities? > > Thanks! > Sagar. > > On Tue, Nov 16, 2021 at 4:22 AM John Roesler <vvcep...@apache.org> wrote: > > > Hi Patrick and Sagar, > > > > Thanks for the feedback! I'll just break out the questions > > and address them one at a time. > > > > Patrick 1. > > The default bound that I'm proposing is only to let active > > tasks answer queries (which is also the default with IQ > > today). Therefore, calling getPositionBound() would return a > > PositionBound for which isLatest() is true. > > > > Patrick 2. > > I might have missed something in revision, but I'm not sure > > what you're referring to exactly when you say they are > > different. The IQRequest only has a PositionBound, and the > > IQResponse only has a (concrete) Position, so I think they > > are named accordingly (getPositionBound and getPosition). Am > > I overlooking what you are talking about? > > > > Sagar 1. > > I think you're talking about the KeyValueStore#get(key) > > method? This is a really good question. I went ahead and > > dropped in an addendum to the KeyQuery example to show how > > you would run the query in today's API. Here's a caracature > > of the two APIS: > > > > current: > > KeyValueStore store = kafkaStreams.store( > > "mystore", > > keyValueStore()) > > int value = store.get(key); > > > > proposed: > > int value = kafkaStreams.query( > > "mystore", > > KeyQuery.withKey(key)); > > > > So, today we first get the store interface and then we > > invoke the method, and under the proposal, we would instead > > just ask KafkaStreams to execute the query on the store. In > > addition to all the other stuff I said in the motivation, > > one thing I think is neat about this API is that it means we > > can re-use queries across stores. So, for example, we could > > also use KeyQuery on WindowStores, even though there's no > > common interface between WindowStore and KeyValueStore. > > > > In other words, stores can support any queries that make > > sense and _not_ support any queries that don't make sense. > > This gets into your second question... > > > > Sagar 2. > > Very good question. Your experience with your KIP-614 > > contribution was one of the things that made me want to > > revise IQ to begin with. It seems like there's a really > > stark gap between how straightforward the proposal is to add > > a new store operation, and then how hard it is to actually > > implement a new operation, due to all those intervening > > wrappers. > > > > There are two categories of wrappers to worry about: > > - Facades: These only exist to disallow access to write > > APIs, which are exposed through IQ today but shouldn't be > > called. These are simply unnecessary under IQv2, since we > > only run queries instead of returning the whole store. > > - Store Layers: This is what you provided examples of. We > > have store layers that let us compose features like > > de/serialization and metering, changelogging, caching, etc. > > A nice thing about this design is that we mostly don't have > > to worry at all about those wrapper layers at all. Each of > > these stores would simply delegate any query to lower layers > > unless there is something they need to do. In my POC, I > > simply added a delegating implementation to > > WrappedStateStore, which meant that I didn't need to touch > > most of the wrappers when I added a new query. > > > > Here's what I think future contributors will have to worry > > about: > > 1. The basic query execution in the base byte stores > > (RocksDB and InMemory) > > 2. The Caching stores IF they want the query to be served > > from the cache > > 3. The Metered stores IF some serialization needs to be done > > for the query > > > > And that's it! We should be able to add new queries without > > touching any other store layer besides those, and each one > > of those is involved because it has some specific reason to > > be. > > > > > > Thanks again, Patrick and Sagar! Please let me know if I > > failed to address your questions, or if you have any more. > > > > Thanks, > > -John > > > > On Mon, 2021-11-15 at 22:37 +0530, Sagar wrote: > > > Hi John, > > > > > > Thanks for the great writeup! Couple of things I wanted to bring up(may > > or > > > mayn't be relevant): > > > > > > 1) The sample implementation that you have presented for KeyQuery is very > > > helpful. One thing which may be added to it is how it connects to the > > > KeyValue.get(key) method. That's something that atleast I couldn't > > totally > > > figure out-not sure about others though. I understand that it is out of > > > scope of th KIP to explain for every query that IQ supports but one > > > implementation just to get a sense of how the changes would feel like. > > > 2) The other thing that I wanted to know is that StateStore on it's own > > has > > > a lot of implementations and some of them are wrappers, So at what levels > > > do users need to implement the query methods? Like a MeteredKeyValueStore > > > wraps RocksDbStore and calls it internally through a wrapped call. As per > > > the new changes, how would the scheme of things look like for the same > > > KeyQuery? > > > > > > Thanks! > > > Sagar. > > > > > > > > > On Mon, Nov 15, 2021 at 6:20 PM Patrick Stuedi > > <pstu...@confluent.io.invalid> > > > wrote: > > > > > > > Hi John, > > > > > > > > Thanks for submitting the KIP! One question I have is, assuming one > > > > instantiates InteractiveQueryRequest via withQuery, and then later > > calls > > > > getPositionBound, what will the result be? Also I noticed the Position > > > > returning method is in InteractiveQueryRequest and > > InteractiveQueryResult > > > > is named differently, any particular reason? > > > > > > > > Best, > > > > Patrick > > > > > > > > > > > > On Fri, Nov 12, 2021 at 12:29 AM John Roesler <vvcep...@apache.org> > > wrote: > > > > > > > > > Thanks for taking a look, Sophie! > > > > > > > > > > Ah, that was a revision error. I had initially been planning > > > > > an Optional<Set<Integer>> with Optional.empty() meaning to > > > > > fetch all partitions, but then decided it was needlessly > > > > > complex and changed it to the current proposal with two > > > > > methods: > > > > > > > > > > boolean isAllPartitions(); > > > > > Set<Integer> getPartitions(); (which would throw an > > > > > exception if it's an "all partitions" request). > > > > > > > > > > I've corrected the javadoc and also documented the > > > > > exception. > > > > > > > > > > Thanks! > > > > > -John > > > > > > > > > > On Thu, 2021-11-11 at 15:03 -0800, Sophie Blee-Goldman > > > > > wrote: > > > > > > Thanks John, I've been looking forward to this for a while now. It > > > > > > was pretty horrifying to learn > > > > > > how present-day IQ works (or rather, doesn't work) with custom > > state > > > > > > stores :/ > > > > > > > > > > > > One minor cosmetic point, In the InteractiveQueryRequest class, > > the # > > > > > > getPartitions > > > > > > method has a return type of Set<Integer>, but the javadocs refer to > > > > > Optional. > > > > > > Not > > > > > > sure which is intended for this API, but if is supposed to be the > > > > return > > > > > > type, do you perhaps > > > > > > mean for it to be Optional.ofEmpty() and Optional.of(non-empty > > set) > > > > > > rather than Optional.of(empty set) and Optional.of(non-empty set) ? > > > > > > > > > > > > On Thu, Nov 11, 2021 at 12:03 PM John Roesler <vvcep...@apache.org > > > > > > > > wrote: > > > > > > > > > > > > > Hello again, all, > > > > > > > > > > > > > > Just bumping this discussion on a new, more flexible > > > > > > > Interactive Query API in Kafka Streams. > > > > > > > > > > > > > > If there are no concerns, I'll go ahead and call a vote on > > > > > > > Monday. > > > > > > > > > > > > > > Thanks! > > > > > > > -John > > > > > > > > > > > > > > On Tue, 2021-11-09 at 17:37 -0600, John Roesler wrote: > > > > > > > > Hello all, > > > > > > > > > > > > > > > > I'd like to start the discussion for KIP-796, which proposes > > > > > > > > a revamp of the Interactive Query APIs in Kafka Streams. > > > > > > > > > > > > > > > > The proposal is here: > > > > > > > > https://cwiki.apache.org/confluence/x/34xnCw > > > > > > > > > > > > > > > > I look forward to your feedback! > > > > > > > > > > > > > > > > Thank you, > > > > > > > > -John > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
