Hi Weijie, Thanks for your answer! Well I get your point. Since partitions are first-class citizens, and redistribution means how states migrate when partitions change, I'd be fine with deemphasizing the concept of keyed/operator state if we highlight the definition of partition in the document. Keeping `RedistributionMode` under `StateDeclaration` is also fine with me, as I guess it is only for internal usage. But still, from a user's point of view, state can be characterized along two relatively independent dimensions, how states redistribute and the data structure. Thus I still suggest a chained-like configuration API that configures one aspect on each call, such as: ``` # Keyed stream, no redistribution mode specified, the state will go with partition (no redistribution). ---- Keyed state StateDeclaration a = States.declare(name).listState(type);
# Keyed stream, redistribution strategy specified, the state follows the specified redistribute strategy. ---- Operator state StateDeclaration b = States.declare(name).listState(type).redistributeBy(strategy); # Non-keyed stream, redistribution strategy *must be* specified. StateDeclaration c = States.declare(name).listState(type).redistributeBy(strategy); # Broadcast stream and state StateDeclaration d = States.declare(name).mapState(typeK, typeV).broadcast(); ``` It can drive users to think about redistribution issues when needed. And it also provides more flexibility to add more combinations such as broadcasting list state, or chain more configurable aspects such as adding `withTtl()` in future. WDYT? Best, Zakelly On Thu, Mar 7, 2024 at 6:04 PM weijie guo <guoweijieres...@gmail.com> wrote: > Hi Jinzhong, > > Thanks for the reply! > > > Overall, I think that the “Eager State Declaration” is a good proposal, > which can enhance Flink's state management capabilities and provide > possibilities for subsequent state optimizations. > > It's nice to see that people who are familiar with the state stuff like > this proposal. :) > > > When the user attempts to access an undeclared state at runtime, it is > more reasonable to throw an exception rather than returning Option#empty, > as Gyula mentioned above. > > Yes, I agree that this is better then a confused empty, and I have modified > the corresponding part of this FLIP. > > > In addition, I'm not quite sure whether all of the existing usage in > which states are registered at runtime dynamically can be migrated to the > "Eager State Declaration" style with minimal cost? > > I think for most user functions, this is fairly straightforward to migrate. > But states whose declarations depend on runtime information(e.g. > RuntimeContext) are, in principle, not supported in the new API. Anyway, > the old and new apis are completely incompatible, so rewriting jobs is > inevitable. User can think about how to write a good process function that > conforms to the eager declaration style. > > > For state TTL, should StateDeclaration also provide interfaces for users > to declare state ttl? > > Of course, We can and we need to provide this one. But whether or not it's > in this FLIP isn't very important for me, because we're mainly talking > about the general principles and ways of declaring and accessing state in > this FLIP. I promise we won't leave it out in the end D). > > > > Best regards, > > Weijie > > > Jinzhong Li <lijinzhong2...@gmail.com> 于2024年3月7日周四 17:34写道： > > > Hi Weijie, > > > > Thanks for driving this! > > > > 1. Overall, I think that the “Eager State Declaration” is a good > proposal, > > which can enhance Flink's state management capabilities and provide > > possibilities for subsequent state optimizations. > > > > 2. When the user attempts to access an undeclared state at runtime, it is > > more reasonable to throw an exception rather than returning Option#empty, > > as Gyula mentioned above. > > In addition, I'm not quite sure whether all of the existing usage in > which > > states are registered at runtime dynamically can be migrated to the > "Eager > > State Declaration" style with minimal cost? > > > > 3. For state TTL, should StateDeclaration also provide interfaces for > users > > to declare state ttl? > > > > Best, > > Jinzhong Li > > > > > > On Thu, Mar 7, 2024 at 5:08 PM weijie guo <guoweijieres...@gmail.com> > > wrote: > > > > > Hi Hangxiang, > > > > > > Thanks for your reply! > > > > > > > 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? > > > > > > I think so. It is illegal to create state at runtime in our proposal. > > > > > > > > > > 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? > > > > > > > > > No, Introducing and declaring new state > > > at runtime is something we want to explicitly disallow. You can simply > > > assume that useState is only called when the JobGraph is generated, > > > and any future changes to it are invalid and illegal. > > > > > > > > > > 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. > > > > > > > > > As for this question, I think my answer to Zakelly should be helpful. > > > > > > > > > > > > Best regards, > > > > > > Weijie > > > > > > > > > weijie guo <guoweijieres...@gmail.com> 于2024年3月7日周四 16:58写道： > > > > > > > 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. > > > >>> > > > >> > > > > > >
