Hi John, I agree with you. It is better to measure the metric on processor node level. The users can do the rollup to task-level by themselves.
Best, Bruno On Thu, Feb 27, 2020 at 12:09 AM John Roesler <vvcep...@apache.org> wrote: > > Hi Richard, > > I've been making a final pass over the KIP. > > Re: Proposed Behavior Change: > > I think this point is controversial and probably doesn't need to be there at > all: > > 2.b. In certain situations where there is a high volume of idempotent > > updates throughout the Streams DAG, it will be recommended practice > > to materialize all operations to reduce traffic overall across the entire > > network of nodes. > > Re-reading all the points, it seems like we can sum them up in a way that's > a little more straight to the point, and gives us the right amount of > flexibility: > > > Proposed Behavior Changes > > > > Definition: "idempotent update" is one in which the new result and prior > > result, when serialized, are identical byte arrays > > > > Note: an "update" is a concept that only applies to Table operations, so > > the concept of an "idempotent update" also only applies to Table operations. > > See > > https://kafka.apache.org/documentation/streams/developer-guide/dsl-api.html#streams_concepts_ktable > > for more information. > > > > Given that definition, we propose for Streams to drop idempotent updates > > in any situation where it's possible and convenient to do so. For example, > > any time we already have both the prior and new results serialized, we > > may compare them, and drop the update if it is idempotent. > > > > Note that under this proposal, we can implement idempotence checking > > in the following situations: > > 1. Any aggregation (for example, KGroupedStream, KGroupedTable, > > TimeWindowedKStream, and SessionWindowedKStream operations) > > 2. Any Materialized KTable operation > > 3. Repartition operations, when we need to send both prior and new results > > Notice that in my proposed wording, we neither limit ourselves to just the > situations enumerated, nor promise to implement the optimization in every > possible situation. IMHO, this is the best way to propose such a feature. > That way, we have the flexibility to implement it in stages, and also to add > on to the implementation in the future. > > > Re: Metrics > > I agree with Bruno, although, I think it might just be a confusing statement. > It might be clearer to drop all the "discussion", and just say: "We will add a > metric to count the number of idempotent updates that we have dropped". > > Also, with respect to the metric, I'm wondering if the metric should be task- > level or processor-node-level. Since the interesting action takes place inside > individual processor nodes, I _think_ it would be higher leverage to just > measure it at the node level. WDYT? > > Re: Design Reasoning > > This section seems to be a little bit outdated. I also just noticed a > "surprise" > configuration "timestamp.aggregation.selection.policy" hidden in point 1.a. > Is that part of the proposal? We haven't discussed it, and I think we were > talking about this KIP being "configuration free". > > There is also some discussion of discarded alternative in the Design Reasoning > section, which is confusing. Finally, there was a point there I didn't > understand > at all, about stateless operators not being intended to load prior results. > This statement doesn't seem to be true, but it also doesn't seem to be > relevant, > so maybe we can just drop it. > > Overall, it might help if you make a pass on this section, and just discuss as > briefly as possible the justification for the proposed behavior change, and > not adding a configuration. Try to avoid talking about things that we are not > proposing, since that will just lead to confusion. > > Similarly, I'd just completely remove the "Implementation [discarded]" > section. > It was good to have this as part of the discussion initially, but as we move > toward a vote, it's better to just streamline the KIP document as much as > possible. Keeping a "discarded" section in the document will just make it > harder for new people to understand the proposal. We did the same thing > with KIP-441, where there were two prior drafts included at the end of the > document, and we just deleted them for clarity. > > I liked the "Compatibility" and "Rejected Alternatives" section. Very clear > and to the point. > > Thanks again for the contribution! I think once the KIP document is cleaned > up, we'll be in good shape to finalize the discussion. > -John > > > On Wed, Feb 26, 2020, at 07:27, Bruno Cadonna wrote: > > Hi Richard, > > > > 1. Could you change "idempotent update operations will only be dropped > > from KTables, not from other classes." -> idempotent update operations > > will only be dropped from materialized KTables? For non-materialized > > KTables -- as they can occur after optimization of the topology -- we > > cannot drop idempotent updates. > > > > 2. I cannot completely follow the metrics section. Do you want to > > record all idempotent updates or only the dropped ones? In particular, > > I do not understand the following sentences: > > "For that matter, even if we don't drop idempotent updates, we should > > at the very least record the number of idempotent updates that has > > been seen go through a particular processor." > > "Therefore, we should add some metrics which will count the number of > > idempotent updates that each node has seen." > > I do not see how we can record idempotent updates that we do not drop. > > If we see them, we should drop them. If we do not see them, we cannot > > drop them and we cannot record them. > > > > Best, > > Bruno > > > > On Wed, Feb 26, 2020 at 4:57 AM Richard Yu <yohan.richard...@gmail.com> > > wrote: > > > > > > Hi John, > > > > > > Sounds goods. It looks like we are close to wrapping things up. If there > > > isn't any other revisions which needs to be made. (If so, please comment > > > in > > > the thread) > > > I will start the voting process this Thursday (Pacific Standard Time). > > > > > > Cheers, > > > Richard > > > > > > On Tue, Feb 25, 2020 at 11:59 AM John Roesler <vvcep...@apache.org> wrote: > > > > > > > Hi Richard, > > > > > > > > Sorry for the slow reply. I actually think we should avoid checking > > > > equals() for now. Your reasoning is good, but the truth is that > > > > depending on the implementation of equals() is non-trivial, > > > > semantically, and (though I proposed it before), I'm not convinced > > > > it's worth the risk. Much better to start with exactly one kind of > > > > "idempotence detection". > > > > > > > > Even if someone does update their serdes, we know that the new > > > > serde would still be able to _de_serialize the old format, or the whole > > > > app would break. The situation is that the new result gets encoded > > > > in the new binary format, which means we don't detect an idempotent > > > > update for what it is. In this case, we'd write the new binary format to > > > > disk and the changelog, and forward it downstream. However, we only > > > > do this once. Now that the binary format for that record has been > > > > updated, > > > > we would correctly detect idempotence of any subsequent updates. > > > > > > > > Plus, we would still be able to filter out idempotent updates in > > > > repartition > > > > sinks, since for those, we use the new serde to serialize both the "old" > > > > and > > > > "new" result. > > > > > > > > It's certainly a good observation, but I think we can just make a note > > > > of > > > > it > > > > in "rejected alternatives" for now, and plan to refine it later, if it > > > > does > > > > pose a big performance problem. > > > > > > > > Thanks! > > > > -John > > > > > > > > On Sat, Feb 22, 2020, at 18:14, Richard Yu wrote: > > > > > Hi all, > > > > > > > > > > Updated the KIP. > > > > > > > > > > Just a question: do you think it would be a good idea if we check for > > > > both > > > > > Object#equals() and binary equality? > > > > > Because there might be some subtle changes in the serialization (for > > > > > example, if the user decides to upgrade their serialization procedure > > > > > to > > > > a > > > > > new one), but the underlying values of the result might be the same. > > > > > (therefore equals() might return true) > > > > > > > > > > Do you think this would be plausible? > > > > > > > > > > Cheers, > > > > > Richard > > > > > > > > > > On Fri, Feb 21, 2020 at 2:37 PM Richard Yu > > > > > <yohan.richard...@gmail.com> > > > > > wrote: > > > > > > > > > > > Hello, > > > > > > > > > > > > Just to make some updates. I changed the name of the metric so that > > > > > > it > > > > was > > > > > > more in line with usual Kafka naming conventions for metrics / > > > > > > sensors. > > > > > > Below is the updated description of the metric: > > > > > > > > > > > > dropped-idempotent-updates : (Level 2 - Per Task) DEBUG (rate | > > > > > > total) > > > > > > > > > > > > Description: This metric will record the number of updates that have > > > > been > > > > > > dropped since they are essentially re-performing an earlier > > > > > > operation. > > > > > > > > > > > > Note: > > > > > > > > > > > > - The rate option indicates the ratio of records dropped to > > > > > > actual > > > > > > volume of records passing through the task. > > > > > > - The total option will just give a raw count of the number of > > > > records > > > > > > dropped. > > > > > > > > > > > > > > > > > > I hope that this is more on point. > > > > > > > > > > > > Best, > > > > > > Richard > > > > > > > > > > > > On Fri, Feb 21, 2020 at 2:20 PM Richard Yu > > > > > > <yohan.richard...@gmail.com > > > > > > > > > > > wrote: > > > > > > > > > > > >> Hi all, > > > > > >> > > > > > >> Thanks for the clarification. I was just confused a little on what > > > > > >> was > > > > > >> going on. > > > > > >> > > > > > >> So I guess then that for the actual proposal. We got the following: > > > > > >> > > > > > >> 1. We check for binary equality, and perform no extra look ups. > > > > > >> 2. Emphasize that this applies only to materialized tables. > > > > > >> 3. We drop aggregation updates if key, value and timestamp is the > > > > same. > > > > > >> > > > > > >> Then that settles the behavior changes. So it looks like the Metric > > > > that > > > > > >> is the only thing that is left. In this case, I think the metric > > > > would be > > > > > >> named the following: IdempotentUpdateMetric. This is mostly off the > > > > top of > > > > > >> my head. So if you think that we change it, feel free to say so. > > > > > >> The metric will report the number of dropped operations inherently. > > > > > >> > > > > > >> It will probably be added as a Sensor, similar to the dropped > > > > > >> records > > > > > >> sensor we already have. > > > > > >> > > > > > >> If there isn't anything else, I will probably start the voting > > > > > >> process > > > > > >> next week! > > > > > >> > > > > > >> Cheers, > > > > > >> Richard > > > > > >> > > > > > >> > > > > > >> On Fri, Feb 21, 2020 at 11:23 AM John Roesler <vvcep...@apache.org> > > > > > >> wrote: > > > > > >> > > > > > >>> Hi Bruno, > > > > > >>> > > > > > >>> Thanks for the clarification. Indeed, I was thinking two things: > > > > > >>> 1. For the initial implementation, we can just avoid adding any > > > > > >>> extra > > > > > >>> lookups, but only do the comparison when we already happen to have > > > > > >>> the prior value. > > > > > >>> 2. I think, as a result of the timestamp semantics, we actually > > > > > >>> _do_ > > > > look > > > > > >>> up the prior value approximately all the time, so the idempotence > > > > check > > > > > >>> should be quite effective. > > > > > >>> > > > > > >>> I think that second point is the same thing you're referring to > > > > > >>> potentially > > > > > >>> being unnecessary. It does mean that we do fetch the whole value > > > > > >>> in a > > > > > >>> lot of cases where we really only need the timestamp, so it could > > > > > >>> certainly > > > > > >>> be optimized in the future. In that future, we would need to weigh > > > > that > > > > > >>> optimization against losing the idempotence check. But, that's a > > > > problem > > > > > >>> for tomorrow :) > > > > > >>> > > > > > >>> I'm 100% on board with scrutinizing the performance as we > > > > > >>> implement > > > > > >>> this feature. > > > > > >>> > > > > > >>> Thanks again, > > > > > >>> -John > > > > > >>> > > > > > >>> On Thu, Feb 20, 2020, at 03:25, Bruno Cadonna wrote: > > > > > >>> > Hi John, > > > > > >>> > > > > > > >>> > I am glad to help you with your imagination. With overhead, I > > > > mainly > > > > > >>> > meant the additional lookup into the state store to get the > > > > > >>> > current > > > > > >>> > value, but I see now in the code that we do that lookup anyways > > > > > >>> > (although I think we could avoid that in the cases where we do > > > > > >>> > not > > > > > >>> > need the old value). With or without config, we need to evaluate > > > > the > > > > > >>> > performance benefits of this change, in any case. > > > > > >>> > > > > > > >>> > Best, > > > > > >>> > Bruno > > > > > >>> > > > > > > >>> > On Wed, Feb 19, 2020 at 7:48 PM John Roesler > > > > > >>> > <vvcep...@apache.org> > > > > > >>> wrote: > > > > > >>> > > > > > > > >>> > > Thanks for your remarks, Bruno! > > > > > >>> > > > > > > > >>> > > I'm in favor of standardizing on terminology like "not > > > > > >>> > > forwarding > > > > > >>> > > idempotent updates" or "dropping idempotent updates". Maybe we > > > > > >>> > > should make a pass on the KIP and just convert everything to > > > > > >>> > > this > > > > > >>> > > phrasing. In retrospect, even the term "emit-on-change" has > > > > > >>> > > too > > > > much > > > > > >>> > > semantic baggage, since it implies the semantics from the > > > > > >>> > > SECRET > > > > > >>> > > paper, which we don't really want to imply here. > > > > > >>> > > > > > > > >>> > > I'm also in favor of the metric as you propose. > > > > > >>> > > > > > > > >>> > > Likewise with stream aggregations, I was also under the > > > > impression > > > > > >>> > > that we agreed on dropping idempotent updates to the > > > > > >>> > > aggregation > > > > > >>> > > result, any time we find that our "new" (key, value, > > > > > >>> > > timestamp) > > > > > >>> result > > > > > >>> > > is identical to the prior one. > > > > > >>> > > > > > > > >>> > > Also, I'm +1 on all your recommendations for updating the KIP > > > > > >>> document > > > > > >>> > > for clarity. > > > > > >>> > > > > > > > >>> > > Regarding the opt-out config. Perhaps I'm suffering from a > > > > failure of > > > > > >>> > > imagination, but I don't see how the current proposal could > > > > really > > > > > >>> have > > > > > >>> > > a measurable impact on latency. If all we do is make a single > > > > extra > > > > > >>> pass > > > > > >>> > > to compare two byte arrays for equality, only in the cases > > > > > >>> > > where > > > > we > > > > > >>> already > > > > > >>> > > have the byte arrays available, it seems unlikely to > > > > > >>> > > measurably > > > > > >>> affect the > > > > > >>> > > processing of non-idempotent updates. It seems guaranteed to > > > > > >>> _decrease_ > > > > > >>> > > the latency of processing idempotent updates, since we get to > > > > skip a > > > > > >>> > > store#put, at least one producer#send, and also all downstream > > > > > >>> processing, > > > > > >>> > > including all the disk and network operations associated with > > > > > >>> downstream > > > > > >>> > > operations. > > > > > >>> > > > > > > > >>> > > It seems like if we're pretty sure this change would only > > > > _help_, we > > > > > >>> shouldn't > > > > > >>> > > introduce the operational burden of an extra configuration. > > > > > >>> > > If we > > > > > >>> want to > > > > > >>> > > be more aggressive about dropping idempotent operations in the > > > > > >>> future, > > > > > >>> > > such as depending on equals() or adding a ChangeDetector > > > > interface, > > > > > >>> then > > > > > >>> > > we should consider adding a configuration as part of that > > > > > >>> > > future > > > > > >>> work. In > > > > > >>> > > fact, if we add a simple "opt-in/opt-out" switch right now, we > > > > might > > > > > >>> find > > > > > >>> > > that it's actually insufficient for whatever future feature we > > > > might > > > > > >>> propose, > > > > > >>> > > then we have a mess of deprecating the opt-out config and > > > > replacing > > > > > >>> it. > > > > > >>> > > > > > > > >>> > > What do you think? > > > > > >>> > > -John > > > > > >>> > > > > > > > >>> > > On Wed, Feb 19, 2020, at 09:50, Bruno Cadonna wrote: > > > > > >>> > > > Hi all, > > > > > >>> > > > > > > > > >>> > > > Sorry for the late reply! > > > > > >>> > > > > > > > > >>> > > > I am also in favour of baby steps. > > > > > >>> > > > > > > > > >>> > > > I am undecided whether the KIP should contain a opt-out > > > > > >>> > > > config > > > > or > > > > > >>> not. > > > > > >>> > > > The overhead of emit-on-change might affect latency. For > > > > > >>> applications > > > > > >>> > > > where low latency is crucial and there are not too many > > > > idempotent > > > > > >>> > > > updates, it would be better to fall back to emit-on-update. > > > > > >>> However, > > > > > >>> > > > we do not know how much emit-on-change impacts latency. We > > > > would > > > > > >>> first > > > > > >>> > > > need to benchmark that before we can decide about the > > > > > >>> opt-out-config. > > > > > >>> > > > > > > > > >>> > > > A metric of dropped idempotent updates seems useful to me > > > > > >>> > > > to be > > > > > >>> > > > informed about potential upstream applications or upstream > > > > > >>> operators > > > > > >>> > > > that produce too many idempotent updates. The KIP should > > > > > >>> > > > state > > > > the > > > > > >>> > > > name of the metric, its group, its tags, and its recording > > > > level > > > > > >>> (see > > > > > >>> > > > KIP-444 or KIP-471 for examples). I propose DEBUG as > > > > > >>> > > > reporting > > > > > >>> level. > > > > > >>> > > > > > > > > >>> > > > Richard, what competing proposals for emit-on-change for > > > > > >>> aggregations > > > > > >>> > > > do you mean? I have the feeling that we agreed to get rid of > > > > > >>> > > > idempotent updates if the aggregate is updated with the same > > > > key, > > > > > >>> > > > value, AND timestamp. I am also fine if we do not include > > > > > >>> > > > this > > > > into > > > > > >>> > > > this KIP (remember: baby steps). > > > > > >>> > > > > > > > > >>> > > > You write that "emit-on-change is more correct". Since we > > > > agreed > > > > > >>> that > > > > > >>> > > > this is an optimization, IMO you cannot argue this way. > > > > > >>> > > > > > > > > >>> > > > Please put "Alternative Approaches" under "Rejected > > > > Alternatives", > > > > > >>> so > > > > > >>> > > > that it becomes clear that we are not going to implement > > > > > >>> > > > them. > > > > In > > > > > >>> > > > general, I think the KIP needs a bit of clean-up (probably, > > > > > >>> > > > you > > > > > >>> > > > already planned for it). "Design Reasoning" is a bit of > > > > behavior > > > > > >>> > > > changes, rejected alternatives and duplicates a bit the > > > > content in > > > > > >>> > > > those sections. > > > > > >>> > > > > > > > > >>> > > > I do not like the name "no-op operations" or "no-ops", > > > > > >>> > > > because > > > > they > > > > > >>> > > > are rather generic. I like more "idempotent updates". > > > > > >>> > > > > > > > > >>> > > > Best, > > > > > >>> > > > Bruno > > > > > >>> > > > > > > > > >>> > > > > > > > > >>> > > > On Tue, Feb 18, 2020 at 7:25 PM Richard Yu < > > > > > >>> yohan.richard...@gmail.com> wrote: > > > > > >>> > > > > > > > > > >>> > > > > Hi all, > > > > > >>> > > > > > > > > > >>> > > > > We are definitely making progress! > > > > > >>> > > > > > > > > > >>> > > > > @John should I emphasize in the proposed behavior changes > > > > that > > > > > >>> we are only > > > > > >>> > > > > doing binary equality checks for stateful operators? > > > > > >>> > > > > It looks like we have come close to finalizing this part > > > > > >>> > > > > of > > > > the > > > > > >>> KIP. (I > > > > > >>> > > > > will note in the KIP that this proposal is intended for > > > > > >>> optimization, not > > > > > >>> > > > > semantics correctness) > > > > > >>> > > > > > > > > > >>> > > > > I do think maybe we still have one other detail we need to > > > > > >>> discuss. So far, > > > > > >>> > > > > there has been quite a bit of back and forth about what > > > > > >>> > > > > the > > > > > >>> behavior of > > > > > >>> > > > > aggregations should look like in emit on change. I have > > > > > >>> > > > > seen > > > > > >>> > > > > multiple competing proposals, so I am not completely > > > > > >>> > > > > certain > > > > > >>> which one we > > > > > >>> > > > > should go with, or how we will be able to compromise in > > > > between > > > > > >>> them. > > > > > >>> > > > > > > > > > >>> > > > > Let me know what your thoughts are on this matter, since > > > > > >>> > > > > we > > > > are > > > > > >>> probably > > > > > >>> > > > > close to wrapping up most other stuff. > > > > > >>> > > > > @Matthias J. Sax <matth...@confluent.io> and @Bruno, see > > > > what > > > > > >>> you think > > > > > >>> > > > > about this. > > > > > >>> > > > > > > > > > >>> > > > > Best, > > > > > >>> > > > > Richard > > > > > >>> > > > > > > > > > >>> > > > > > > > > > >>> > > > > > > > > > >>> > > > > On Tue, Feb 18, 2020 at 9:06 AM John Roesler < > > > > > >>> vvcep...@apache.org> wrote: > > > > > >>> > > > > > > > > > >>> > > > > > Thanks, Matthias! > > > > > >>> > > > > > > > > > > >>> > > > > > Regarding numbers, it would be hard to know how many > > > > > >>> applications > > > > > >>> > > > > > would benefit, since we don't know how many applications > > > > there > > > > > >>> are, > > > > > >>> > > > > > or anything about their data sets or topologies. We > > > > > >>> > > > > > could > > > > do a > > > > > >>> survey, > > > > > >>> > > > > > but it seems overkill if we take the conservative > > > > > >>> > > > > > approach. > > > > > >>> > > > > > > > > > > >>> > > > > > I have my own practical stream processing experience > > > > > >>> > > > > > that > > > > > >>> tells me this > > > > > >>> > > > > > is absolutely critical for any moderate-to-large > > > > > >>> > > > > > relational > > > > > >>> stream > > > > > >>> > > > > > processing use cases. I'll leave it to you to decide if > > > > > >>> > > > > > you > > > > > >>> find that > > > > > >>> > > > > > convincing, but it's definitely not an _assumption_. > > > > > >>> > > > > > I've > > > > also > > > > > >>> heard from > > > > > >>> > > > > > a few Streams users who have already had to implement > > > > their own > > > > > >>> > > > > > noop-suppression transformers in order to get to > > > > > >>> > > > > > production > > > > > >>> scale. > > > > > >>> > > > > > > > > > > >>> > > > > > Regardless, it sounds like we can agree on taking an > > > > > >>> opportunistic approach > > > > > >>> > > > > > and targeting the optimization just to use a > > > > binary-equality > > > > > >>> check at > > > > > >>> > > > > > stateful operators. (I'd also suggest in sink nodes, > > > > > >>> > > > > > when > > > > we > > > > > >>> are about to > > > > > >>> > > > > > send old and new values, since they are also already > > > > present > > > > > >>> and serialized > > > > > >>> > > > > > at that point.) We could make the KIP even more vague, > > > > > >>> > > > > > and > > > > > >>> just say that > > > > > >>> > > > > > we'll drop no-op updates "when possible". > > > > > >>> > > > > > > > > > > >>> > > > > > I'm curious what Bruno and the others think about this. > > > > > >>> > > > > > If > > > > it > > > > > >>> seems like > > > > > >>> > > > > > a good starting point, perhaps we could move to a vote > > > > > >>> > > > > > soon > > > > > >>> and get to > > > > > >>> > > > > > work on the implementation! > > > > > >>> > > > > > > > > > > >>> > > > > > Thanks, > > > > > >>> > > > > > -John > > > > > >>> > > > > > > > > > > >>> > > > > > On Mon, Feb 17, 2020, at 20:54, Matthias J. Sax wrote: > > > > > >>> > > > > > > Talking about optimizations and reducing downstream > > > > > >>> > > > > > > load: > > > > > >>> > > > > > > > > > > > >>> > > > > > > Do we actually have any numbers? I have the impression > > > > that > > > > > >>> this KIP is > > > > > >>> > > > > > > more or less build on the _assumption_ that there is a > > > > > >>> problem. Yes, > > > > > >>> > > > > > > there are some use cases that would benefit from this; > > > > But > > > > > >>> how many > > > > > >>> > > > > > > applications would actually benefit? And how much load > > > > > >>> reduction would > > > > > >>> > > > > > > they get? > > > > > >>> > > > > > > > > > > > >>> > > > > > > The simplest approach (following John idea to make > > > > > >>> > > > > > > baby > > > > > >>> steps) would be > > > > > >>> > > > > > > to apply the emit-on-change pattern only if there is a > > > > > >>> store. For this > > > > > >>> > > > > > > case we need to serialize old and new result anyway > > > > > >>> > > > > > > and > > > > thus > > > > > >>> a simple > > > > > >>> > > > > > > byte-array comparison is no overhead. > > > > > >>> > > > > > > > > > > > >>> > > > > > > Sending `oldValues` by default would become expensive > > > > > >>> because we would > > > > > >>> > > > > > > need to serialize the recomputed old result, as well > > > > > >>> > > > > > > as > > > > the > > > > > >>> new result, > > > > > >>> > > > > > > to make the comparison (and we now the serialization > > > > > >>> > > > > > > is > > > > not > > > > > >>> cheap). We > > > > > >>> > > > > > > are facing a trade-off between CPU overhead and > > > > downstream > > > > > >>> load and I am > > > > > >>> > > > > > > not sure if we should hard code this. My original > > > > argument > > > > > >>> for sending > > > > > >>> > > > > > > `oldValues` was about semantics; but for an > > > > optimization, I > > > > > >>> am not sure > > > > > >>> > > > > > > if this would be the right choice. > > > > > >>> > > > > > > > > > > > >>> > > > > > > For now, users who want to opt-in can force a > > > > > >>> materialization. A > > > > > >>> > > > > > > materialization may be expensive and if we see future > > > > > >>> demand, we could > > > > > >>> > > > > > > still add an option to send `oldValues` instead of > > > > > >>> materialization (this > > > > > >>> > > > > > > would at least save the store overhead). As we > > > > > >>> > > > > > > consider > > > > the > > > > > >>> KIP an > > > > > >>> > > > > > > optimization, a "config" seems to make sense. > > > > > >>> > > > > > > > > > > > >>> > > > > > > > > > > > >>> > > > > > > -Matthias > > > > > >>> > > > > > > > > > > > >>> > > > > > > > > > > > >>> > > > > > > On 2/17/20 5:21 PM, Richard Yu wrote: > > > > > >>> > > > > > > > Hi John! > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Thanks for the reply. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > About the changes we have discussed so far. I think > > > > upon > > > > > >>> further > > > > > >>> > > > > > > > consideration, we have been mostly talking about > > > > > >>> > > > > > > > this > > > > from > > > > > >>> the > > > > > >>> > > > > > perspective > > > > > >>> > > > > > > > that no stop-gap effort is acceptable. However, in > > > > recent > > > > > >>> discussion, > > > > > >>> > > > > > > if we > > > > > >>> > > > > > > > consider optimization, then it appears that the > > > > > >>> perspective I > > > > > >>> > > > > > mentioned no > > > > > >>> > > > > > > > longer applies. After all, we are no longer > > > > > >>> > > > > > > > concerned > > > > so > > > > > >>> much about > > > > > >>> > > > > > > > semantics correctness, then reducing traffic as > > > > > >>> > > > > > > > much as > > > > > >>> possible > > > > > >>> > > > > > without > > > > > >>> > > > > > > > performance tradeoffs. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > In this case, I think a cache would be a good idea > > > > > >>> > > > > > > > for > > > > > >>> stateless > > > > > >>> > > > > > > > operations. This cache will not be backed by a store > > > > > >>> obviously. We can > > > > > >>> > > > > > > > probably use Kafka's ThreadCache. We should be able > > > > > >>> > > > > > > > to > > > > > >>> catch a large > > > > > >>> > > > > > > > portion of the no-ops if we at least store some > > > > results in > > > > > >>> the cache. > > > > > >>> > > > > > Not > > > > > >>> > > > > > > > all will be caught, but I think the impact will be > > > > > >>> significant. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > On another note, I think that we should implement > > > > > >>> competing proposals > > > > > >>> > > > > > i.e. > > > > > >>> > > > > > > > one where we forward both old and new values with a > > > > > >>> reasonable > > > > > >>> > > > > > proportion > > > > > >>> > > > > > > > of artificial no-ops (we do not necessarily have to > > > > rely > > > > > >>> on equals so > > > > > >>> > > > > > much > > > > > >>> > > > > > > > as comparing the serialized binary data after the > > > > > >>> operation), and in > > > > > >>> > > > > > > > another scenario, the cache for stateless ops. It > > > > would be > > > > > >>> > > > > > unreasonable if > > > > > >>> > > > > > > > we completely disregard either approach, since they > > > > both > > > > > >>> have merit. > > > > > >>> > > > > > The > > > > > >>> > > > > > > > reason for implementing both is to perform benchmark > > > > tests > > > > > >>> on them, and > > > > > >>> > > > > > > > compare them with the original. This way, we can > > > > > >>> > > > > > > > more > > > > > >>> clearly see what > > > > > >>> > > > > > is > > > > > >>> > > > > > > > the drawbacks and the gains. So far, we have been > > > > > >>> discussing only > > > > > >>> > > > > > > > hypotheticals, and if we continue to do so, I think > > > > > >>> > > > > > > > it > > > > is > > > > > >>> likely no > > > > > >>> > > > > > ground > > > > > >>> > > > > > > > will be gained. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > After all, what we seek is optimization, and > > > > performance > > > > > >>> benchmarks > > > > > >>> > > > > > > will be > > > > > >>> > > > > > > > mandatory for a KIP of this nature. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Hope this helps, > > > > > >>> > > > > > > > Richard > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > On Mon, Feb 17, 2020 at 2:12 PM John Roesler < > > > > > >>> vvcep...@apache.org> > > > > > >>> > > > > > wrote: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >> Hi again, all, > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> Sorry on my part for my silence. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> I've just taken another look over the recent > > > > > >>> > > > > > > >> history > > > > of > > > > > >>> this > > > > > >>> > > > > > > discussion. It > > > > > >>> > > > > > > >> seems like the #1 point to clarify (because it > > > > > >>> > > > > > > >> affect > > > > > >>> everything > > > > > >>> > > > > > else) is > > > > > >>> > > > > > > >> that, > > > > > >>> > > > > > > >> yes, I was 100% envisioning this as an > > > > > >>> > > > > > > >> _optimization_. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> As a consequence, I don't think it's critical to > > > > > >>> > > > > > > >> make > > > > any > > > > > >>> hard > > > > > >>> > > > > > guarantees > > > > > >>> > > > > > > >> about > > > > > >>> > > > > > > >> what results get forwarded and what (no-op updates) > > > > get > > > > > >>> dropped. I'd > > > > > >>> > > > > > > >> initially > > > > > >>> > > > > > > >> just been thinking about doing this > > > > > >>> > > > > > > >> opportunistically > > > > in > > > > > >>> cases where > > > > > >>> > > > > > we > > > > > >>> > > > > > > >> already > > > > > >>> > > > > > > >> had the "old" and "new" result in memory, thanks > > > > > >>> > > > > > > >> to a > > > > > >>> request to > > > > > >>> > > > > > > "emit old > > > > > >>> > > > > > > >> values", or to the implementation of timestamp > > > > semantics. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> However, whether or not it's semantically > > > > > >>> > > > > > > >> critical, I > > > > do > > > > > >>> think that > > > > > >>> > > > > > > >> Matthias's > > > > > >>> > > > > > > >> idea to use the change-forwarding mechanism to > > > > > >>> > > > > > > >> check > > > > for > > > > > >>> no-ops even > > > > > >>> > > > > > on > > > > > >>> > > > > > > >> stateless operations is pretty interesting. > > > > Specifically, > > > > > >>> this would > > > > > >>> > > > > > > >> _really_ > > > > > >>> > > > > > > >> let you pare down useless updates by using > > > > > >>> > > > > > > >> mapValues > > > > to > > > > > >>> strip down > > > > > >>> > > > > > > records > > > > > >>> > > > > > > >> only > > > > > >>> > > > > > > >> to what you really need. However, the dependence on > > > > the > > > > > >>> > > > > > implementation of > > > > > >>> > > > > > > >> equals() is troubling. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> It might make sense to table this idea, as well as > > > > > >>> > > > > > > >> my > > > > > >>> complicated > > > > > >>> > > > > > no-op > > > > > >>> > > > > > > >> detection algorithm, and initially propose just a > > > > > >>> nonconfigurable > > > > > >>> > > > > > feature > > > > > >>> > > > > > > >> to > > > > > >>> > > > > > > >> check "old" and "new" results for binary equality > > > > before > > > > > >>> forwarding. > > > > > >>> > > > > > > I.e., > > > > > >>> > > > > > > >> if > > > > > >>> > > > > > > >> any operation determines that the old and new > > > > > >>> > > > > > > >> results > > > > are > > > > > >>> > > > > > > >> binary-identical, we > > > > > >>> > > > > > > >> would not forward. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> I'll admit that this doesn't serve Tommy's use case > > > > very > > > > > >>> well, but it > > > > > >>> > > > > > > >> might be > > > > > >>> > > > > > > >> better to take baby steps with an optimization like > > > > this > > > > > >>> and not risk > > > > > >>> > > > > > > >> over-reaching in a way that actually harms > > > > performance or > > > > > >>> > > > > > correctness. We > > > > > >>> > > > > > > >> could > > > > > >>> > > > > > > >> always expand the feature to use equals() or some > > > > kind of > > > > > >>> > > > > > ChangeDetector > > > > > >>> > > > > > > >> later > > > > > >>> > > > > > > >> on, in a more focused discussion. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> Regarding metrics or debug logs, I guess I don't > > > > > >>> > > > > > > >> feel > > > > > >>> strongly, but it > > > > > >>> > > > > > > >> feels > > > > > >>> > > > > > > >> like two things will happen that make it nicer to > > > > > >>> > > > > > > >> add > > > > > >>> them: > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> 1. This feature is going to surprise/annoy > > > > > >>> > > > > > > >> _somebody_, > > > > > >>> and it would be > > > > > >>> > > > > > > >> nice to > > > > > >>> > > > > > > >> be able to definitively say the reason that updates > > > > are > > > > > >>> dropped is > > > > > >>> > > > > > that > > > > > >>> > > > > > > >> they > > > > > >>> > > > > > > >> were no-ops. The easiest smoking gun is if there > > > > > >>> > > > > > > >> are > > > > > >>> debug-logs that > > > > > >>> > > > > > > can be > > > > > >>> > > > > > > >> enabled. This person might just be looking at the > > > > > >>> dashboards, > > > > > >>> > > > > > > wondering why > > > > > >>> > > > > > > >> there are 100K updates per second going into their > > > > app, > > > > > >>> but only 1K > > > > > >>> > > > > > > >> results per > > > > > >>> > > > > > > >> second coming out. Having the metric there makes > > > > > >>> > > > > > > >> the > > > > > >>> accounting > > > > > >>> > > > > > easier. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> 2. Somebody is going to struggle with high-volume > > > > > >>> updates, and it > > > > > >>> > > > > > > would be > > > > > >>> > > > > > > >> nice > > > > > >>> > > > > > > >> for them to know that this feature is saving them > > > > > >>> X-thousand updates > > > > > >>> > > > > > per > > > > > >>> > > > > > > >> second, > > > > > >>> > > > > > > >> etc. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> What does everyone think about this? Note, as I > > > > > >>> > > > > > > >> read > > > > it, > > > > > >>> what I've > > > > > >>> > > > > > said > > > > > >>> > > > > > > >> above is > > > > > >>> > > > > > > >> already reflected in the text of the KIP. > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> Thanks, > > > > > >>> > > > > > > >> -John > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > >> On Tue, Feb 11, 2020, at 18:27, Richard Yu wrote: > > > > > >>> > > > > > > >>> Hi all, > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > >>> Bumping this. If you feel that this KIP is not too > > > > > >>> urgent. Then let > > > > > >>> > > > > > me > > > > > >>> > > > > > > >>> know. :) > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > >>> Cheers, > > > > > >>> > > > > > > >>> Richard > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > >>> On Thu, Feb 6, 2020 at 4:55 PM Richard Yu < > > > > > >>> > > > > > yohan.richard...@gmail.com> > > > > > >>> > > > > > > >>> wrote: > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > >>>> Hi all, > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> I've had just a few thoughts regarding the > > > > forwarding > > > > > >>> of <key, > > > > > >>> > > > > > > >>>> change<old_value, new_value>>. As Matthias > > > > > >>> > > > > > > >>>> already > > > > > >>> mentioned, there > > > > > >>> > > > > > > >> are two > > > > > >>> > > > > > > >>>> separate priorities by which we can judge this > > > > > >>> > > > > > > >>>> KIP: > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> 1. A optimization perspective: In this case, the > > > > user > > > > > >>> would prefer > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>> impact of this KIP to be as minimal as possible. > > > > > >>> > > > > > > >>>> By > > > > > >>> such logic, if > > > > > >>> > > > > > > >>>> stateless operations are performed twice, that > > > > > >>> > > > > > > >>>> could > > > > > >>> prove > > > > > >>> > > > > > > >> unacceptable for > > > > > >>> > > > > > > >>>> them. (since operations can prove expensive) > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> 2. Semantics correctness perspective: Unlike the > > > > > >>> optimization > > > > > >>> > > > > > > >> approach, we > > > > > >>> > > > > > > >>>> are more concerned with all KTable operations > > > > obeying > > > > > >>> the same > > > > > >>> > > > > > emission > > > > > >>> > > > > > > >>>> policy. i.e. emit on change. In this case, a > > > > > >>> discrepancy would not > > > > > >>> > > > > > be > > > > > >>> > > > > > > >>>> tolerated, even though an extra performance cost > > > > will > > > > > >>> be incurred. > > > > > >>> > > > > > > >>>> Therefore, we will follow Matthias's approach, > > > > > >>> > > > > > > >>>> and > > > > then > > > > > >>> perform the > > > > > >>> > > > > > > >>>> operation once on the old value, and once on the > > > > new. > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> The issue here I think is more black and white > > > > > >>> > > > > > > >>>> than > > > > in > > > > > >>> between. The > > > > > >>> > > > > > > >> second > > > > > >>> > > > > > > >>>> option in particular would be favorable for users > > > > with > > > > > >>> inexpensive > > > > > >>> > > > > > > >>>> stateless operations, while for the former > > > > > >>> > > > > > > >>>> option, > > > > we > > > > > >>> are probably > > > > > >>> > > > > > > >> dealing > > > > > >>> > > > > > > >>>> with more expensive ones. So the simplest > > > > > >>> > > > > > > >>>> solution > > > > is > > > > > >>> probably to > > > > > >>> > > > > > > >> allow the > > > > > >>> > > > > > > >>>> user to choose one of the behaviors, and have a > > > > config > > > > > >>> which can > > > > > >>> > > > > > > >> switch in > > > > > >>> > > > > > > >>>> between them. > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> Its the simplest compromise I can come up with at > > > > the > > > > > >>> moment, but if > > > > > >>> > > > > > > >> you > > > > > >>> > > > > > > >>>> think you have a better plan which could better > > > > balance > > > > > >>> tradeoffs. > > > > > >>> > > > > > Then > > > > > >>> > > > > > > >>>> please let us know. :) > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> Best, > > > > > >>> > > > > > > >>>> Richard > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>> On Wed, Feb 5, 2020 at 5:12 PM John Roesler < > > > > > >>> vvcep...@apache.org> > > > > > >>> > > > > > > >> wrote: > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>>>> Hi all, > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> Thanks for the thoughtful comments! > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> I need more time to reflect on your thoughts, > > > > > >>> > > > > > > >>>>> but > > > > just > > > > > >>> wanted to > > > > > >>> > > > > > offer > > > > > >>> > > > > > > >>>>> a quick clarification about equals(). > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> I only meant that we can't be sure if a class's > > > > > >>> equals() > > > > > >>> > > > > > > >> implementation > > > > > >>> > > > > > > >>>>> returns true for two semantically identical > > > > instances. > > > > > >>> I.e., if a > > > > > >>> > > > > > > >> class > > > > > >>> > > > > > > >>>>> doesn't > > > > > >>> > > > > > > >>>>> override the default equals() implementation, > > > > > >>> > > > > > > >>>>> then > > > > we > > > > > >>> would see > > > > > >>> > > > > > > >> behavior > > > > > >>> > > > > > > >>>>> like: > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> new MyPair("A", 1).equals(new MyPair("A", 1)) > > > > returns > > > > > >>> false > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> In that case, I would still like to catch no-op > > > > > >>> updates by > > > > > >>> > > > > > comparing > > > > > >>> > > > > > > >> the > > > > > >>> > > > > > > >>>>> serialized form of the records when we happen to > > > > have > > > > > >>> it serialized > > > > > >>> > > > > > > >> anyway > > > > > >>> > > > > > > >>>>> (such as when the operation is stateful, or when > > > > we're > > > > > >>> sending to a > > > > > >>> > > > > > > >>>>> repartition topic and we have both the "new" and > > > > "old" > > > > > >>> value from > > > > > >>> > > > > > > >>>>> upstream). > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> I didn't mean to suggest we'd try to use > > > > reflection to > > > > > >>> detect > > > > > >>> > > > > > whether > > > > > >>> > > > > > > >>>>> equals > > > > > >>> > > > > > > >>>>> is implemented, although that is a neat trick. I > > > > was > > > > > >>> thinking more > > > > > >>> > > > > > of > > > > > >>> > > > > > > >> a > > > > > >>> > > > > > > >>>>> belt-and-suspenders algorithm where we do the > > > > > >>> > > > > > > >>>>> check > > > > > >>> for no-ops > > > > > >>> > > > > > based > > > > > >>> > > > > > > >> on > > > > > >>> > > > > > > >>>>> equals() and then _also_ check the serialized > > > > > >>> > > > > > > >>>>> bytes > > > > > >>> for equality. > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> Thanks, > > > > > >>> > > > > > > >>>>> -John > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>> On Wed, Feb 5, 2020, at 15:31, Ted Yu wrote: > > > > > >>> > > > > > > >>>>>> Thanks for the comments, Matthias. > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>>> w.r.t. requirement of an `equals()` > > > > implementation, > > > > > >>> each template > > > > > >>> > > > > > > >> type > > > > > >>> > > > > > > >>>>>> would have an equals() method. We can use the > > > > > >>> following code to > > > > > >>> > > > > > know > > > > > >>> > > > > > > >>>>>> whether it is provided by JVM or provided by > > > > > >>> > > > > > > >>>>>> user. > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>>> boolean customEquals = false; > > > > > >>> > > > > > > >>>>>> try { > > > > > >>> > > > > > > >>>>>> Class cls = > > > > value.getClass().getMethod("equals", > > > > > >>> > > > > > > >>>>>> Object.class).getDeclaringClass(); > > > > > >>> > > > > > > >>>>>> if (!Object.class.equals(cls)) { > > > > > >>> > > > > > > >>>>>> customEquals = true; > > > > > >>> > > > > > > >>>>>> } > > > > > >>> > > > > > > >>>>>> } catch (NoSuchMethodException nsme) { > > > > > >>> > > > > > > >>>>>> // equals is always defined, this wouldn't > > > > > >>> > > > > > > >>>>>> hit > > > > > >>> > > > > > > >>>>>> } > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>>> The next question is: what if the user doesn't > > > > > >>> provide equals() > > > > > >>> > > > > > > >> method ? > > > > > >>> > > > > > > >>>>>> Would we automatically fall back to > > > > emit-on-update ? > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>>> Cheers > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>>> On Tue, Feb 4, 2020 at 1:37 PM Matthias J. Sax > > > > > >>> > > > > > > >>>>>> < > > > > > >>> mj...@apache.org> > > > > > >>> > > > > > > >>>>> wrote: > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > > First a high level comment: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Overall, I would like to make one step back, and > > > > > >>> > > > > > > > make > > > > sure > > > > > >>> we are > > > > > >>> > > > > > > > discussion on the same level. Originally, I > > > > > >>> > > > > > > > understood > > > > > >>> this KIP > > > > > >>> > > > > > > >>> as a > > > > > >>> > > > > > > > proposed change of _semantics_, however, given the > > > > latest > > > > > >>> > > > > > > >>> discussion > > > > > >>> > > > > > > > it seems it's actually not -- it's more an > > > > _optimization_ > > > > > >>> > > > > > > >>> proposal. > > > > > >>> > > > > > > > Hence, we only need to make sure that this > > > > > >>> > > > > > > > optimization > > > > > >>> does not > > > > > >>> > > > > > > >>> break > > > > > >>> > > > > > > > existing semantics. It this the right way to think > > > > about > > > > > >>> it? > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > If yes, than it might actually be ok to have > > > > > >>> > > > > > > > different > > > > > >>> behavior > > > > > >>> > > > > > > > depending if there is a materialized KTable or not. > > > > > >>> > > > > > > > So > > > > > >>> far, we > > > > > >>> > > > > > > >>> never > > > > > >>> > > > > > > > defined a public contract about our emit strategy > > > > > >>> > > > > > > > and > > > > it > > > > > >>> seems > > > > > >>> > > > > > > >>> this > > > > > >>> > > > > > > > KIP does not define one either. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Hence, I don't have as strong of an opinion about > > > > sending > > > > > >>> > > > > > > >>> oldValues > > > > > >>> > > > > > > > for example any longer. I guess the question is > > > > > >>> > > > > > > > really, > > > > > >>> what can > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > > implement in a reasonable way. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Other comments: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > @Richard: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Can you please add the KIP to the KIP overview > > > > > >>> > > > > > > > table: > > > > It's > > > > > >>> missing > > > > > >>> > > > > > > > ( > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > > > > > >>> > > > > https://cwiki.apache.org/confluence/display/KAFKA/Kafka+Improvement+Pro > > > > > >>> > > > > > > > posals). > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > @Bruno: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > You mentioned caching. I think it's irrelevant > > > > > >>> (orthogonal) and > > > > > >>> > > > > > > >>> we can > > > > > >>> > > > > > > > discuss this KIP without considering it. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > @John: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>>>>> Even in the source table, we forward the > > > > updated > > > > > >>> record with > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>> higher of the two timestamps. So the > > > > > >>> > > > > > > >>>>>>>>> example is > > > > > >>> more like: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > That is not correct. Currently, we forward with the > > > > smaller > > > > > >>> > > > > > > > out-of-order timestamp (changing the timestamp would > > > > > >>> corrupt the > > > > > >>> > > > > > > >>> data > > > > > >>> > > > > > > > -- we don't know, because we don't check, if the > > > > > >>> > > > > > > > value > > > > is > > > > > >>> the > > > > > >>> > > > > > > >>> same > > > > > >>> > > > > > > >>>>>> or > > > > > >>> > > > > > > > a different one, hence, we must emit the > > > > > >>> > > > > > > > out-of-order > > > > > >>> record > > > > > >>> > > > > > > >>> as-is). > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > If we start to do emit-on-change, we also need to > > > > > >>> > > > > > > > emit > > > > a > > > > > >>> new > > > > > >>> > > > > > > >>> record if > > > > > >>> > > > > > > > the timestamp changes due to out-of-order data, > > > > > >>> > > > > > > > hence, > > > > we > > > > > >>> would > > > > > >>> > > > > > > >>> still > > > > > >>> > > > > > > > need to emit <K,V,T1> because that give us correct > > > > > >>> semantics: > > > > > >>> > > > > > > >>> assume > > > > > >>> > > > > > > > you have a filter() and afterward use the filter > > > > KTable in > > > > > >>> a > > > > > >>> > > > > > > > stream-table join -- the lower T1 timestamp must be > > > > > >>> propagated to > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > > filtered KTable to ensure that that the stream-table > > > > join > > > > > >>> compute > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > > correct result. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Your point about requiring an `equals()` > > > > implementation is > > > > > >>> > > > > > > >>> actually a > > > > > >>> > > > > > > > quite interesting one and boils down to my statement > > > > from > > > > > >>> above > > > > > >>> > > > > > > >>> about > > > > > >>> > > > > > > > "what can we actually implement". What I don't > > > > understand > > > > > >>> is: > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>>>>> This way, we still don't have to rely on the > > > > > >>> existence of an > > > > > >>> > > > > > > >>>>>>>>> equals() method, but if it is there, we can > > > > > >>> benefit from it. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > Your bullet point (2) says it uses `equals()` -- > > > > hence, it > > > > > >>> seems > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > > actually to rely on it? Also, how can we detect if > > > > there > > > > > >>> is an > > > > > >>> > > > > > > > `equals()` method to do the comparison? Would be > > > > > >>> > > > > > > > fail > > > > if > > > > > >>> we don't > > > > > >>> > > > > > > >>> have > > > > > >>> > > > > > > > `equals()` nor corresponding serializes to do the > > > > > >>> comparison? > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>>>>> Wow, really good catch! Yes, we absolutely > > > > > >>> > > > > > > >>>>>>>>> need > > > > > >>> metrics and > > > > > >>> > > > > > > >>> logs if > > > > > >>> > > > > > > >>>>>>>>> we're going to drop any records. And, yes, > > > > > >>> > > > > > > >>>>>>>>> we > > > > > >>> should propose > > > > > >>> > > > > > > >>>>>>>>> metrics and logs that are similar to the > > > > existing > > > > > >>> ones when we > > > > > >>> > > > > > > >>> drop > > > > > >>> > > > > > > >>>>>>>>> records for other reasons. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > I am not sure about this point. In fact, we have > > > > already > > > > > >>> some > > > > > >>> > > > > > > >>> no-ops > > > > > >>> > > > > > > > in Kafka Streams in our join-operators and don't > > > > > >>> > > > > > > > report > > > > > >>> any of > > > > > >>> > > > > > > >>> those > > > > > >>> > > > > > > > either. Emit-on-change is operator semantics and I > > > > don't > > > > > >>> see why > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > > would need to have a metric for it? It seems to be > > > > quite > > > > > >>> different > > > > > >>> > > > > > > > compared to dropping late or malformed records. > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > -Matthias > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > On 2/4/20 7:13 AM, Thomas Becker wrote: > > > > > >>> > > > > > > >>>>>>>>> Thanks John for your thoughtful reply. Some > > > > > >>> comments inline. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> On Mon, 2020-02-03 at 11:51 -0600, John > > > > > >>> > > > > > > >>>>>>>>> Roesler > > > > > >>> wrote: > > > > > >>> > > > > > > >>>>>>>>>> [EXTERNAL EMAIL] Attention: This email was > > > > sent > > > > > >>> from outside > > > > > >>> > > > > > > >>>>>>>>>> TiVo. DO NOT CLICK any links or attachments > > > > > >>> unless you > > > > > >>> > > > > > expected > > > > > >>> > > > > > > >>>>>>>>>> them. ________________________________ > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Hi Tommy, > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Thanks for the context. I can see the > > > > attraction > > > > > >>> of > > > > > >>> > > > > > considering > > > > > >>> > > > > > > >>>>>>>>>> these use cases together. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> To answer your question, if a part of the > > > > record > > > > > >>> is not > > > > > >>> > > > > > > >>> relevant > > > > > >>> > > > > > > >>>>>>>>>> to downstream consumers, I was thinking you > > > > could > > > > > >>> just use a > > > > > >>> > > > > > > >>>>>>>>>> mapValue to remove it. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> E.g., suppose you wanted to do a join > > > > > >>> > > > > > > >>>>>>>>>> between > > > > two > > > > > >>> tables. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> employeeInfo.join( employeePayroll, (info, > > > > > >>> payroll) -> new > > > > > >>> > > > > > > >>>>>>>>>> Result(info.name(), payroll.salary()) ) > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> We only care about one attribute from the > > > > > >>> > > > > > > >>>>>>>>>> Info > > > > > >>> table (name), > > > > > >>> > > > > > > >>> and > > > > > >>> > > > > > > >>>>>>>>>> one from the Payroll table (salary), and > > > > > >>> > > > > > > >>>>>>>>>> these > > > > > >>> attributes > > > > > >>> > > > > > > >>> change > > > > > >>> > > > > > > >>>>>>>>>> rarely. On the other hand, there might be > > > > > >>> > > > > > > >>>>>>>>>> many > > > > > >>> other > > > > > >>> > > > > > attributes > > > > > >>> > > > > > > >>>>>>>>>> that change frequently of these tables. We > > > > > >>> > > > > > > >>>>>>>>>> can > > > > > >>> avoid > > > > > >>> > > > > > triggering > > > > > >>> > > > > > > >>>>>>>>>> the join unnecessarily by mapping the input > > > > > >>> tables to drop the > > > > > >>> > > > > > > >>>>>>>>>> unnecessary information before the join: > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> names = employeeInfo.mapValues(info -> > > > > info.name()) > > > > > >>> salaries > > > > > >>> > > > > > = > > > > > >>> > > > > > > >>>>>>>>>> employeePayroll.mapValues(payroll -> > > > > > >>> payroll.salary()) > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> names.join( salaries, (name, salary) -> new > > > > > >>> Result(name, > > > > > >>> > > > > > > >>> salary) > > > > > >>> > > > > > > >>>>>>>>>> ) > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> Ahh yes I see. This works, but in the case > > > > where > > > > > >>> you're using > > > > > >>> > > > > > > >>>>>>>>> schemas as we are (e.g. Avro), it seems like > > > > this > > > > > >>> approach > > > > > >>> > > > > > could > > > > > >>> > > > > > > >>>>>>>>> lead to a proliferation of "skinny" record > > > > types > > > > > >>> that just drop > > > > > >>> > > > > > > >>>>>>>>> various fields. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Especially if we take Matthias's idea to > > > > > >>> > > > > > > >>>>>>>>>> drop > > > > > >>> non-changes even > > > > > >>> > > > > > > >>>>>>>>>> for stateless operations, this would be > > > > > >>> > > > > > > >>>>>>>>>> quite > > > > > >>> efficient and is > > > > > >>> > > > > > > >>>>>>>>>> also a very straightforward optimization to > > > > > >>> understand once > > > > > >>> > > > > > you > > > > > >>> > > > > > > >>>>>>>>>> know that Streams provides emit-on-change. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> From the context that you provided, it > > > > > >>> > > > > > > >>>>>>>>>> seems > > > > like > > > > > >>> a slightly > > > > > >>> > > > > > > >>>>>>>>>> different situation, though. Reading > > > > > >>> > > > > > > >>>>>>>>>> between > > > > the > > > > > >>> lines a > > > > > >>> > > > > > > >>> little, > > > > > >>> > > > > > > >>>>>>>>>> it sounds like: in contrast to the example > > > > above, > > > > > >>> in which we > > > > > >>> > > > > > > >>> are > > > > > >>> > > > > > > >>>>>>>>>> filtering out extra _data_, you have some > > > > extra > > > > > >>> _metadata_ > > > > > >>> > > > > > that > > > > > >>> > > > > > > >>>>>>>>>> you still wish to pass down with the data > > > > > >>> > > > > > > >>>>>>>>>> when > > > > > >>> there is a > > > > > >>> > > > > > > >>> "real" > > > > > >>> > > > > > > >>>>>>>>>> update, but you don't want the metadata > > > > itself to > > > > > >>> cause an > > > > > >>> > > > > > > >>>>>>>>>> update. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> Despite my lack of clarity, yes you've got > > > > > >>> > > > > > > >>>>>>>>> it > > > > > >>> right ;) This > > > > > >>> > > > > > > >>>>>>>>> particular processor is the first stop for > > > > > >>> > > > > > > >>>>>>>>> this > > > > > >>> data after > > > > > >>> > > > > > > >>> coming > > > > > >>> > > > > > > >>>>>>>>> in from external users, who often simply > > > > > >>> > > > > > > >>>>>>>>> post > > > > the > > > > > >>> same content > > > > > >>> > > > > > > >>> each > > > > > >>> > > > > > > >>>>>>>>> time and we're trying to shield downstream > > > > > >>> consumers from > > > > > >>> > > > > > > >>>>>>>>> unnecessary churn. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> It does seem handy to be able to plug in a > > > > custom > > > > > >>> > > > > > > >>> ChangeDetector > > > > > >>> > > > > > > >>>>>>>>>> for this purpose, but I worry about the API > > > > > >>> complexity. Maybe > > > > > >>> > > > > > > >>> you > > > > > >>> > > > > > > >>>>>>>>>> can help think though how to provide the > > > > > >>> > > > > > > >>>>>>>>>> same > > > > > >>> benefit while > > > > > >>> > > > > > > >>>>>>>>>> limiting user-facing complexity. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Here's some extra context to consider: > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> We currently don't make any extra > > > > > >>> > > > > > > >>>>>>>>>> requirements > > > > > >>> about the > > > > > >>> > > > > > nature > > > > > >>> > > > > > > >>>>>>>>>> of data that you can use in Streams. For > > > > example, > > > > > >>> you don't > > > > > >>> > > > > > > >>> have > > > > > >>> > > > > > > >>>>>>>>>> to implement hashCode and equals, or > > > > compareTo, > > > > > >>> etc. With the > > > > > >>> > > > > > > >>>>>>>>>> current proposal, we can do an airtight > > > > > >>> comparison based only > > > > > >>> > > > > > > >>> on > > > > > >>> > > > > > > >>>>>>>>>> the serialized form of the values, and we > > > > > >>> actually don't have > > > > > >>> > > > > > > >>> to > > > > > >>> > > > > > > >>>>>>>>>> deserialize the "prior" value at all for a > > > > large > > > > > >>> number of > > > > > >>> > > > > > > >>>>>>>>>> operations. Admitedly, if we extend the > > > > proposal > > > > > >>> to include > > > > > >>> > > > > > > >>> no-op > > > > > >>> > > > > > > >>>>>>>>>> detection for stateless operations, we'd > > > > probably > > > > > >>> need to rely > > > > > >>> > > > > > > >>> on > > > > > >>> > > > > > > >>>>>>>>>> equals() for no-op checking, otherwise we'd > > > > wind > > > > > >>> up requiring > > > > > >>> > > > > > > >>>>>>>>>> serdes for stateless operations as well. > > > > > >>> Actually, I'd > > > > > >>> > > > > > probably > > > > > >>> > > > > > > >>>>>>>>>> argue for doing exactly that: > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> 1. In stateful operations, drop if the > > > > serialized > > > > > >>> byte[]s are > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> same. After deserializing, also drop if the > > > > > >>> objects are equal > > > > > >>> > > > > > > >>>>>>>>>> according to Object#equals(). > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> 2. In stateless operations, compare the > > > > > >>> > > > > > > >>>>>>>>>> "new" > > > > and > > > > > >>> "old" values > > > > > >>> > > > > > > >>>>>>>>>> (if "old" is available) based on > > > > Object#equals(). > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> 3. As a final optimization, after > > > > > >>> > > > > > > >>>>>>>>>> serializing > > > > and > > > > > >>> before > > > > > >>> > > > > > > >>> sending > > > > > >>> > > > > > > >>>>>>>>>> repartition records, compare the serialized > > > > data > > > > > >>> and drop > > > > > >>> > > > > > > >>>>>>>>>> no-ops. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> This way, we still don't have to rely on > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> existence of an > > > > > >>> > > > > > > >>>>>>>>>> equals() method, but if it is there, we can > > > > > >>> benefit from it. > > > > > >>> > > > > > > >>>>>>>>>> Also, we don't require a serde in any new > > > > > >>> situations, but we > > > > > >>> > > > > > > >>> can > > > > > >>> > > > > > > >>>>>>>>>> still leverage it when it is available. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> For clarity, in my example above, even if > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> employeeInfo and > > > > > >>> > > > > > > >>>>>>>>>> employeePayroll and Result records all have > > > > > >>> serdes, we need > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> "name" field (presumably String) and the > > > > "salary" > > > > > >>> field > > > > > >>> > > > > > > >>>>>>>>>> (presumable a Double) to have serdes as > > > > > >>> > > > > > > >>>>>>>>>> well > > > > in > > > > > >>> the naive > > > > > >>> > > > > > > >>>>>>>>>> implementation. But if we can leverage > > > > equals(), > > > > > >>> then the > > > > > >>> > > > > > > >>> "right > > > > > >>> > > > > > > >>>>>>>>>> thing" happens automatically. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> I still don't totally follow why the > > > > > >>> > > > > > > >>>>>>>>> individual > > > > > >>> components > > > > > >>> > > > > > > >>> (name, > > > > > >>> > > > > > > >>>>>>>>> salary) would have to have serdes here. If > > > > Result > > > > > >>> has one, we > > > > > >>> > > > > > > >>>>>>>>> compare bytes, and if Result additionally > > > > > >>> > > > > > > >>>>>>>>> has > > > > an > > > > > >>> equals() > > > > > >>> > > > > > method > > > > > >>> > > > > > > >>>>>>>>> (which presumably includes equals > > > > > >>> > > > > > > >>>>>>>>> comparisons > > > > on > > > > > >>> the > > > > > >>> > > > > > constituent > > > > > >>> > > > > > > >>>>>>>>> fields), have we not covered our bases? > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> This dovetails in with my primary UX > > > > > >>> > > > > > > >>>>>>>>>> concern; > > > > > >>> where would the > > > > > >>> > > > > > > >>>>>>>>>> ChangeDetector actually be registered? > > > > > >>> > > > > > > >>>>>>>>>> None of > > > > > >>> the operators > > > > > >>> > > > > > in > > > > > >>> > > > > > > >>>>>>>>>> my example have names or topics or any > > > > > >>> > > > > > > >>>>>>>>>> other > > > > > >>> identifiable > > > > > >>> > > > > > > >>>>>>>>>> characteristic that could be passed to a > > > > > >>> ChangeDetector class > > > > > >>> > > > > > > >>>>>>>>>> registered via config. You could say that > > > > > >>> > > > > > > >>>>>>>>>> we > > > > make > > > > > >>> > > > > > > >>> ChangeDetector > > > > > >>> > > > > > > >>>>>>>>>> an optional parameter to every operation in > > > > > >>> Streams, but this > > > > > >>> > > > > > > >>>>>>>>>> seems to carry quite a bit of mental burden > > > > with > > > > > >>> it. People > > > > > >>> > > > > > > >>> will > > > > > >>> > > > > > > >>>>>>>>>> wonder what it's for and whether or not > > > > > >>> > > > > > > >>>>>>>>>> they > > > > > >>> should be using > > > > > >>> > > > > > > >>> it. > > > > > >>> > > > > > > >>>>>>>>>> There would almost certainly be a > > > > misconception > > > > > >>> that it's > > > > > >>> > > > > > > >>>>>>>>>> preferable to implement it always, which > > > > would be > > > > > >>> unfortunate. > > > > > >>> > > > > > > >>>>>>>>>> Plus, to actually implment metadata flowing > > > > > >>> through the > > > > > >>> > > > > > > >>> topology > > > > > >>> > > > > > > >>>>>>>>>> as in your use case, you'd have to do two > > > > things: > > > > > >>> 1. make sure > > > > > >>> > > > > > > >>>>>>>>>> that all operations actually preserve the > > > > > >>> metadata alongside > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> data (e.g., don't accidentally add a > > > > > >>> > > > > > > >>>>>>>>>> mapValues > > > > > >>> like I did, or > > > > > >>> > > > > > > >>> you > > > > > >>> > > > > > > >>>>>>>>>> drop the metadata). 2. implement a > > > > ChangeDetector > > > > > >>> for every > > > > > >>> > > > > > > >>>>>>>>>> single operation in the topology, or you > > > > > >>> > > > > > > >>>>>>>>>> don't > > > > > >>> get the benefit > > > > > >>> > > > > > > >>> of > > > > > >>> > > > > > > >>>>>>>>>> dropping non-changes internally 2b. > > > > > >>> Alternatively, you could > > > > > >>> > > > > > > >>> just > > > > > >>> > > > > > > >>>>>>>>>> add the ChangeDetector to one operation > > > > > >>> > > > > > > >>>>>>>>>> toward > > > > > >>> the end of the > > > > > >>> > > > > > > >>>>>>>>>> topology. This would not drop redundant > > > > > >>> computation > > > > > >>> > > > > > internally, > > > > > >>> > > > > > > >>>>>>>>>> but only drop redundant _outputs_. But > > > > > >>> > > > > > > >>>>>>>>>> this is > > > > > >>> just about the > > > > > >>> > > > > > > >>>>>>>>>> same as your current solution. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> I definitely see your point regarding > > > > > >>> configuration. I was > > > > > >>> > > > > > > >>>>>>>>> originally thinking about this when the > > > > > >>> deduplication was going > > > > > >>> > > > > > > >>> to > > > > > >>> > > > > > > >>>>>>>>> be opt-in, and it seemed very natural to say > > > > > >>> something like: > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> employeeInfo.join(employeePayroll, (info, > > > > payroll) > > > > > >>> -> new > > > > > >>> > > > > > > >>>>>>>>> Result(info.name(), payroll.salary())) > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> .suppress(duplicatesAccordingTo(someChangeDetector)) > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> Alternatively you can imagine a similar > > > > > >>> > > > > > > >>>>>>>>> method > > > > > >>> being on > > > > > >>> > > > > > > >>>>>>>>> Materialized, though obviously this makes > > > > > >>> > > > > > > >>>>>>>>> less > > > > > >>> sense if we > > > > > >>> > > > > > don't > > > > > >>> > > > > > > >>>>>>>>> want to require materialization. If we're > > > > > >>> > > > > > > >>>>>>>>> now > > > > > >>> talking about > > > > > >>> > > > > > > >>>>>>>>> changing the default behavior and not having > > > > any > > > > > >>> configuration > > > > > >>> > > > > > > >>>>>>>>> options, it's harder to find a place for > > > > > >>> > > > > > > >>>>>>>>> this. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> A final thought; if it really is a metadata > > > > > >>> question, can we > > > > > >>> > > > > > > >>> just > > > > > >>> > > > > > > >>>>>>>>>> plan to finish up the support for headers > > > > > >>> > > > > > > >>>>>>>>>> in > > > > > >>> Streams? I.e., > > > > > >>> > > > > > > >>> give > > > > > >>> > > > > > > >>>>>>>>>> you a way to control the way that headers > > > > > >>> > > > > > > >>>>>>>>>> flow > > > > > >>> through the > > > > > >>> > > > > > > >>>>>>>>>> topology? Then, we could treat headers the > > > > same > > > > > >>> way we treat > > > > > >>> > > > > > > >>>>>>>>>> timestamps in the no-op checking... We > > > > completely > > > > > >>> ignore them > > > > > >>> > > > > > > >>>>>>>>>> for the sake of comparison. Thus, neither > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> timestamp nor > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> headers would get updated in internal state > > > > or in > > > > > >>> downstream > > > > > >>> > > > > > > >>>>>>>>>> views as long as the value itself doesn't > > > > change. > > > > > >>> This seems > > > > > >>> > > > > > to > > > > > >>> > > > > > > >>>>>>>>>> give us a way to support your use case > > > > > >>> > > > > > > >>>>>>>>>> without > > > > > >>> adding to the > > > > > >>> > > > > > > >>>>>>>>>> mental overhead of using Streams for simple > > > > > >>> things. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> Agree headers could be a decent fit for this > > > > > >>> particular case > > > > > >>> > > > > > > >>>>>>>>> because it's mostly metadata, though to be > > > > honest > > > > > >>> we haven't > > > > > >>> > > > > > > >>> looked > > > > > >>> > > > > > > >>>>>>>>> at headers much (mostly because, and to your > > > > > >>> point, support > > > > > >>> > > > > > > >>> seems > > > > > >>> > > > > > > >>>>>>>>> to be lacking). I feel like there would be > > > > other > > > > > >>> cases where > > > > > >>> > > > > > > >>> this > > > > > >>> > > > > > > >>>>>>>>> feature could be valuable, but I admit I > > > > > >>> > > > > > > >>>>>>>>> can't > > > > > >>> come up with > > > > > >>> > > > > > > >>>>>>>>> anything right this second. Perhaps > > > > > >>> > > > > > > >>>>>>>>> yuzhihong > > > > had > > > > > >>> an example in > > > > > >>> > > > > > > >>>>>>>>> mind? > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> I.e., simple things should be easy, and > > > > complex > > > > > >>> things should > > > > > >>> > > > > > > >>> be > > > > > >>> > > > > > > >>>>>>>>>> possible. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> What are your thoughts? Thanks, -John > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Mon, Feb 3, 2020, at 07:19, Thomas > > > > > >>> > > > > > > >>>>>>>>>> Becker > > > > > >>> wrote: > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Hi John, Can you describe how you'd use > > > > > >>> filtering/mapping to > > > > > >>> > > > > > > >>>>>>>>>> deduplicate records? To give some > > > > > >>> > > > > > > >>>>>>>>>> background > > > > on > > > > > >>> my suggestion > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > >>>>>>>>>> currently have a small stream processor > > > > > >>> > > > > > > >>>>>>>>>> that > > > > > >>> exists solely to > > > > > >>> > > > > > > >>>>>>>>>> deduplicate, which we do using a process > > > > > >>> > > > > > > >>>>>>>>>> that > > > > I > > > > > >>> assume would > > > > > >>> > > > > > be > > > > > >>> > > > > > > >>>>>>>>>> similar to what would be done here (with a > > > > store > > > > > >>> of keys and > > > > > >>> > > > > > > >>> hash > > > > > >>> > > > > > > >>>>>>>>>> values). But the records we are > > > > > >>> > > > > > > >>>>>>>>>> deduplicating > > > > > >>> have some > > > > > >>> > > > > > > >>> metadata > > > > > >>> > > > > > > >>>>>>>>>> fields (such as timestamps of when the > > > > > >>> > > > > > > >>>>>>>>>> record > > > > was > > > > > >>> posted) that > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > >>>>>>>>>> don't consider semantically meaningful for > > > > > >>> downstream > > > > > >>> > > > > > > >>> consumers, > > > > > >>> > > > > > > >>>>>>>>>> and therefore we also suppress updates that > > > > only > > > > > >>> touch those > > > > > >>> > > > > > > >>>>>>>>>> fields. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> -Tommy > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Fri, 2020-01-31 at 19:30 -0600, John > > > > Roesler > > > > > >>> wrote: > > > > > >>> > > > > > > >>> [EXTERNAL > > > > > >>> > > > > > > >>>>>>>>>> EMAIL] Attention: This email was sent from > > > > > >>> outside TiVo. DO > > > > > >>> > > > > > NOT > > > > > >>> > > > > > > >>>>>>>>>> CLICK any links or attachments unless you > > > > > >>> expected them. > > > > > >>> > > > > > > >>>>>>>>>> ________________________________ > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Hi Thomas and yuzhihong, That’s an > > > > > >>> > > > > > > >>>>>>>>>> interesting > > > > > >>> idea. Can you > > > > > >>> > > > > > > >>> help > > > > > >>> > > > > > > >>>>>>>>>> think of a use case that isn’t also served > > > > > >>> > > > > > > >>>>>>>>>> by > > > > > >>> filtering or > > > > > >>> > > > > > > >>>>>>>>>> mapping beforehand? Thanks for helping to > > > > design > > > > > >>> this feature! > > > > > >>> > > > > > > >>>>>>>>>> -John On Fri, Jan 31, 2020, at 18:56, > > > > > >>> yuzhih...@gmail.com > > > > > >>> > > > > > > >>>>>>>>>> <mailto:yuzhih...@gmail.com> wrote: I think > > > > this > > > > > >>> is good > > > > > >>> > > > > > > >>> idea. On > > > > > >>> > > > > > > >>>>>>>>>> Jan 31, 2020, at 4:49 PM, Thomas Becker < > > > > > >>> > > > > > > >>> thomas.bec...@tivo.com > > > > > >>> > > > > > > >>>>>>>>>> <mailto:thomas.bec...@tivo.com>> wrote: > > > > > >>> > > > > > > >>>>>>>>>> How > > > > do > > > > > >>> folks feel > > > > > >>> > > > > > > >>> about > > > > > >>> > > > > > > >>>>>>>>>> allowing the mechanism by which no-ops are > > > > > >>> detected to be > > > > > >>> > > > > > > >>>>>>>>>> pluggable? Meaning use something like a > > > > > >>> > > > > > > >>>>>>>>>> hash > > > > by > > > > > >>> default, but > > > > > >>> > > > > > > >>> you > > > > > >>> > > > > > > >>>>>>>>>> could optionally provide an implementation > > > > > >>> > > > > > > >>>>>>>>>> of > > > > > >>> something to use > > > > > >>> > > > > > > >>>>>>>>>> instead, like a ChangeDetector. This could > > > > > >>> > > > > > > >>>>>>>>>> be > > > > > >>> useful for > > > > > >>> > > > > > > >>> example > > > > > >>> > > > > > > >>>>>>>>>> to ignore changes to certain fields, which > > > > > >>> > > > > > > >>>>>>>>>> may > > > > > >>> not be relevant > > > > > >>> > > > > > > >>> to > > > > > >>> > > > > > > >>>>>>>>>> the operation being performed. > > > > > >>> > > > > > ________________________________ > > > > > >>> > > > > > > >>>>>>>>>> From: John Roesler <vvcep...@apache.org > > > > > >>> > > > > > > >>>>>>>>>> <mailto:vvcep...@apache.org>> Sent: Friday, > > > > > >>> January 31, 2020 > > > > > >>> > > > > > > >>> 4:51 > > > > > >>> > > > > > > >>>>>>>>>> PM To: dev@kafka.apache.org <mailto: > > > > > >>> dev@kafka.apache.org> > > > > > >>> > > > > > > >>>>>>>>>> <dev@kafka.apache.org <mailto: > > > > > >>> dev@kafka.apache.org>> Subject: > > > > > >>> > > > > > > >>> Re: > > > > > >>> > > > > > > >>>>>>>>>> [KAFKA-557] Add emit on change support for > > > > Kafka > > > > > >>> Streams > > > > > >>> > > > > > > >>>>>>>>>> [EXTERNAL EMAIL] Attention: This email was > > > > sent > > > > > >>> from outside > > > > > >>> > > > > > > >>>>>>>>>> TiVo. DO NOT CLICK any links or attachments > > > > > >>> unless you > > > > > >>> > > > > > expected > > > > > >>> > > > > > > >>>>>>>>>> them. ________________________________ > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> Hello all, Sorry for my silence. It seems > > > > like we > > > > > >>> are getting > > > > > >>> > > > > > > >>>>>>>>>> close to consensus. Hopefully, we could > > > > > >>> > > > > > > >>>>>>>>>> move > > > > to a > > > > > >>> vote soon! > > > > > >>> > > > > > > >>> All > > > > > >>> > > > > > > >>>>>>>>>> of the reasoning from Matthias and Bruno > > > > around > > > > > >>> timestamp is > > > > > >>> > > > > > > >>>>>>>>>> compelling. I would be strongly in favor of > > > > > >>> stating a few > > > > > >>> > > > > > > >>> things > > > > > >>> > > > > > > >>>>>>>>>> very clearly in the KIP: 1. Streams will > > > > > >>> > > > > > > >>>>>>>>>> drop > > > > > >>> no-op updates > > > > > >>> > > > > > > >>> only > > > > > >>> > > > > > > >>>>>>>>>> for KTable operations. That is, we won't > > > > > >>> > > > > > > >>>>>>>>>> make > > > > any > > > > > >>> changes to > > > > > >>> > > > > > > >>>>>>>>>> KStream aggregations at the moment. It does > > > > seem > > > > > >>> like we can > > > > > >>> > > > > > > >>>>>>>>>> potentially revisit the time semantics of > > > > > >>> > > > > > > >>>>>>>>>> that > > > > > >>> operation in > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> future, but we don't need to do it now. On > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> other hand, the > > > > > >>> > > > > > > >>>>>>>>>> proposed semantics for KTable timestamps > > > > (marking > > > > > >>> the > > > > > >>> > > > > > beginning > > > > > >>> > > > > > > >>>>>>>>>> of the validity of that record) makes > > > > > >>> > > > > > > >>>>>>>>>> sense to > > > > > >>> me. 2. Streams > > > > > >>> > > > > > > >>>>>>>>>> will only drop no-op updates for _stateful_ > > > > > >>> KTable operations. > > > > > >>> > > > > > > >>> We > > > > > >>> > > > > > > >>>>>>>>>> don't want to add a hard guarantee that > > > > Streams > > > > > >>> will _never_ > > > > > >>> > > > > > > >>>>>>>>>> emit a no-op table update because it would > > > > > >>> require adding > > > > > >>> > > > > > state > > > > > >>> > > > > > > >>>>>>>>>> to otherwise stateless operations. If > > > > > >>> > > > > > > >>>>>>>>>> someone > > > > is > > > > > >>> really > > > > > >>> > > > > > > >>> concerned > > > > > >>> > > > > > > >>>>>>>>>> about a particular stateless operation > > > > producing > > > > > >>> a lot of > > > > > >>> > > > > > no-op > > > > > >>> > > > > > > >>>>>>>>>> results, all they have to do is materialize > > > > it, > > > > > >>> and Streams > > > > > >>> > > > > > > >>> would > > > > > >>> > > > > > > >>>>>>>>>> automatically drop the no-ops. > > > > > >>> > > > > > > >>>>>>>>>> Additionally, > > > > I'm > > > > > >>> +1 on not > > > > > >>> > > > > > > >>> adding > > > > > >>> > > > > > > >>>>>>>>>> an opt-out at this time. Regarding the KIP > > > > > >>> itself, I would > > > > > >>> > > > > > > >>> clean > > > > > >>> > > > > > > >>>>>>>>>> it up a bit before calling for a vote. > > > > > >>> > > > > > > >>>>>>>>>> There > > > > is a > > > > > >>> lot of > > > > > >>> > > > > > > >>>>>>>>>> "discussion"-type language there, which is > > > > very > > > > > >>> natural to > > > > > >>> > > > > > > >>> read, > > > > > >>> > > > > > > >>>>>>>>>> but makes it a bit hard to see what > > > > > >>> > > > > > > >>>>>>>>>> _exactly_ > > > > the > > > > > >>> kip is > > > > > >>> > > > > > > >>>>>>>>>> proposing. Richard, would you mind just > > > > > >>> > > > > > > >>>>>>>>>> making > > > > > >>> the "proposed > > > > > >>> > > > > > > >>>>>>>>>> behavior change" a simple and succinct > > > > > >>> > > > > > > >>>>>>>>>> list of > > > > > >>> bullet points? > > > > > >>> > > > > > > >>>>>>>>>> I.e., please drop glue phrases like "there > > > > > >>> > > > > > > >>>>>>>>>> has > > > > > >>> been some > > > > > >>> > > > > > > >>>>>>>>>> discussion" or "possibly we could do X". > > > > > >>> > > > > > > >>>>>>>>>> For > > > > the > > > > > >>> final version > > > > > >>> > > > > > > >>> of > > > > > >>> > > > > > > >>>>>>>>>> the KIP, it should just say, "Streams will > > > > > >>> > > > > > > >>>>>>>>>> do > > > > X, > > > > > >>> Streams will > > > > > >>> > > > > > > >>> do > > > > > >>> > > > > > > >>>>>>>>>> Y". Feel free to add an elaboration > > > > > >>> > > > > > > >>>>>>>>>> section to > > > > > >>> explain more > > > > > >>> > > > > > > >>> about > > > > > >>> > > > > > > >>>>>>>>>> what X and Y mean, but we don't need to > > > > > >>> > > > > > > >>>>>>>>>> talk > > > > about > > > > > >>> > > > > > > >>> possibilities > > > > > >>> > > > > > > >>>>>>>>>> or alternatives except in the "rejected > > > > > >>> alternatives" section. > > > > > >>> > > > > > > >>>>>>>>>> Accordingly, can you also move the options > > > > > >>> > > > > > > >>>>>>>>>> you > > > > > >>> presented in > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> intro to the "rejected alternatives" > > > > > >>> > > > > > > >>>>>>>>>> section > > > > and > > > > > >>> only mention > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> final proposal itself? This just really > > > > > >>> > > > > > > >>>>>>>>>> helps > > > > > >>> reviewers to > > > > > >>> > > > > > know > > > > > >>> > > > > > > >>>>>>>>>> what they are voting for, and it helps > > > > everyone > > > > > >>> after the fact > > > > > >>> > > > > > > >>>>>>>>>> when they are trying to get clarity on what > > > > > >>> exactly the > > > > > >>> > > > > > > >>> proposal > > > > > >>> > > > > > > >>>>>>>>>> is, versus all the things it could have > > > > > >>> > > > > > > >>>>>>>>>> been. > > > > > >>> Thanks, -John > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Mon, Jan 27, 2020, at 18:14, Richard Yu > > > > wrote: > > > > > >>> Hello to > > > > > >>> > > > > > all, > > > > > >>> > > > > > > >>>>>>>>>> I've finished making some initial > > > > modifications > > > > > >>> to the KIP. I > > > > > >>> > > > > > > >>>>>>>>>> have decided to keep the implementation > > > > section > > > > > >>> in the KIP for > > > > > >>> > > > > > > >>>>>>>>>> record-keeping purposes. For now, we should > > > > focus > > > > > >>> on only the > > > > > >>> > > > > > > >>>>>>>>>> proposed behavior changes instead. See if > > > > > >>> > > > > > > >>>>>>>>>> you > > > > > >>> have any > > > > > >>> > > > > > > >>> comments! > > > > > >>> > > > > > > >>>>>>>>>> Cheers, Richard On Sat, Jan 25, 2020 at > > > > > >>> > > > > > > >>>>>>>>>> 11:12 > > > > AM > > > > > >>> Richard Yu > > > > > >>> > > > > > > >>>>>>>>>> <yohan.richard...@gmail.com <mailto: > > > > > >>> > > > > > yohan.richard...@gmail.com > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>>>>>>>> wrote: Hi all, Thanks for all the > > > > > >>> > > > > > > >>>>>>>>>> discussion! > > > > > >>> @John and @Bruno > > > > > >>> > > > > > > >>> I > > > > > >>> > > > > > > >>>>>>>>>> will survey other possible systems and see > > > > what I > > > > > >>> can do. Just > > > > > >>> > > > > > > >>> a > > > > > >>> > > > > > > >>>>>>>>>> question, by systems, I suppose you would > > > > > >>> > > > > > > >>>>>>>>>> mean > > > > > >>> the pros and > > > > > >>> > > > > > > >>> cons > > > > > >>> > > > > > > >>>>>>>>>> of different reporting strategies? I'm not > > > > > >>> completely certain > > > > > >>> > > > > > > >>> on > > > > > >>> > > > > > > >>>>>>>>>> this point, so it would be great if you can > > > > > >>> clarify on that. > > > > > >>> > > > > > So > > > > > >>> > > > > > > >>>>>>>>>> here's what I got from all the discussion > > > > > >>> > > > > > > >>>>>>>>>> so > > > > far: > > > > > >>> - Since both > > > > > >>> > > > > > > >>>>>>>>>> Matthias and John seems to have come to a > > > > > >>> consensus on this, > > > > > >>> > > > > > > >>> then > > > > > >>> > > > > > > >>>>>>>>>> we will go for an all-round behavorial > > > > > >>> > > > > > > >>>>>>>>>> change > > > > for > > > > > >>> KTables. > > > > > >>> > > > > > > >>> After > > > > > >>> > > > > > > >>>>>>>>>> some thought, I decided that for now, an > > > > opt-out > > > > > >>> config will > > > > > >>> > > > > > > >>> not > > > > > >>> > > > > > > >>>>>>>>>> be added. As John have pointed out, no-op > > > > changes > > > > > >>> tend to > > > > > >>> > > > > > > >>>>>>>>>> explode further down the topology as they > > > > > >>> > > > > > > >>>>>>>>>> are > > > > > >>> forwarded to > > > > > >>> > > > > > more > > > > > >>> > > > > > > >>>>>>>>>> and more processor nodes downstream. - > > > > > >>> > > > > > > >>>>>>>>>> About > > > > > >>> using hash codes, > > > > > >>> > > > > > > >>>>>>>>>> after some explanation from John, it looks > > > > like > > > > > >>> hash codes > > > > > >>> > > > > > > >>> might > > > > > >>> > > > > > > >>>>>>>>>> not be as ideal (for implementation). For > > > > now, we > > > > > >>> will omit > > > > > >>> > > > > > > >>> that > > > > > >>> > > > > > > >>>>>>>>>> detail, and save it for the PR. - @Bruno > > > > > >>> > > > > > > >>>>>>>>>> You > > > > do > > > > > >>> have valid > > > > > >>> > > > > > > >>>>>>>>>> concerns. Though, I am not completely > > > > > >>> > > > > > > >>>>>>>>>> certain > > > > if > > > > > >>> we want to do > > > > > >>> > > > > > > >>>>>>>>>> emit-on-change only for materialized > > > > > >>> > > > > > > >>>>>>>>>> KTables. > > > > I > > > > > >>> will put it > > > > > >>> > > > > > > >>> down > > > > > >>> > > > > > > >>>>>>>>>> in the KIP regardless. I will do my best to > > > > > >>> address all points > > > > > >>> > > > > > > >>>>>>>>>> raised so far on the discussion. Hope we > > > > > >>> > > > > > > >>>>>>>>>> could > > > > > >>> keep this > > > > > >>> > > > > > going! > > > > > >>> > > > > > > >>>>>>>>>> Best, Richard On Fri, Jan 24, 2020 at 6:07 > > > > > >>> > > > > > > >>>>>>>>>> PM > > > > > >>> Bruno Cadonna > > > > > >>> > > > > > > >>>>>>>>>> <br...@confluent.io <mailto: > > > > br...@confluent.io>> > > > > > >>> wrote: Thank > > > > > >>> > > > > > > >>> you > > > > > >>> > > > > > > >>>>>>>>>> Matthias for the use cases! Looking at both > > > > use > > > > > >>> cases, I think > > > > > >>> > > > > > > >>>>>>>>>> you need to elaborate on them in the KIP, > > > > > >>> Richard. Emit from > > > > > >>> > > > > > > >>>>>>>>>> plain KTable: I agree with Matthias that > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> lower timestamp > > > > > >>> > > > > > > >>>>>>>>>> makes sense because it marks the start of > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> validity of the > > > > > >>> > > > > > > >>>>>>>>>> record. Idempotent records with a higher > > > > > >>> timestamp can be > > > > > >>> > > > > > > >>> safely > > > > > >>> > > > > > > >>>>>>>>>> ignored. A corner case that I discussed > > > > > >>> > > > > > > >>>>>>>>>> with > > > > > >>> Matthias offline > > > > > >>> > > > > > > >>> is > > > > > >>> > > > > > > >>>>>>>>>> when we do not materialize a KTable due to > > > > > >>> optimization. Then > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > >>>>>>>>>> cannot avoid the idempotent records because > > > > we do > > > > > >>> not keep the > > > > > >>> > > > > > > >>>>>>>>>> first record with the lower timestamp to > > > > compare > > > > > >>> to. Emit from > > > > > >>> > > > > > > >>>>>>>>>> KTable with aggregations: If we specify > > > > > >>> > > > > > > >>>>>>>>>> that > > > > an > > > > > >>> aggregation > > > > > >>> > > > > > > >>>>>>>>>> result should have the highest timestamp of > > > > the > > > > > >>> records that > > > > > >>> > > > > > > >>>>>>>>>> participated in the aggregation, we cannot > > > > ignore > > > > > >>> any > > > > > >>> > > > > > > >>> idempotent > > > > > >>> > > > > > > >>>>>>>>>> records. Admittedly, the result of an > > > > aggregation > > > > > >>> usually > > > > > >>> > > > > > > >>>>>>>>>> changes, but there are aggregations where > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> result may not > > > > > >>> > > > > > > >>>>>>>>>> change like min and max, or sum when the > > > > incoming > > > > > >>> records have > > > > > >>> > > > > > > >>> a > > > > > >>> > > > > > > >>>>>>>>>> value of zero. In those cases, we could > > > > benefit > > > > > >>> of the emit on > > > > > >>> > > > > > > >>>>>>>>>> change, but only if we define the semantics > > > > of the > > > > > >>> > > > > > aggregations > > > > > >>> > > > > > > >>>>>>>>>> to not use the highest timestamp of the > > > > > >>> participating records > > > > > >>> > > > > > > >>> for > > > > > >>> > > > > > > >>>>>>>>>> the result. In Kafka Streams, we do not > > > > > >>> > > > > > > >>>>>>>>>> have > > > > min, > > > > > >>> max, and sum > > > > > >>> > > > > > > >>> as > > > > > >>> > > > > > > >>>>>>>>>> explicit aggregations, but we need to > > > > > >>> > > > > > > >>>>>>>>>> provide > > > > an > > > > > >>> API to define > > > > > >>> > > > > > > >>>>>>>>>> what timestamp should be used for the > > > > > >>> > > > > > > >>>>>>>>>> result > > > > of > > > > > >>> an aggregation > > > > > >>> > > > > > > >>> if > > > > > >>> > > > > > > >>>>>>>>>> we want to go down this path. All of this > > > > > >>> > > > > > > >>>>>>>>>> does > > > > > >>> not block this > > > > > >>> > > > > > > >>> KIP > > > > > >>> > > > > > > >>>>>>>>>> and I just wanted to put this aspects up > > > > > >>> > > > > > > >>>>>>>>>> for > > > > > >>> discussion. The > > > > > >>> > > > > > > >>> KIP > > > > > >>> > > > > > > >>>>>>>>>> can limit itself to emit from materialized > > > > > >>> KTables. However, > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> limits should be explicitly stated in the > > > > > >>> > > > > > > >>>>>>>>>> KIP. > > > > > >>> Best, Bruno > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Fri, Jan 24, 2020 at 10:58 AM Matthias > > > > > >>> > > > > > > >>>>>>>>>> J. > > > > Sax > > > > > >>> > > > > > > >>>>>>>>>> <matth...@confluent.io <mailto: > > > > > >>> matth...@confluent.io>> wrote: > > > > > >>> > > > > > > >>>>>>>>>> IMHO, the question about semantics depends > > > > > >>> > > > > > > >>>>>>>>>> on > > > > the > > > > > >>> use case, in > > > > > >>> > > > > > > >>>>>>>>>> particular on the origin of a KTable. If > > > > there is > > > > > >>> a changlog > > > > > >>> > > > > > > >>>>>>>>>> topic that one reads directly into a > > > > > >>> > > > > > > >>>>>>>>>> KTable, > > > > > >>> emit-on-change > > > > > >>> > > > > > > >>> does > > > > > >>> > > > > > > >>>>>>>>>> actually make sense, because the timestamp > > > > > >>> indicates _when_ > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> update was _effective_. For this case, it > > > > > >>> > > > > > > >>>>>>>>>> is > > > > > >>> semantically > > > > > >>> > > > > > sound > > > > > >>> > > > > > > >>>>>>>>>> to _not_ update the timestamp in the store, > > > > > >>> because the second > > > > > >>> > > > > > > >>>>>>>>>> update is actually idempotent and advancing > > > > the > > > > > >>> timestamp is > > > > > >>> > > > > > > >>> not > > > > > >>> > > > > > > >>>>>>>>>> ideal (one could even consider it to be > > > > > >>> > > > > > > >>>>>>>>>> wrong > > > > to > > > > > >>> advance the > > > > > >>> > > > > > > >>>>>>>>>> timestamp) because the "valid time" of the > > > > record > > > > > >>> pair did not > > > > > >>> > > > > > > >>>>>>>>>> change. This reasoning also applies to > > > > > >>> KTable-KTable joins. > > > > > >>> > > > > > > >>>>>>>>>> However, if the KTable is the result of an > > > > > >>> aggregation, I > > > > > >>> > > > > > think > > > > > >>> > > > > > > >>>>>>>>>> emit-on-update is more natural, because the > > > > > >>> timestamp reflects > > > > > >>> > > > > > > >>>>>>>>>> the _last_ time (ie, highest timestamp) of > > > > > >>> > > > > > > >>>>>>>>>> all > > > > > >>> input records > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> contributed to the result. Hence, updating > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> timestamp and > > > > > >>> > > > > > > >>>>>>>>>> emitting a new record actually sounds > > > > > >>> > > > > > > >>>>>>>>>> correct > > > > to > > > > > >>> me. This > > > > > >>> > > > > > > >>> applies > > > > > >>> > > > > > > >>>>>>>>>> to windowed and non-windowed aggregations > > > > IMHO. > > > > > >>> However, > > > > > >>> > > > > > > >>>>>>>>>> considering the argument that the timestamp > > > > > >>> should not be > > > > > >>> > > > > > > >>> update > > > > > >>> > > > > > > >>>>>>>>>> in the first case in the store to begin > > > > > >>> > > > > > > >>>>>>>>>> with, > > > > > >>> both cases are > > > > > >>> > > > > > > >>>>>>>>>> actually the same, and both can be modeled > > > > > >>> > > > > > > >>>>>>>>>> as > > > > > >>> emit-on-change: > > > > > >>> > > > > > > >>> if > > > > > >>> > > > > > > >>>>>>>>>> a `table()` operator does not update the > > > > > >>> timestamp if the > > > > > >>> > > > > > value > > > > > >>> > > > > > > >>>>>>>>>> does not change, there is _no_ change and > > > > > >>> > > > > > > >>>>>>>>>> thus > > > > > >>> nothing is > > > > > >>> > > > > > > >>>>>>>>>> emitted. At the same time, if an > > > > > >>> > > > > > > >>>>>>>>>> aggregation > > > > > >>> operator does > > > > > >>> > > > > > > >>> update > > > > > >>> > > > > > > >>>>>>>>>> the timestamp (even if the value does not > > > > change) > > > > > >>> there _is_ a > > > > > >>> > > > > > > >>>>>>>>>> change and we emit. Note that handling > > > > > >>> out-of-order data for > > > > > >>> > > > > > > >>>>>>>>>> aggregations would also work seamlessly > > > > > >>> > > > > > > >>>>>>>>>> with > > > > this > > > > > >>> approach -- > > > > > >>> > > > > > > >>> for > > > > > >>> > > > > > > >>>>>>>>>> out-of-order records, the timestamp does > > > > > >>> > > > > > > >>>>>>>>>> never > > > > > >>> change, and > > > > > >>> > > > > > > >>> thus, > > > > > >>> > > > > > > >>>>>>>>>> we only emit if the result itself changes. > > > > > >>> Therefore, I would > > > > > >>> > > > > > > >>>>>>>>>> argue that we might not even need any > > > > > >>> > > > > > > >>>>>>>>>> config, > > > > > >>> because the > > > > > >>> > > > > > > >>>>>>>>>> emit-on-change behavior is just correct and > > > > > >>> reduced the > > > > > >>> > > > > > > >>>>>>>>>> downstream load, while our current > > > > > >>> > > > > > > >>>>>>>>>> behavior is > > > > > >>> not ideal (even > > > > > >>> > > > > > > >>> if > > > > > >>> > > > > > > >>>>>>>>>> it's also correct). Thoughts? -Matthias On > > > > > >>> 1/24/20 9:37 AM, > > > > > >>> > > > > > > >>> John > > > > > >>> > > > > > > >>>>>>>>>> Roesler wrote: Hi Bruno, Thanks for that > > > > idea. I > > > > > >>> hadn't > > > > > >>> > > > > > > >>>>>>>>>> considered that option before, and it does > > > > seem > > > > > >>> like that > > > > > >>> > > > > > would > > > > > >>> > > > > > > >>>>>>>>>> be the right place to put it if we think it > > > > might > > > > > >>> be > > > > > >>> > > > > > > >>> semantically > > > > > >>> > > > > > > >>>>>>>>>> important to control on a table-by-table > > > > basis. I > > > > > >>> had been > > > > > >>> > > > > > > >>>>>>>>>> thinking of it less semantically and more > > > > > >>> practically. In the > > > > > >>> > > > > > > >>>>>>>>>> context of a large topology, or more > > > > generally, a > > > > > >>> large > > > > > >>> > > > > > > >>> software > > > > > >>> > > > > > > >>>>>>>>>> system that contains many topologies and > > > > > >>> > > > > > > >>>>>>>>>> other > > > > > >>> event-driven > > > > > >>> > > > > > > >>>>>>>>>> systems, each no-op result becomes an input > > > > that > > > > > >>> is destined > > > > > >>> > > > > > to > > > > > >>> > > > > > > >>>>>>>>>> itself become a no-op result, and so on, > > > > > >>> > > > > > > >>>>>>>>>> all > > > > the > > > > > >>> way through > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> system. Thus, a single pointless processing > > > > > >>> result becomes > > > > > >>> > > > > > > >>>>>>>>>> amplified into a large number of pointless > > > > > >>> computations, cache > > > > > >>> > > > > > > >>>>>>>>>> perturbations, and network and disk I/O > > > > > >>> operations. If you > > > > > >>> > > > > > also > > > > > >>> > > > > > > >>>>>>>>>> consider operations with fan-out > > > > > >>> > > > > > > >>>>>>>>>> implications, > > > > > >>> like branching > > > > > >>> > > > > > > >>> or > > > > > >>> > > > > > > >>>>>>>>>> foreign-key joins, the wasted resources are > > > > > >>> amplified not just > > > > > >>> > > > > > > >>> in > > > > > >>> > > > > > > >>>>>>>>>> proportion to the size of the system, but > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> size of the > > > > > >>> > > > > > > >>> system > > > > > >>> > > > > > > >>>>>>>>>> times the average fan-out (to the power of > > > > > >>> > > > > > > >>>>>>>>>> the > > > > > >>> number of > > > > > >>> > > > > > > >>> fan-out > > > > > >>> > > > > > > >>>>>>>>>> operations on the path(s) through the > > > > system). In > > > > > >>> my time > > > > > >>> > > > > > > >>>>>>>>>> operating such systems, I've observed these > > > > > >>> effects to be very > > > > > >>> > > > > > > >>>>>>>>>> real, and actually, the system and use case > > > > > >>> doesn't have to be > > > > > >>> > > > > > > >>>>>>>>>> very large before the amplification poses > > > > > >>> > > > > > > >>>>>>>>>> an > > > > > >>> existential > > > > > >>> > > > > > threat > > > > > >>> > > > > > > >>>>>>>>>> to the system as a whole. This is the basis > > > > of my > > > > > >>> advocating > > > > > >>> > > > > > > >>> for > > > > > >>> > > > > > > >>>>>>>>>> a simple behavior change, rather than an > > > > opt-in > > > > > >>> config of any > > > > > >>> > > > > > > >>>>>>>>>> kind. It seems like Streams should "do the > > > > right > > > > > >>> thing" for > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> majority use case. My theory (which may be > > > > wrong) > > > > > >>> is that the > > > > > >>> > > > > > > >>>>>>>>>> majority use case is more like "relational > > > > > >>> queries" than "CEP > > > > > >>> > > > > > > >>>>>>>>>> queries". Even if you were doing some > > > > > >>> event-sensitive > > > > > >>> > > > > > > >>>>>>>>>> computation, wouldn't you do them as Stream > > > > > >>> operations (where > > > > > >>> > > > > > > >>>>>>>>>> this feature is inapplicable anyway)? In > > > > keeping > > > > > >>> with the > > > > > >>> > > > > > > >>>>>>>>>> "practical" perspective, I suggested the > > > > opt-out > > > > > >>> config only > > > > > >>> > > > > > in > > > > > >>> > > > > > > >>>>>>>>>> the (I think unlikely) event that filtering > > > > out > > > > > >>> pointless > > > > > >>> > > > > > > >>> updates > > > > > >>> > > > > > > >>>>>>>>>> actually harms performance. I'd also be > > > > perfectly > > > > > >>> fine without > > > > > >>> > > > > > > >>>>>>>>>> the opt-out config. I really think that > > > > (because > > > > > >>> of the > > > > > >>> > > > > > > >>> timestamp > > > > > >>> > > > > > > >>>>>>>>>> semantics work already underway), we're > > > > already > > > > > >>> pre-fetching > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> prior result most of the time, so there > > > > > >>> > > > > > > >>>>>>>>>> would > > > > > >>> actually be very > > > > > >>> > > > > > > >>>>>>>>>> little extra I/O involved in implementing > > > > > >>> emit-on-change. > > > > > >>> > > > > > > >>>>>>>>>> However, we should consider whether my > > > > experience > > > > > >>> is likely to > > > > > >>> > > > > > > >>>>>>>>>> be general. Do you have some use case in > > > > > >>> > > > > > > >>>>>>>>>> mind > > > > for > > > > > >>> which you'd > > > > > >>> > > > > > > >>>>>>>>>> actually want some KTable results to be > > > > > >>> emit-on-update for > > > > > >>> > > > > > > >>>>>>>>>> semantic reasons? Thanks, -John > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Fri, Jan 24, 2020, at 11:02, Bruno > > > > > >>> > > > > > > >>>>>>>>>> Cadonna > > > > > >>> wrote: Hi > > > > > >>> > > > > > > >>> Richard, > > > > > >>> > > > > > > >>>>>>>>>> Thank you for the KIP. I agree with John > > > > > >>> > > > > > > >>>>>>>>>> that > > > > we > > > > > >>> should focus > > > > > >>> > > > > > > >>> on > > > > > >>> > > > > > > >>>>>>>>>> the interface and behavior change in a > > > > > >>> > > > > > > >>>>>>>>>> KIP. We > > > > > >>> can discuss the > > > > > >>> > > > > > > >>>>>>>>>> implementation later. I am also +1 for the > > > > > >>> survey. I had a > > > > > >>> > > > > > > >>>>>>>>>> thought about this. Couldn't we consider > > > > > >>> emit-on-change to be > > > > > >>> > > > > > > >>> one > > > > > >>> > > > > > > >>>>>>>>>> config of suppress (like > > > > > >>> > > > > > > >>>>>>>>>> `untilWindowCloses`)? > > > > > >>> What you > > > > > >>> > > > > > > >>>>>>>>>> basically propose is to suppress updates if > > > > they > > > > > >>> do not change > > > > > >>> > > > > > > >>>>>>>>>> the result. Considering emit on change as a > > > > > >>> flavour of > > > > > >>> > > > > > suppress > > > > > >>> > > > > > > >>>>>>>>>> would be more flexible because it would > > > > specify > > > > > >>> the behavior > > > > > >>> > > > > > > >>>>>>>>>> locally for a KTable instead of globally > > > > > >>> > > > > > > >>>>>>>>>> for > > > > all > > > > > >>> KTables. > > > > > >>> > > > > > > >>>>>>>>>> Additionally, specifying the behavior in > > > > > >>> > > > > > > >>>>>>>>>> one > > > > > >>> place instead of > > > > > >>> > > > > > > >>>>>>>>>> multiple places feels more intuitive and > > > > > >>> consistent to me. > > > > > >>> > > > > > > >>> Best, > > > > > >>> > > > > > > >>>>>>>>>> Bruno On Fri, Jan 24, 2020 at 7:49 AM John > > > > Roesler > > > > > >>> > > > > > > >>>>>>>>>> <vvcep...@apache.org <mailto: > > > > vvcep...@apache.org>> > > > > > >>> wrote: Hi > > > > > >>> > > > > > > >>>>>>>>>> Richard, Thanks for picking this up! I know > > > > of at > > > > > >>> least one > > > > > >>> > > > > > > >>> large > > > > > >>> > > > > > > >>>>>>>>>> community member for which this feature is > > > > > >>> absolutely > > > > > >>> > > > > > > >>> essential. > > > > > >>> > > > > > > >>>>>>>>>> If I understand your two options, it seems > > > > like > > > > > >>> the proposal > > > > > >>> > > > > > is > > > > > >>> > > > > > > >>>>>>>>>> to implement it as a behavior change > > > > regardless, > > > > > >>> and the > > > > > >>> > > > > > > >>> question > > > > > >>> > > > > > > >>>>>>>>>> is whether to provide an opt-out config or > > > > not. > > > > > >>> Given that any > > > > > >>> > > > > > > >>>>>>>>>> implementation of this feature would have > > > > > >>> > > > > > > >>>>>>>>>> some > > > > > >>> performance > > > > > >>> > > > > > > >>> impact > > > > > >>> > > > > > > >>>>>>>>>> under some workloads, and also that we > > > > > >>> > > > > > > >>>>>>>>>> don't > > > > know > > > > > >>> if anyone > > > > > >>> > > > > > > >>>>>>>>>> really depends on emit-on-update time > > > > semantics, > > > > > >>> it seems like > > > > > >>> > > > > > > >>> we > > > > > >>> > > > > > > >>>>>>>>>> should propose to add an opt-out config. > > > > > >>> > > > > > > >>>>>>>>>> Can > > > > you > > > > > >>> update the > > > > > >>> > > > > > KIP > > > > > >>> > > > > > > >>>>>>>>>> to mention the exact config key and > > > > > >>> > > > > > > >>>>>>>>>> value(s) > > > > > >>> you'd propose? > > > > > >>> > > > > > > >>> Just > > > > > >>> > > > > > > >>>>>>>>>> to move the discussion forward, maybe > > > > something > > > > > >>> like: emit.on > > > > > >>> > > > > > > >>> := > > > > > >>> > > > > > > >>>>>>>>>> change|update with the new default being > > > > "change" > > > > > >>> Thanks for > > > > > >>> > > > > > > >>>>>>>>>> pointing out the timestamp issue in > > > > particular. I > > > > > >>> agree that > > > > > >>> > > > > > if > > > > > >>> > > > > > > >>>>>>>>>> we discard the latter update as a no-op, > > > > > >>> > > > > > > >>>>>>>>>> then > > > > we > > > > > >>> also have to > > > > > >>> > > > > > > >>>>>>>>>> discard its timestamp (obviously, we don't > > > > > >>> forward the > > > > > >>> > > > > > > >>> timestamp > > > > > >>> > > > > > > >>>>>>>>>> update, as that's the whole point, but we > > > > > >>> > > > > > > >>>>>>>>>> also > > > > > >>> can't update > > > > > >>> > > > > > the > > > > > >>> > > > > > > >>>>>>>>>> timestamp in the store, as the store must > > > > remain > > > > > >>> consistent > > > > > >>> > > > > > > >>> with > > > > > >>> > > > > > > >>>>>>>>>> what has been emitted). I have to confess > > > > that I > > > > > >>> disagree with > > > > > >>> > > > > > > >>>>>>>>>> your implementation proposal, but it's also > > > > not > > > > > >>> necessary to > > > > > >>> > > > > > > >>>>>>>>>> discuss implementation in the KIP. Maybe it > > > > would > > > > > >>> be less > > > > > >>> > > > > > > >>>>>>>>>> controversial if you just drop that section > > > > for > > > > > >>> now, so that > > > > > >>> > > > > > > >>> the > > > > > >>> > > > > > > >>>>>>>>>> KIP discussion can focus on the behavior > > > > change > > > > > >>> and config. > > > > > >>> > > > > > > >>> Just > > > > > >>> > > > > > > >>>>>>>>>> for reference, there is some research into > > > > this > > > > > >>> domain. For > > > > > >>> > > > > > > >>>>>>>>>> example, see the "Report" section (3.2.3) > > > > > >>> > > > > > > >>>>>>>>>> of > > > > the > > > > > >>> SECRET paper: > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > > > > > >>> > > > > https://nam04.safelinks.protection.outlook.com/?url=http%3A%2F%2Fpeop > > > > > >>> > > > > > > > le.csail.mit.edu > > > > > >>> > > > > > > >>>>>> > > > > > >>> %2Ftatbul%2Fpublications%2Fmaxstream_vldb10.pdf&data > > > > > >>> > > > > > > > =02%7C01%7CThomas.Becker%40tivo.com > > > > > >>> > > > > > > >>>>>> %7Ce0235483b1eb4f259c5c08d7a8d1c16b%7 > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > > > > > >>> > > > > Cd05b7c6912014c0db45d7f1dcc227e4d%7C1%7C1%7C637163491160859282&sdata > > > > > >>> > > > > > > > > > > > > >>> =4dSGIS8jNPAPP7B48r9e%2BUgFh3WdmzVyXhyT63eP8dI%3D&reserved=0 > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > > It might help to round out the proposal if you take > > > > > >>> > > > > > > > a > > > > brief > > > > > >>> > > > > > > >>> survey of > > > > > >>> > > > > > > >>>>>>>>>> the behaviors of other systems, along with > > > > pros > > > > > >>> and cons if > > > > > >>> > > > > > any > > > > > >>> > > > > > > >>>>>>>>>> are reported. Thanks, -John > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> On Fri, Jan 10, 2020, at 22:27, Richard Yu > > > > wrote: > > > > > >>> Hi > > > > > >>> > > > > > everybody! > > > > > >>> > > > > > > >>>>>>>>>> I'd like to propose a change that we > > > > > >>> > > > > > > >>>>>>>>>> probably > > > > > >>> should've added > > > > > >>> > > > > > > >>> for > > > > > >>> > > > > > > >>>>>>>>>> a long time now. The key benefit of this > > > > > >>> > > > > > > >>>>>>>>>> KIP > > > > > >>> would be reduced > > > > > >>> > > > > > > >>>>>>>>>> traffic in Kafka Streams since a lot of > > > > > >>> > > > > > > >>>>>>>>>> no-op > > > > > >>> results would no > > > > > >>> > > > > > > >>>>>>>>>> longer be sent downstream. Here is the KIP > > > > > >>> > > > > > > >>>>>>>>>> for > > > > > >>> reference. > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > > > > > >>> > > > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcwi > > > > > >>> > > > > > > > ki.apache.org > > > > > >>> > > > > > > >>>>>> > > > > > >>> %2Fconfluence%2Fdisplay%2FKAFKA%2FKIP-557%253A%2BAdd%2Bemit > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > > > > > >>> > > > > %2Bon%2Bchange%2Bsupport%2Bfor%2BKafka%2BStreams&data=02%7C01%7CThom > > > > > >>> > > > > > > > as.Becker%40tivo.com > > > > > >>> > > > > > > >>>>>> > > > > %7Ce0235483b1eb4f259c5c08d7a8d1c16b%7Cd05b7c6912014c > > > > > >>> > > > > > > > > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > > > > > >>> > > > > 0db45d7f1dcc227e4d%7C1%7C1%7C637163491160869277&sdata=zYpCSFOsyN4%2B > > > > > >>> > > > > > > > 4rKRZBQ%2FZvcGQ4EINR9Qm6PLsB7EKrc%3D&reserved=0 > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > > Currently, I seek to formalize our approach for this > > > > KIP > > > > > >>> first > > > > > >>> > > > > > > >>> before > > > > > >>> > > > > > > >>>>>>>>>> we determine concrete API additions / > > > > > >>> configurations. Some > > > > > >>> > > > > > > >>>>>>>>>> configs might warrant adding, whiles others > > > > are > > > > > >>> not necessary > > > > > >>> > > > > > > >>>>>>>>>> since adding them would only increase > > > > complexity > > > > > >>> of Kafka > > > > > >>> > > > > > > >>>>>>>>>> Streams. Cheers, Richard > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> ________________________________ This email > > > > and > > > > > >>> any > > > > > >>> > > > > > attachments > > > > > >>> > > > > > > >>>>>>>>>> may contain confidential and privileged > > > > material > > > > > >>> for the sole > > > > > >>> > > > > > > >>> use > > > > > >>> > > > > > > >>>>>>>>>> of the intended recipient. Any review, > > > > copying, or > > > > > >>> > > > > > distribution > > > > > >>> > > > > > > >>>>>>>>>> of this email (or any attachments) by > > > > > >>> > > > > > > >>>>>>>>>> others > > > > is > > > > > >>> prohibited. If > > > > > >>> > > > > > > >>>>>>>>>> you are not the intended recipient, please > > > > > >>> contact the sender > > > > > >>> > > > > > > >>>>>>>>>> immediately and permanently delete this > > > > > >>> > > > > > > >>>>>>>>>> email > > > > and > > > > > >>> any > > > > > >>> > > > > > > >>>>>>>>>> attachments. No employee or agent of TiVo > > > > > >>> > > > > > > >>>>>>>>>> is > > > > > >>> authorized to > > > > > >>> > > > > > > >>>>>>>>>> conclude any binding agreement on behalf of > > > > TiVo > > > > > >>> by email. > > > > > >>> > > > > > > >>>>>>>>>> Binding agreements with TiVo may only be > > > > > >>> > > > > > > >>>>>>>>>> made > > > > by > > > > > >>> a signed > > > > > >>> > > > > > > >>> written > > > > > >>> > > > > > > >>>>>>>>>> agreement. -- *Tommy Becker* *Principal > > > > Engineer * > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> *Personalized Content Discovery* > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> *O* +1 919.460.4747 *tivo.com* < > > > > > >>> http://www.tivo.com/> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>>> This email and any attachments may contain > > > > > >>> confidential and > > > > > >>> > > > > > > >>>>>>>>>> privileged material for the sole use of the > > > > > >>> intended > > > > > >>> > > > > > recipient. > > > > > >>> > > > > > > >>>>>>>>>> Any review, copying, or distribution of > > > > > >>> > > > > > > >>>>>>>>>> this > > > > > >>> email (or any > > > > > >>> > > > > > > >>>>>>>>>> attachments) by others is prohibited. If > > > > > >>> > > > > > > >>>>>>>>>> you > > > > are > > > > > >>> not the > > > > > >>> > > > > > > >>> intended > > > > > >>> > > > > > > >>>>>>>>>> recipient, please contact the sender > > > > immediately > > > > > >>> and > > > > > >>> > > > > > > >>> permanently > > > > > >>> > > > > > > >>>>>>>>>> delete this email and any attachments. No > > > > > >>> employee or agent of > > > > > >>> > > > > > > >>>>>>>>>> TiVo is authorized to conclude any binding > > > > > >>> agreement on behalf > > > > > >>> > > > > > > >>> of > > > > > >>> > > > > > > >>>>>>>>>> TiVo by email. Binding agreements with TiVo > > > > may > > > > > >>> only be made > > > > > >>> > > > > > > >>> by a > > > > > >>> > > > > > > >>>>>>>>>> signed written agreement. > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> -- > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> *Tommy Becker* /Principal Engineer / > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> /Personalized Content Discovery/ > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> *O* +1 919.460.4747 *tivo.com* < > > > > > >>> http://www.tivo.com/> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>>>>> > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > > > > > >>> > > > > ---------------------------------------------------------------------- > > > > > >>> > > > > > > >>>>>>> > > > > > >>> > > > > > > >>>>>> > > > > > >>> > > > > > > >>>>> > > > > > >>> > > > > > > >>>> > > > > > >>> > > > > > > >>> > > > > > >>> > > > > > > >> > > > > > >>> > > > > > > > > > > > > >>> > > > > > > > > > > > >>> > > > > > > > > > > > >>> > > > > > > Attachments: > > > > > >>> > > > > > > * signature.asc > > > > > >>> > > > > > > > > > > >>> > > > > > > > > >>> > > > > > > >>> > > > > > >> > > > > > > > > > > > > >
