Hi Luke, It’s not my KIP, but my two cents is that users should not run the reset tool while the application is paused.
The reset tool should only be run while the whole app is shut down because it messes with a lot of internal state bits without synchronization. Leaving the app running (even while pausing processing) will result in the app being in an undefined state, as the members and the tool will be simultaneously trying to set the committed offsets to different values, etc. Jim, can you also make it a point to document this? As Luke points out, it might be a natural thing to want to do. Thanks, John On Wed, May 11, 2022, at 02:19, Luke Chen wrote: > Hi Jim, > > Thanks for the KIP. Overall LGTM! > > One late question: > Could we run the stream resetter tool (i.e. > kafka-streams-application-reset.sh) during pause state? > I can imagine there's a use case that after pausing for a while, user just > want to continue with the latest offset, and skipping the intermediate > records. > > Thank you. > Luke > > On Wed, May 11, 2022 at 10:12 AM Jim Hughes <jhug...@confluent.io.invalid> > wrote: > >> Hi Matthias, >> >> I like it. I've updated the KIP to reflect that detail; I put the details >> in the docs for pause. >> >> Cheers, >> >> Jim >> >> On Tue, May 10, 2022 at 7:51 PM Matthias J. Sax <mj...@apache.org> wrote: >> >> > Thanks for the KIP. Overall LGTM. >> > >> > Can we clarify one question: would it be allowed to call `pause()` >> > before calling `start()`? I don't see any reason why we would need to >> > disallow it? >> > >> > It could be helpful to start a KafkaStreams client in paused state -- >> > otherwise there is a race between calling `start()` and calling >> `pause()`. >> > >> > If we allow it, we should clearly document it. >> > >> > >> > -Matthias >> > >> > On 5/10/22 12:04 PM, Jim Hughes wrote: >> > > Hi Bill, all, >> > > >> > > Thank you. I've updated the KIP to reflect pausing standby tasks as >> > well. >> > > I think all the outstanding points have been addressed and I'm going to >> > > start the vote thread! >> > > >> > > Cheers, >> > > >> > > Jim >> > > >> > > >> > > >> > > On Tue, May 10, 2022 at 2:43 PM Bill Bejeck <bbej...@gmail.com> wrote: >> > > >> > >> Hi Jim, >> > >> >> > >> After reading the comments on the KIP, I agree that it makes sense to >> > pause >> > >> all activities and any changes can be made later on. >> > >> >> > >> Thanks, >> > >> Bill >> > >> >> > >> On Tue, May 10, 2022 at 4:03 AM Bruno Cadonna <cado...@apache.org> >> > wrote: >> > >> >> > >>> Hi Jim, >> > >>> >> > >>> Thanks for the KIP! >> > >>> >> > >>> I am fine with the KIP in general. >> > >>> >> > >>> However, I am with Sophie and John to also pause the standbys for the >> > >>> reasons they brought up. Is there a specific reason you want to keep >> > >>> standbys going? It feels like premature optimization to me. We can >> > still >> > >>> add keeping standby running in a follow up if needed. >> > >>> >> > >>> Best, >> > >>> Bruno >> > >>> >> > >>> On 10.05.22 05:15, Sophie Blee-Goldman wrote: >> > >>>> Thanks Jim, just one note/question on the standby tasks: >> > >>>> >> > >>>> At the minute, my moderately held position is that standby tasks >> ought >> > >> to >> > >>>>> continue reading and remain caught up. If standby tasks would run >> > out >> > >>> of >> > >>>>> space, there are probably bigger problems. >> > >>>> >> > >>>> >> > >>>> For a single node application, or when the #pause API is invoked on >> > all >> > >>>> instances, >> > >>>> then there won't be any further active processing and thus nothing >> to >> > >>> keep >> > >>>> up with, >> > >>>> right? So for that case, it's just a matter of whether any standbys >> > >> that >> > >>>> are lagging >> > >>>> will have the chance to catch up to the (paused) active task state >> > >> before >> > >>>> they stop >> > >>>> as well, in which case having them continue feels fine to me. >> However >> > >>> this >> > >>>> is a >> > >>>> relatively trivial benefit and I would only consider it as a >> deciding >> > >>>> factor when all >> > >>>> things are equal otherwise. >> > >>>> >> > >>>> My concern is the more interesting case: when this feature is used >> to >> > >>> pause >> > >>>> only >> > >>>> one nodes, or some subset of the overall application. In this case, >> > >> yes, >> > >>>> the standby >> > >>>> tasks will indeed fall out of sync. But the only reason I can >> imagine >> > >>>> someone using >> > >>>> the pause feature in such a way is because there is something going >> > >>> wrong, >> > >>>> or about >> > >>>> to go wrong, on that particular node. For example as mentioned >> above, >> > >> if >> > >>>> the user >> > >>>> wants to cut down on costs without stopping everything, or if the >> node >> > >> is >> > >>>> about to >> > >>>> run out of disk or needs to be debugged or so on. And in this case, >> > >>>> continuing to >> > >>>> process the standby tasks while other instances continue to run >> would >> > >>>> pretty much >> > >>>> defeat the purpose of pausing it entirely, and might have unpleasant >> > >>>> consequences >> > >>>> for the unsuspecting developer. >> > >>>> >> > >>>> All that said, I don't want to block this KIP so if you have strong >> > >>>> feelings about the >> > >>>> standby behavior I'm happy to back down. I'm only pushing back now >> > >>> because >> > >>>> it >> > >>>> felt like there wasn't any particular motivation for the standbys to >> > >>>> continue processing >> > >>>> or not, and I figured I'd try to fill in this gap with my thoughts >> on >> > >> the >> > >>>> matter :) >> > >>>> Either way we should just make sure that this behavior is documented >> > >>>> clearly, >> > >>>> since it may be surprising if we decide to only pause active >> > processing >> > >>>> (another option >> > >>>> is to rename the method something like #pauseProcessing or >> > >>>> #pauseActiveProcessing >> > >>>> so that it's hard to miss). >> > >>>> >> > >>>> Thanks! Sorry for the lengthy response, but hopefully we won't need >> to >> > >>>> debate this any >> > >>>> further. Beyond this I'm satisfied with the latest proposal >> > >>>> >> > >>>> On Mon, May 9, 2022 at 5:16 PM John Roesler <vvcep...@apache.org> >> > >> wrote: >> > >>>> >> > >>>>> Thanks for the updates, Jim! >> > >>>>> >> > >>>>> After this discussion and your updates, this KIP looks good to me. >> > >>>>> >> > >>>>> Thanks, >> > >>>>> John >> > >>>>> >> > >>>>> On Mon, May 9, 2022, at 17:52, Jim Hughes wrote: >> > >>>>>> Hi Sophie, all, >> > >>>>>> >> > >>>>>> I've updated the KIP with feedback from the discussion so far: >> > >>>>>> >> > >>>>> >> > >>> >> > >> >> > >> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=211882832 >> > >>>>>> >> > >>>>>> As a terse summary of my current position: >> > >>>>>> Pausing will only stop processing and punctuation (respecting >> > modular >> > >>>>>> topologies). >> > >>>>>> Paused topologies will still a) consume from input topics, b) call >> > >> the >> > >>>>>> usual commit pathways (commits will happen basically as they would >> > >>> have), >> > >>>>>> and c) standBy tasks will still be processed. >> > >>>>>> >> > >>>>>> Shout if the KIP or those details still need some TLC. Responding >> > to >> > >>>>>> Sophie inline below. >> > >>>>>> >> > >>>>>> >> > >>>>>> On Mon, May 9, 2022 at 6:06 PM Sophie Blee-Goldman >> > >>>>>> <sop...@confluent.io.invalid> wrote: >> > >>>>>> >> > >>>>>>> Don't worry, I'm going to be adding the APIs for topology-level >> > >>> pausing >> > >>>>> as >> > >>>>>>> part of the modular topologies KIP, >> > >>>>>>> so we don't need to worry about that for now. That said, I don't >> > >> think >> > >>>>> we >> > >>>>>>> should brush it off entirely and design >> > >>>>>>> this feature in a way that's going to be incompatible or hugely >> > >> raise >> > >>>>> the >> > >>>>>>> LOE on bringing the (mostly already >> > >>>>>>> implemented) modular topologies feature into the public API, just >> > >>>>>>> because it "won the race to write a KIP" :) >> > >>>>>>> >> > >>>>>> >> > >>>>>> Yes, I'm hoping that this is all compatible with modular >> > >> topologies. I >> > >>>>>> haven't seen anything so far which seems to be a problem; this KIP >> > is >> > >>>>> just >> > >>>>>> in a weird state to discuss details of acting on modular >> > >> topologies.:) >> > >>>>>> >> > >>>>>> >> > >>>>>>> I may be biased (ok, I definitely am), but I'm not in favor of >> > >> adding >> > >>>>> this >> > >>>>>>> as a state regardless of the modular topologies. >> > >>>>>>> First of all any change to the KafkaStreams state machine is a >> > >>> breaking >> > >>>>>>> change, no? So we would have to wait until >> > >>>>>>> the next major release which seems like an unnecessary thing to >> > >> block >> > >>>>> on. >> > >>>>>>> (Whether to add this as a state to the >> > >>>>>>> StreamThread's FSM is an implementation detail). >> > >>>>>>> >> > >>>>>> >> > >>>>>> +1. I am sold on skipping out on new states. I had that as a >> > >> rejected >> > >>>>>> alternative in the KIP and have added a few more words to that >> bit. >> > >>>>>> >> > >>>>>> >> > >>>>>>> Also, the semantics of using an `isPaused` method to distinguish >> a >> > >>>>> paused >> > >>>>>>> instance (or topology) make more sense >> > >>>>>>> to me -- this is a user-specified status, whereas the >> KafkaStreams >> > >>>>> state is >> > >>>>>>> intended to relay the status of the system >> > >>>>>>> itself. For example, if we are going to continue to poll during >> > >> pause, >> > >>>>> then >> > >>>>>>> shouldn't the client transition to REBALANCING? >> > >>>>>>> I believe it makes sense to still allow distinguishing these >> states >> > >>>>> while a >> > >>>>>>> client is paused, whereas making PAUSED its >> > >>>>>>> own state means you can't tell when the client is rebalancing vs >> > >>>>> running, >> > >>>>>>> or whether it is paused or dead: presumably >> > >>>>>>> the NOT_RUNNING/ERROR state would trump the PAUSED state, which >> > >> means >> > >>>>> you >> > >>>>>>> would not be able to rely on >> > >>>>>>> checking the state to see if you had called PAUSED on that >> > instance. >> > >>>>>>> Obviously you can work around this by just >> > >>>>>>> maintaining a flag in the usercode, but all this feels very >> > >> unnatural >> > >>>>> to me >> > >>>>>>> vs just checking the `#isPaused` API. >> > >>>>>>> >> > >>>>>>> On that note, I had one question -- at what point would the >> > >>> `#isPaused` >> > >>>>>>> check return true? Would it do so immediately >> > >>>>>>> after pausing the instance, or only once it has finished >> committing >> > >>>>> offsets >> > >>>>>>> and stopped returning records? >> > >>>>>>> >> > >>>>>> >> > >>>>>> Immediately, `#isPaused` tells you about metadata. >> > >>>>>> >> > >>>>>> >> > >>>>>>> Finally, on the note of punctuators I think it would make most >> > sense >> > >>> to >> > >>>>>>> either pause these as well or else add this an >> > >>>>>>> an explicit option for the user. If this feature is used to, for >> > >>>>> example, >> > >>>>>>> help save on processing costs while an app is >> > >>>>>>> not in use, then it would probably be surprising and perhaps >> > >> alarming >> > >>> to >> > >>>>>>> see certain kinds of processing still continue. >> > >>>>>>> >> > >>>>>> >> > >>>>>> From other parts of the discussion, I'm sold on pausing >> > punctuation. >> > >>>>>> >> > >>>>>> >> > >>>>>>> The question of whether to continue fetching for standby tasks is >> > >>> maybe >> > >>>>> a >> > >>>>>>> bit more debatable, as it would certainly be >> > >>>>>>> nice to find your clients all caught up when you go to resume the >> > >>>>> instance >> > >>>>>>> again, but I would still strongly suggest >> > >>>>>>> pausing these as well. To use a similar example, imagine if you >> > >> paused >> > >>>>> an >> > >>>>>>> app because it was about to run out of >> > >>>>>>> disk. If the standbys kept processing and filled up the remaining >> > >>> space, >> > >>>>>>> you'd probably feel a bit betrayed by this API. >> > >>>>>>> >> > >>>>>>> WDYT? >> > >>>>>>> >> > >>>>>> >> > >>>>>> At the minute, my moderately held position is that standby tasks >> > >> ought >> > >>> to >> > >>>>>> continue reading and remain caught up. If standby tasks would run >> > >> out >> > >>> of >> > >>>>>> space, there are probably bigger problems. >> > >>>>>> >> > >>>>>> If later it is desirable to manage punctuation or standby tasks, >> > then >> > >>> it >> > >>>>>> should be easy for future folks to modify things. >> > >>>>>> >> > >>>>>> Overall, I'd frame this KIP as "pause processing resulting in >> > >> outputs". >> > >>>>>> >> > >>>>>> Cheers, >> > >>>>>> >> > >>>>>> Jim >> > >>>>>> >> > >>>>>> >> > >>>>>> >> > >>>>>>> On Mon, May 9, 2022 at 10:33 AM Guozhang Wang < >> wangg...@gmail.com> >> > >>>>> wrote: >> > >>>>>>> >> > >>>>>>>> I think for named topology we can leave the scope of this KIP as >> > >> "all >> > >>>>> or >> > >>>>>>>> nothing", i.e. when you pause an instance you pause all of its >> > >>>>>>> topologies. >> > >>>>>>>> I raised this question in my previous email just trying to >> clarify >> > >> if >> > >>>>>>> this >> > >>>>>>>> is what you have in mind. We can leave the question of finer >> > >>>>> controlled >> > >>>>>>>> pausing behavior for later when we have named topology being >> > >> exposed >> > >>>>> via >> > >>>>>>>> another KIP. >> > >>>>>>>> >> > >>>>>>>> >> > >>>>>>>> Guozhang >> > >>>>>>>> >> > >>>>>>>> On Mon, May 9, 2022 at 7:50 AM John Roesler < >> vvcep...@apache.org> >> > >>>>> wrote: >> > >>>>>>>> >> > >>>>>>>>> Hi Jim, >> > >>>>>>>>> >> > >>>>>>>>> Thanks for the replies. This all sounds good to me. Just two >> > >> further >> > >>>>>>>>> comments: >> > >>>>>>>>> >> > >>>>>>>>> 3. It seems like you should aim for the simplest semantics. If >> > the >> > >>>>>>> intent >> > >>>>>>>>> is to “pause” the instance, then you’d better pause the whole >> > >>>>> instance. >> > >>>>>>>> If >> > >>>>>>>>> you leave punctuations and standbys running, I expect we’d see >> > bug >> > >>>>>>>> reports >> > >>>>>>>>> come in that the instance isn’t really paused. >> > >>>>>>>>> >> > >>>>>>>>> 5. Since you won the race to write a KIP, I don’t think it >> makes >> > >> too >> > >>>>>>> much >> > >>>>>>>>> sense to worry too much about modular topologies. When they >> > >> propose >> > >>>>>>> their >> > >>>>>>>>> KIP, they will have to specify a lot of state management >> > behavior, >> > >>>>> and >> > >>>>>>>>> pause/resume will have to be part of it. If they have some >> > concern >> > >>>>>>> about >> > >>>>>>>>> your KIP, they’ll chime in. It doesn’t make sense for you to >> try >> > >> and >> > >>>>>>>> guess >> > >>>>>>>>> what that proposal will look like. >> > >>>>>>>>> >> > >>>>>>>>> To be honest, you’re proposing a KafkaStreams runtime-level >> > >>>>>>> pause/resume >> > >>>>>>>>> function, not a topology-level one anyway, so it seems pretty >> > >> clear >> > >>>>>>> that >> > >>>>>>>> it >> > >>>>>>>>> would pause the whole runtime (of a single instance) regardless >> > of >> > >>>>> any >> > >>>>>>>>> modular topologies. If the intent is to pause individual >> > >> topologies >> > >>>>> in >> > >>>>>>>> the >> > >>>>>>>>> future, you’d need a different API anyway. >> > >>>>>>>>> >> > >>>>>>>>> Thanks! >> > >>>>>>>>> -John >> > >>>>>>>>> >> > >>>>>>>>> On Mon, May 9, 2022, at 08:10, Jim Hughes wrote: >> > >>>>>>>>>> Hi John, >> > >>>>>>>>>> >> > >>>>>>>>>> Long emails are great; responding inline! >> > >>>>>>>>>> >> > >>>>>>>>>> On Sat, May 7, 2022 at 4:54 PM John Roesler < >> > vvcep...@apache.org >> > >>> >> > >>>>>>>> wrote: >> > >>>>>>>>>> >> > >>>>>>>>>>> Thanks for the KIP, Jim! >> > >>>>>>>>>>> >> > >>>>>>>>>>> This conversation seems to highlight that the KIP needs to >> > >>>>> specify >> > >>>>>>>>>>> some of its behavior as well as its APIs, where the behavior >> is >> > >>>>>>>>>>> observable and significant to users. >> > >>>>>>>>>>> >> > >>>>>>>>>>> For example: >> > >>>>>>>>>>> >> > >>>>>>>>>>> 1. Do you plan to have a guarantee that immediately after >> > >>>>>>>>>>> calling KafkaStreams.pause(), users should observe that the >> > >>>>> instance >> > >>>>>>>>>>> stops processing new records? Or should they expect that the >> > >>>>> threads >> > >>>>>>>>>>> will continue to process some records and pause >> asynchronously >> > >>>>>>>>>>> (you already answered this in the thread earlier)? >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> I'm happy to build up to a guarantee of sorts. My current >> idea >> > >> is >> > >>>>>>> that >> > >>>>>>>>>> pause() does not do anything "exceptional" to get control back >> > >>>>> from a >> > >>>>>>>>>> running topology. A currently running topology would get to >> > >>>>> complete >> > >>>>>>>> its >> > >>>>>>>>>> loop. >> > >>>>>>>>>> >> > >>>>>>>>>> Separately, I'm still piecing together how commits work. By >> > some >> > >>>>>>>>>> mechanism, after a pause, I do agree that the topology needs >> to >> > >>>>>>> commit >> > >>>>>>>>> its >> > >>>>>>>>>> work in some manner. >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> 2. Will the threads continue to poll new records until they >> > >>>>>>> naturally >> > >>>>>>>>> fill >> > >>>>>>>>>>> up the task buffers, or will they immediately pause their >> > >>>>> Consumers >> > >>>>>>>>>>> as well? >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> Presently, I'm suggesting that consumers would fill up their >> > >>>>> buffers. >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> 3. Will threads continue to call (system time) punctuators, >> or >> > >>>>> would >> > >>>>>>>>>>> punctuations also be paused? >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> In my first pass at thinking through this, I left the >> > punctuators >> > >>>>>>>>> running. >> > >>>>>>>>>> To be honest, I'm not sure what they do, so my approach is >> > either >> > >>>>>>> lucky >> > >>>>>>>>> and >> > >>>>>>>>>> correct or it could be Very Clearly Wrong.;) >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> I realize that some of those questions simply may not have >> > >>>>> occurred >> > >>>>>>> to >> > >>>>>>>>>>> you, so this is not a criticism for leaving them off; I'm >> just >> > >>>>>>>> pointing >> > >>>>>>>>> out >> > >>>>>>>>>>> that although we don't tend to mention implementation details >> > in >> > >>>>>>> KIPs, >> > >>>>>>>>>>> we also can't be too high level, since there are a lot of >> > >>>>>>> operational >> > >>>>>>>>>>> details that users rely on to achieve various behaviors in >> > >>>>> Streams. >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> Ayup, I will add some details as we iron out the guarantees, >> > >>>>>>>>> implementation >> > >>>>>>>>>> details that are at the API level. This one is tough since >> > >>>>> internal >> > >>>>>>>>>> features like NamedTopologies are part of the discussion. >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> A couple more comments: >> > >>>>>>>>>>> >> > >>>>>>>>>>> 4. +1 to what Guozhang said. It seems like we should we also >> do >> > >> a >> > >>>>>>>> commit >> > >>>>>>>>>>> before entering the paused state. That way, any open >> > >> transactions >> > >>>>>>>> would >> > >>>>>>>>>>> be closed and not have to worry about timing out. Even under >> > >>>>> ALOS, >> > >>>>>>> it >> > >>>>>>>>>>> seems best to go ahead and complete the processing of >> in-flight >> > >>>>>>>> records >> > >>>>>>>>>>> by committing. That way, if anything happens to die while >> it's >> > >>>>>>> paused, >> > >>>>>>>>>>> existing >> > >>>>>>>>>>> work won't have to be repeated. Plus, if there are any >> > >> processors >> > >>>>>>> with >> > >>>>>>>>> side >> > >>>>>>>>>>> effects, users won't have to tolerate weird edge cases where >> a >> > >>>>> pause >> > >>>>>>>>> occurs >> > >>>>>>>>>>> after a processor sees a record, but before the result is >> sent >> > >> to >> > >>>>>>> its >> > >>>>>>>>>>> outputs. >> > >>>>>>>>>>> >> > >>>>>>>>>>> 5. I noticed that you proposed not to add a PAUSED state, >> but I >> > >>>>>>> didn't >> > >>>>>>>>>>> follow >> > >>>>>>>>>>> the rationale. Adding a state seems beneficial for a number >> of >> > >>>>>>>> reasons: >> > >>>>>>>>>>> StreamThreads already use the thread state to determine >> whether >> > >>>>> to >> > >>>>>>>>> process >> > >>>>>>>>>>> or not, so avoiding a new State would just mean adding a >> > >> separate >> > >>>>>>> flag >> > >>>>>>>>> to >> > >>>>>>>>>>> track >> > >>>>>>>>>>> and then checking your new flag in addition to the State in >> the >> > >>>>>>>> thread. >> > >>>>>>>>>>> Also, >> > >>>>>>>>>>> operating Streams applications is a non-trivial task, and >> users >> > >>>>> rely >> > >>>>>>>> on >> > >>>>>>>>>>> the State >> > >>>>>>>>>>> (and transitions) to understand Streams's behavior. Adding a >> > >>>>> PAUSED >> > >>>>>>>>> state >> > >>>>>>>>>>> is an elegant way to communicate to operators what is >> happening >> > >>>>> with >> > >>>>>>>> the >> > >>>>>>>>>>> application. Note that the person digging though logs and >> > >>>>> metrics, >> > >>>>>>>>> trying >> > >>>>>>>>>>> to understand why the application isn't doing anything is >> > >>>>> probably >> > >>>>>>> not >> > >>>>>>>>>>> going >> > >>>>>>>>>>> to be the same person who is calling pause() and resume(). >> > Also, >> > >>>>> if >> > >>>>>>>> you >> > >>>>>>>>> add >> > >>>>>>>>>>> a state, you don't need `isPaused()`. >> > >>>>>>>>>>> >> > >>>>>>>>>>> 5b. If you buy the arguments to go ahead and commit as well >> as >> > >>>>> the >> > >>>>>>>>>>> argument to add a State, then I'd also suggest to follow the >> > >>>>>>> existing >> > >>>>>>>>>>> patterns >> > >>>>>>>>>>> for the shutdown states by also adding PAUSING. That >> > >>>>>>>>>>> way, you'll also expose a way to understand that Streams >> > >> received >> > >>>>>>> the >> > >>>>>>>>>>> signal >> > >>>>>>>>>>> to pause, and that it's still processing and committing some >> > >>>>> records >> > >>>>>>>> in >> > >>>>>>>>>>> preparation to enter a PAUSED state. I'm not sure if a >> RESUMING >> > >>>>>>> state >> > >>>>>>>>> would >> > >>>>>>>>>>> also make sense. >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> I hit a tricky bit when thinking through having a PAUSED >> > >>>>> state... If >> > >>>>>>>> one >> > >>>>>>>>>> is using Named Topologies, and some of them are paused, what >> > >>>>> state is >> > >>>>>>>> the >> > >>>>>>>>>> Streams instance in? If we can agree on that, things may >> become >> > >>>>>>>>> clear.... >> > >>>>>>>>>> I can see two quick ideas: >> > >>>>>>>>>> >> > >>>>>>>>>> 1. The state is RUNNING and NamedTopologies have some other >> way >> > >>>>> to >> > >>>>>>>>>> indicate state. >> > >>>>>>>>>> >> > >>>>>>>>>> 2. The state is something messy like PARTIALLY_PAUSED to >> > reflect >> > >>>>>>> that >> > >>>>>>>>> the >> > >>>>>>>>>> instance has something interesting going on. >> > >>>>>>>>>> >> > >>>>>>>>>> When I poked at things initially, I did try out having >> different >> > >>>>>>>> states, >> > >>>>>>>>>> and I readily agree that a PAUSING state may make sense. >> > >>>>> (Especially >> > >>>>>>>> if >> > >>>>>>>>>> there's a need to run commits before transitioning all the way >> > to >> > >>>>>>>>> PAUSED.) >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> And that's all I have to say about that. I hope you don't >> find >> > >> my >> > >>>>>>>>>>> long message offputting. I'm fundamentally in favor of your >> > KIP, >> > >>>>>>>>>>> and I think with a little more explanation in the KIP, and a >> > few >> > >>>>>>>>>>> small tweaks to the proposal, we'll be able to provide good >> > >>>>>>>>>>> ergonomics to our users. >> > >>>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>> Thanks! >> > >>>>>>>>>> >> > >>>>>>>>>> Jim >> > >>>>>>>>>> >> > >>>>>>>>>> >> > >>>>>>>>>>> Thanks, >> > >>>>>>>>>>> -John >> > >>>>>>>>>>> >> > >>>>>>>>>>> On Sat, May 7, 2022, at 00:06, Guozhang Wang wrote: >> > >>>>>>>>>>>> I'm in favor of the "just pausing the instance itself“ >> option >> > >>>>> as >> > >>>>>>>>> well. As >> > >>>>>>>>>>>> for EOS, the point is that when the processing is paused, we >> > >>>>> would >> > >>>>>>>> not >> > >>>>>>>>>>>> trigger any `producer.send` during the time, and the >> > >>>>> transaction >> > >>>>>>>>> timeout >> > >>>>>>>>>>> is >> > >>>>>>>>>>>> sort of relying on that behavior, so my point was that it's >> > >>>>>>> probably >> > >>>>>>>>>>> better >> > >>>>>>>>>>>> to also commit the processing before we pause it. >> > >>>>>>>>>>>> >> > >>>>>>>>>>>> >> > >>>>>>>>>>>> Guozhang >> > >>>>>>>>>>>> >> > >>>>>>>>>>>> On Fri, May 6, 2022 at 6:12 PM Jim Hughes >> > >>>>>>>>> <jhug...@confluent.io.invalid> >> > >>>>>>>>>>>> wrote: >> > >>>>>>>>>>>> >> > >>>>>>>>>>>>> Hi Matthias, >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>> Since the only thing which will be paused is processing the >> > >>>>>>>>> topology, I >> > >>>>>>>>>>>>> think we can let commits happen naturally. >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>> Good point about getting the paused state to new members; >> it >> > >>>>> is >> > >>>>>>>>> seeming >> > >>>>>>>>>>>>> like the "building block" approach is a good one to keep >> > >>>>> things >> > >>>>>>>>> simple >> > >>>>>>>>>>> at >> > >>>>>>>>>>>>> first. >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>> Cheers, >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>> Jim >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>> On Fri, May 6, 2022 at 8:31 PM Matthias J. Sax < >> > >>>>> mj...@apache.org >> > >>>>>>>> >> > >>>>>>>>>>> wrote: >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>>>> I think it's tricky to propagate a pauseAll() via the >> > >>>>> rebalance >> > >>>>>>>>>>>>>> protocol. New members joining the group would need to get >> > >>>>>>> paused, >> > >>>>>>>>> too? >> > >>>>>>>>>>>>>> Could there be weird race conditions with overlapping >> > >>>>>>> pauseAll() >> > >>>>>>>>> and >> > >>>>>>>>>>>>>> resumeAll() calls on different instanced while there could >> > >>>>> be a >> > >>>>>>>>>>> errors / >> > >>>>>>>>>>>>>> network partitions or similar? >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> I would argue that similar to IQ, we provide the basic >> > >>>>> building >> > >>>>>>>>>>> blocks, >> > >>>>>>>>>>>>>> and leave it the user users to implement cross instance >> > >>>>>>>> management >> > >>>>>>>>>>> for a >> > >>>>>>>>>>>>>> pauseAll() scenario. -- Also, if there is really demand, >> we >> > >>>>> can >> > >>>>>>>>> always >> > >>>>>>>>>>>>>> add pauseAll()/resumeAll() as follow up work. >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> About named typologies: I agree to Jim to not include them >> > >>>>> in >> > >>>>>>>> this >> > >>>>>>>>> KIP >> > >>>>>>>>>>>>>> as they are not a public feature yet. If we make named >> > >>>>>>> typologies >> > >>>>>>>>>>>>>> public, the corresponding KIP should extend the >> pause/resume >> > >>>>>>>>> feature >> > >>>>>>>>>>>>>> (ie, APIs) accordingly. Of course, the code can (and >> should) >> > >>>>>>>>> already >> > >>>>>>>>>>> be >> > >>>>>>>>>>>>>> setup to support it to be future proof. >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> Good call out about commit and EOS -- to simplify it, I >> > >>>>> think >> > >>>>>>> it >> > >>>>>>>>> might >> > >>>>>>>>>>>>>> be good to commit also for the at-least-once case? >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> -Matthias >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> On 5/6/22 1:05 PM, Jim Hughes wrote: >> > >>>>>>>>>>>>>>> Hi Bill, >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> Great questions; I'll do my best to reply inline: >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> On Fri, May 6, 2022 at 3:21 PM Bill Bejeck < >> > >>>>>>> bbej...@gmail.com> >> > >>>>>>>>>>> wrote: >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> Hi Jim, >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> Thanks for the KIP. I have a couple of meta-questions >> as >> > >>>>>>>> well: >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> 1) Regarding pausing only a subset of running instances, >> > >>>>> I'm >> > >>>>>>>>>>> thinking >> > >>>>>>>>>>>>>> there >> > >>>>>>>>>>>>>>>> may be a use case for pausing all of them. >> > >>>>>>>>>>>>>>>> Would it make sense to also allow for pausing all >> > >>>>>>>> instances >> > >>>>>>>>> by >> > >>>>>>>>>>>>>> adding a >> > >>>>>>>>>>>>>>>> method `pauseAll()` or something similar? >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> Honestly, I'm indifferent on this point. Presently, I >> > >>>>> think >> > >>>>>>>>> what I >> > >>>>>>>>>>>>> have >> > >>>>>>>>>>>>>>> proposed is the minimal change to get the ability to >> pause >> > >>>>>>> and >> > >>>>>>>>>>> resume >> > >>>>>>>>>>>>>>> processing. If adding a 'pauseAll()' is required, I'd be >> > >>>>>>> happy >> > >>>>>>>>> to >> > >>>>>>>>>>> do >> > >>>>>>>>>>>>>> that! >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> From Guozhang's email, it sounds like this would >> require >> > >>>>>>> using >> > >>>>>>>>> the >> > >>>>>>>>>>>>>>> rebalance protocol to trigger the coordination. Would >> > >>>>> there >> > >>>>>>> be >> > >>>>>>>>>>> enough >> > >>>>>>>>>>>>>> room >> > >>>>>>>>>>>>>>> in that approach to indicate that a named topology is to >> > >>>>> be >> > >>>>>>>>> paused >> > >>>>>>>>>>>>> across >> > >>>>>>>>>>>>>>> all nodes? >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> 2) Would pausing affect standby tasks? For example, >> > >>>>> imagine >> > >>>>>>>>> there >> > >>>>>>>>>>>>> are 3 >> > >>>>>>>>>>>>>>>> instances A, B, and C. >> > >>>>>>>>>>>>>>>> A user elects to pause instance C only but it >> hosts >> > >>>>> the >> > >>>>>>>>> standby >> > >>>>>>>>>>>>>> tasks >> > >>>>>>>>>>>>>>>> for A. >> > >>>>>>>>>>>>>>>> Would the standby tasks on the paused application >> > >>>>>>> continue >> > >>>>>>>>> to >> > >>>>>>>>>>> read >> > >>>>>>>>>>>>>> from >> > >>>>>>>>>>>>>>>> the changelog topic? >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> Yes, standby tasks would continue reading from the >> > >>>>> changelog >> > >>>>>>>>> topic. >> > >>>>>>>>>>>>> All >> > >>>>>>>>>>>>>>> consumers would continue reading to avoid getting dropped >> > >>>>>>> from >> > >>>>>>>>> their >> > >>>>>>>>>>>>>>> consumer groups. >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> Cheers, >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> Jim >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> Thanks! >> > >>>>>>>>>>>>>>>> Bill >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> On Fri, May 6, 2022 at 2:44 PM Jim Hughes >> > >>>>>>>>>>>>> <jhug...@confluent.io.invalid >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> wrote: >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Hi Guozhang, >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Thanks for the feedback; responses inline below: >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> On Fri, May 6, 2022 at 1:09 PM Guozhang Wang < >> > >>>>>>>>> wangg...@gmail.com> >> > >>>>>>>>>>>>>> wrote: >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> Hello Jim, >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> Thanks for the proposed KIP. I have some meta >> questions >> > >>>>>>>> about >> > >>>>>>>>> it: >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> 1) Would an instance always pause/resume all of its >> > >>>>>>> current >> > >>>>>>>>> owned >> > >>>>>>>>>>>>>>>>>> topologies (i.e. the named topologies), or are there >> > >>>>> any >> > >>>>>>>>>>> scenarios >> > >>>>>>>>>>>>>>>> where >> > >>>>>>>>>>>>>>>>> we >> > >>>>>>>>>>>>>>>>>> only want to pause/resume a subset of them? >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> An instance may wish to pause some of its named >> > >>>>> topologies. >> > >>>>>>>> I >> > >>>>>>>>> was >> > >>>>>>>>>>>>>> unsure >> > >>>>>>>>>>>>>>>>> what to say about named topologies in the KIP since >> they >> > >>>>>>> seem >> > >>>>>>>>> to >> > >>>>>>>>>>> be >> > >>>>>>>>>>>>> an >> > >>>>>>>>>>>>>>>>> internal detail at the moment. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> I intend to add to KafkaStreamsNamedTopologyWrapper >> > >>>>> methods >> > >>>>>>>>> like: >> > >>>>>>>>>>>>>>>>> public void pauseNamedTopology(final String >> > >>>>>>>>> topologyToPause) >> > >>>>>>>>>>>>>>>>> public boolean isNamedTopologyPaused(final >> String >> > >>>>>>>>> topology) >> > >>>>>>>>>>>>>>>>> public void resumeNamedTopology(final String >> > >>>>>>>>>>> topologyToResume) >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> 2) From a user's perspective, do we want to always >> > >>>>> issue a >> > >>>>>>>>>>>>>>>> `pause/resume` >> > >>>>>>>>>>>>>>>>>> to all the instances or not? For example, we can >> define >> > >>>>>>> the >> > >>>>>>>>>>>>> semantics >> > >>>>>>>>>>>>>>>> of >> > >>>>>>>>>>>>>>>>>> the function as "you only need to call this function >> on >> > >>>>>>> any >> > >>>>>>>> of >> > >>>>>>>>>>> the >> > >>>>>>>>>>>>>>>>>> application's instances, and all instances would then >> > >>>>>>> pause >> > >>>>>>>>> (via >> > >>>>>>>>>>> the >> > >>>>>>>>>>>>>>>>>> rebalance error codes)", or as "you would call this >> > >>>>>>> function >> > >>>>>>>>> for >> > >>>>>>>>>>> all >> > >>>>>>>>>>>>>>>> the >> > >>>>>>>>>>>>>>>>>> instances of an application". Which one are you >> > >>>>> referring >> > >>>>>>>> to? >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> My initial intent is that one would call this function >> > >>>>> on >> > >>>>>>> any >> > >>>>>>>>>>>>> instances >> > >>>>>>>>>>>>>>>> of >> > >>>>>>>>>>>>>>>>> the application that one wishes to pause. This should >> > >>>>>>> allow >> > >>>>>>>>> more >> > >>>>>>>>>>>>>> control >> > >>>>>>>>>>>>>>>>> (in case one wanted to pause a portion of the >> > >>>>> instances). >> > >>>>>>> On >> > >>>>>>>>> the >> > >>>>>>>>>>>>> other >> > >>>>>>>>>>>>>>>>> hand, this approach would put more work on the >> > >>>>> implementer >> > >>>>>>> to >> > >>>>>>>>>>>>>> coordinate >> > >>>>>>>>>>>>>>>>> calling pause or resume across instances. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> If the other option is more suitable, happy to do that >> > >>>>>>>> instead. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> 3) With EOS, there's a transaction timeout which would >> > >>>>>>>>> determine >> > >>>>>>>>>>> how >> > >>>>>>>>>>>>>>>>> long a >> > >>>>>>>>>>>>>>>>>> transaction can stay idle before it's force-aborted on >> > >>>>> the >> > >>>>>>>>> broker >> > >>>>>>>>>>>>>>>> side. I >> > >>>>>>>>>>>>>>>>>> think when a pause is issued, that means we'd need to >> > >>>>>>>>> immediately >> > >>>>>>>>>>>>>>>> commit >> > >>>>>>>>>>>>>>>>>> the current transaction for EOS since we do not know >> > >>>>> how >> > >>>>>>>> long >> > >>>>>>>>> we >> > >>>>>>>>>>>>> could >> > >>>>>>>>>>>>>>>>>> pause for. Is that right? If yes could you please >> > >>>>> clarify >> > >>>>>>>>> that in >> > >>>>>>>>>>>>> the >> > >>>>>>>>>>>>>>>> doc >> > >>>>>>>>>>>>>>>>>> as well. >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Good point. My intent is for pause() to wait for the >> > >>>>> next >> > >>>>>>>>>>> iteration >> > >>>>>>>>>>>>>>>>> through `runOnce()` and then only skip over the >> > >>>>> processing >> > >>>>>>>> for >> > >>>>>>>>>>> paused >> > >>>>>>>>>>>>>>>> tasks >> > >>>>>>>>>>>>>>>>> in `taskManager.process(numIterations, time)`. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Do commits live inside that call or do they live >> > >>>>>>>>> across/outside of >> > >>>>>>>>>>>>> it? >> > >>>>>>>>>>>>>>>> In >> > >>>>>>>>>>>>>>>>> the former case, I think there shouldn't be any issues >> > >>>>> with >> > >>>>>>>>> EOS. >> > >>>>>>>>>>>>>>>>> Otherwise, we may need to work through some details to >> > >>>>> get >> > >>>>>>>> EOS >> > >>>>>>>>>>> right. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Once we figure that out, I can update the KIP. >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Thanks, >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> Jim >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> Guozhang >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> On Wed, May 4, 2022 at 10:51 AM Jim Hughes >> > >>>>>>>>>>>>>>>> <jhug...@confluent.io.invalid >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> wrote: >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>>> Hi all, >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>>> I have written up a KIP for adding the ability to >> > >>>>> pause >> > >>>>>>> and >> > >>>>>>>>>>> resume >> > >>>>>>>>>>>>>>>> the >> > >>>>>>>>>>>>>>>>>>> processing of a topology in AK Streams. The KIP is >> > >>>>> here: >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>> >> > >>>>>>>>>>> >> > >>>>>>>>> >> > >>>>>>>> >> > >>>>>>> >> > >>>>> >> > >>> >> > >> >> > >> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=211882832 >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>>> Thanks in advance for your feedback! >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>>> Cheers, >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>>> Jim >> > >>>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>>> -- >> > >>>>>>>>>>>>>>>>>> -- Guozhang >> > >>>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>>> >> > >>>>>>>>>>>>>> >> > >>>>>>>>>>>>> >> > >>>>>>>>>>>> >> > >>>>>>>>>>>> >> > >>>>>>>>>>>> -- >> > >>>>>>>>>>>> -- Guozhang >> > >>>>>>>>>>> >> > >>>>>>>>> >> > >>>>>>>> >> > >>>>>>>> >> > >>>>>>>> -- >> > >>>>>>>> -- Guozhang >> > >>>>>>>> >> > >>>>>>> >> > >>>>> >> > >>>> >> > >>> >> > >> >> > > >> > >>
