Hi Zakelly, Thanks for your reply!
> My advice would be to conceal RedistributionMode/Strategy from the standard user interface, particularly within the helper class 'State'. But I'm OK to keep it in `StateDeclaration` since its interfaces are basically used by the framework. I'm sorry, I didn't mention some of the details/concepts introduced by the Umbrella FLIP and FLIP-409 in this FLIP. This might make it hard to understand the motivation behind RedistributionMode, I'll add more context in FLIP then. Briefly, in V2, we explicitly define the concept of partition. In the case of KeyedPartitionStream, one key corresponds to one partition.For NonKeyedPartitionStream one parallelism/subtask corresponds to one partition. All states are considered to be confined within the partition. On this basis, an obvious question is whether and how the state should be redistribution when the partition changes? So we divide the state into three categories: - Don't need to redistribute states when the partition changes. - Has to decide how to distribute states when the partition changes. - Always has the same state across different partitions. After introducing the concept of partition, the redistribution pattern/mode of state is the more essential difference between states. For this reason, we don't want to emphasize keyed/operator state in the V2 API any more. Keep in mind, partition are first-class citizens. And, even in V1, we have to let the user know that split/union are two different strategies for list state. As for whether or not to expose RedistributionMode to users, I have an open mind. But as I said just now, we still can't avoid this problem in the splitRedistributionListState and unionRedistributionListState. IMO, it's better to explain it in the API level instead of avoiding it. WDTY? Best regards, Weijie weijie guo <guoweijieres...@gmail.com> 于2024年3月7日周四 16:39写道： > Hi Gyula, > > > Thanks for your reply! > > > Let me answer these questions: > > > > What is the semantics of the usesStates method? When is it called? Can > the used state change dynamically at runtime? Can the logic depend on > something computed in open(..) for example? > > > > useStates is used to predefine all the states that the process function needs > to access. In other words, we want to avoid declaring the state dynamically > at runtime and this allows the SQL planner and JM to optimize the job better. > As a result, this logic must be fully available at compile time (when the > JobGraph is generated), so it can't rely on computations that are executed > after deploy to TM. > > > > > Currently state access is pretty dynamic in Flink and I would assume many > jobs create states on the fly based on some required logic. Are we planning > to address these use-cases? > > > It depends on what type of context we need. If the type and number of states > depend on runtime context, that's something we want to avoid. If it only > depended on information available at compile time, I think we could support > it. > > > > > Are we planning to support deleting/dropping states that are not required > anymore? > > > > We really don't want the user to be able to dynamically declare/delete a > state at runtime, but if you just want to clear/clean the value of state, the > new API works the same as the old API. > > > > I think if a state is not declared or otherwise cannot be accessed, an > exceptions must be thrown. We cannot confuse empty value with something > inaccessible. > > > After thinking about it a bit more, I think you have a point! > It's important to make a clear distinction between an empty state and illegal > access, especially since flink currently discourage setting a non-null > default value for the state. > I will modify the proposal as you suggested then :) > > > > The RedistributionMode enum sounds a bit strange to me, as it doesn't > actually specify a mode of redistribution. It feels more like a flag. Can > we simply have an Optional<RedistributionStrategy> instead? > > > We actually define three types RedistributionMode instead of two because > we don't want to think of IDENTICAL as a redistribution strategy, it's just > an invariant: the State of that type is always the same across partitions. > If it only has None and REDISTRIBUTABLE, I think your proposal is > feasible then. But we don't want to confuse these three semantics/modes. > > > > BroadcastStates are currently very limited by only Map-like states, and > the new interface also enforces that. Can we remove this limitation? If > not, should broadcastState declaration extend mapstate declaration? > > > > Personally, I don't want to make this restriction. This is also why the > method in StateManager to get BroadcastState has the parameter of > BroadcastStateDeclaration instead of MapStateDeclaration. In the future, if > the state backend supports other types of broadcast state, we can add a > corresponding method to the States utility class to get the > BroadcastSateDeclaration. > > > > Best regards, > > Weijie > > > Hangxiang Yu <master...@gmail.com> 于2024年3月7日周四 11:55写道： > >> Hi, Weijie. >> Thanks for your proposal. >> I'd like to start the discussion with some questions: >> 1. We have also discussed in FLIP-359/FLINK-32658 about limiting the user >> operation to avoid creating state when processElement. Could current >> interfaces also help this? >> >> 2. Could you provide more examples about how useStates() works ? Since >> some >> operations may change their used states at runtime, the value this method >> returns will be modified at runtime, right ? >> If so, I'm thinking if we could get some deterministic State Declaration >> Set before running which could help a lot for some state operations e.g. >> pre-check schema compatibility, queryable schema. >> >> 3. IIUC, RedistributionMode/Strategy should not be used by users, right ? >> If so, I'm +1 to move them to inner interfaces which seems a bit confusing >> to users. >> >> On Thu, Mar 7, 2024 at 11:39 AM Zakelly Lan <zakelly....@gmail.com> >> wrote: >> >> > Hi Weijie, >> > >> > Thanks for proposing this! >> > >> > Unifying and optimizing state definitions is a very good thing. I like >> the >> > idea of 'definition goes before using', so overall +1 for this proposal. >> > >> > However, I think the current definition is somewhat unclear. From a >> user's >> > point of view, I believe that state can be characterized along two >> > relatively independent axes: the scenario (keyed, non-keyed, or >> broadcast) >> > and the data structure (single value, list, map). I recommend that we >> fully >> > decouple these aspects, rather than linking the nature of the >> definition to >> > specific assumptions, such as equating broadcast states with maps, or >> > considering list states could be non-keyed. >> > Furthermore, the concept of 'Redistribution' may impose a cognitive >> burden >> > on general users. My advice would be to conceal >> RedistributionMode/Strategy >> > from the standard user interface, particularly within the helper class >> > 'State'. But I'm OK to keep it in `StateDeclaration` since its >> interfaces >> > are basically used by the framework. My preferred syntax would be: >> > ``` >> > StateDeclaration a = State.declare(name).keyed().listState(type); >> > StateDeclaration b = State.declare(name).broadcast().mapState(typeK, >> > typeV); >> > StateDeclaration c = State.declare(name).keyed().aggregatingState(type, >> > function); >> > ``` >> > WDYT? >> > >> > >> > Best, >> > Zakelly >> > >> > On Wed, Mar 6, 2024 at 11:04 PM Gyula Fóra <gyula.f...@gmail.com> >> wrote: >> > >> > > Hi Weijie! >> > > >> > > Thank you for the proposal. >> > > >> > > I have some initial questions to start the discussion: >> > > >> > > 1. What is the semantics of the usesStates method? When is it called? >> Can >> > > the used state change dynamically at runtime? Can the logic depend on >> > > something computed in open(..) for example? >> > > >> > > Currently state access is pretty dynamic in Flink and I would assume >> many >> > > jobs create states on the fly based on some required logic. Are we >> > planning >> > > to address these use-cases? >> > > >> > > Are we planning to support deleting/dropping states that are not >> required >> > > anymore? >> > > >> > > 2. Get state now returns an optional, but you mention that: >> > > " If you want to get a state that is not declared or has no access, >> > > Option#empty is returned." >> > > >> > > I think if a state is not declared or otherwise cannot be accessed, an >> > > exceptions must be thrown. We cannot confuse empty value with >> something >> > > inaccessible. >> > > >> > > 3. The RedistributionMode enum sounds a bit strange to me, as it >> doesn't >> > > actually specify a mode of redistribution. It feels more like a flag. >> Can >> > > we simply have an Optional<RedistributionStrategy> instead? >> > > >> > > 4. BroadcastStates are currently very limited by only Map-like states, >> > and >> > > the new interface also enforces that. >> > > Can we remove this limitation? If not, should broadcastState >> declaration >> > > extend mapstate declaration? >> > > >> > > Cheers, >> > > Gyula >> > > >> > > Cheers >> > > Gyuka >> > > >> > > On Wed, Mar 6, 2024 at 11:18 AM weijie guo <guoweijieres...@gmail.com >> > >> > > wrote: >> > > >> > > > Hi devs, >> > > > >> > > > I'd like to start a discussion about FLIP-433: State Access on >> > > > DataStream API V2 >> > > > [1]. This is the third sub-FLIP of DataStream API V2. >> > > > >> > > > >> > > > After FLIP-410 [2], we can already write a simple stateless job >> using >> > the >> > > > DataStream V2 API. But as we all know, stateful computing is >> Flink's >> > > trump >> > > > card. In this FLIP, we will discuss how to declare and access state >> on >> > > > DataStream API V2 and we manage to avoid some of the shortcomings >> of V1 >> > > in >> > > > this regard. >> > > > >> > > > You can find more details in this FLIP. Its relationship with other >> > > > sub-FLIPs can be found in the umbrella FLIP >> > > > [3]. Looking forward to hearing from you, thanks! >> > > > >> > > > >> > > > Best regards, >> > > > >> > > > Weijie >> > > > >> > > > >> > > > [1] >> > > > >> > > > >> > > >> > >> https://cwiki.apache.org/confluence/display/FLINK/FLIP-433%3A+State+Access+on+DataStream+API+V2 >> > > > >> > > > [2] >> > > > >> > > > >> > > >> > >> https://cwiki.apache.org/confluence/display/FLINK/FLIP-410%3A++Config%2C+Context+and+Processing+Timer+Service+of+DataStream+API+V2 >> > > > >> > > > [3] >> > > > >> > > > >> > > >> > >> https://cwiki.apache.org/confluence/display/FLINK/FLIP-408%3A+%5BUmbrella%5D+Introduce+DataStream+API+V2 >> > > > >> > > >> > >> >> >> -- >> Best, >> Hangxiang. >> >
