Hi John, > Although it's not great to have "special snowflakes" in the API, Choice B does seem safer in the short term. We would basically be proposing a temporary API to make the suppressed view queriable without a Materialized argument.
Then, it seems like you prefer `KTable#suppress(Suppressed, String)` (i.e., queriable name only as a parameter) for this time, and refine API with the other related KIPs later. Do I understand correctly? Thanks, Dongjin On Wed, Sep 16, 2020 at 2:17 AM John Roesler <vvcep...@apache.org> wrote: > Hi Dongjin, > > Thanks for presenting these options. The concern that > Matthias brought up is a very deep problem that afflicts all > operations downstream of windowing operations. It's the same > thing that derailed KIP-300. For the larger context, I have > developed a couple of approaches to resolve this situation, > but I think it makes sense to finish up KIP-478 before > presenting them. > > However, I don't think that we need in particular to block > the current proposal on solving that long-running and deep > issue with the DSL. Instead, we should make a top-level > decision whether to: > > A: Make Suppress just like all the other KTable operations. > It will have the same pathological behavior that the keyset > is unbounded while the store implementation is only a > KeyValueStore. Again, this exact pathology currently affects > all KTable operations that follow from windowing operations. > For example, it applies to the current workaround that > Dongjin documented in the KIP: > suppress().filter(Materialized<KeyValueStore>). This is > Option 2 that Dongjin presented. > > B: Do something different with Suppress in order to side- > step the problem. For example, Suppress does not _need_ to > have a separate state store at all. If we just give people a > switch to make the operation queriable, we can implement a > ReadOnlyKeyValueStore interface by querying the "priorValue" > of the buffer first and then querying the upstream > ValueGetter. This broad category of "do something different > with Suppress" encompases Option 1 and Option 3 that Dongjin > presented. > > > Speaking personally, I think Choice A would be the most > obvious and least weird choice, but it presents a serious > risk of escalating the severity of the problem of unbounded > state. This is currently a risk that we're aware of, but has > not yet become a big problem in practice. As Matthias > pointed out, Suppress is far more likely to be used > downstream of windowed tables than other operations, so > having a Materialized<KVStore> overload has the significant > risk of getting people into a bad state. Note, broadly > advertising the workaround from the KIP would have the exact > same impact, so we should be careful about recommending it. > > Although it's not great to have "special snowflakes" in the > API, Choice B does seem safer in the short term. We would > basically be proposing a temporary API to make the > suppressed view queriable without a Materialized argument. > Then, once we fix the main KIP-300 problem, we would look at > converging Suppress with the rest of the KTable > materialization APIs. > > WDYT? > Thanks, > -John > > > On Wed, 2020-09-16 at 00:01 +0900, Dongjin Lee wrote: > > Hi Matthias, > > > > Thank you very much for the detailed feedback. Here are my opinions: > > > > > Because there is no final result for non-windowed KTables, it seems > that > > this new feature only make sense for the windowed-aggregation case? > > > > I think a little bit different. Of course, for windowed KTable, this > > feature provides the final state; for non-windowed KTables, it provides a > > view to the records received more than the predefined waiting time ago - > > excluding the records that are waiting for more events. > > > > > Thus, the signature of `Materialized` should take a `WindowStore` > instead > > of a `KeyValueStore`? > > > > I reviewed the implementation following your comments and found the > > following: > > > > 1. `Materialized` instance includes the following: KeySerde, ValueSerde, > > StoreSupplier, and Queriable Name. > > 2. The other `Materialized` method variants in `KTable` are making use of > > KeySerde, ValueSerde, and Queriable Name only. (That is, StoreSupplier is > > ignored.) > > 3. `KTable#suppress(Suppressed, Materialized)` uses the Queriable Name > > only. StoreSupplier is also ignored. > > > > So, we have three choices for the method signature: > > > > 1. `KTable#suppress(Suppressed, String)` (i.e., passing the Queriable > Name > > only): > > > > This is the simplest; however, it is inconsistent with the other > > Materialized variant methods. > > > > 2. `KTable#suppress(Suppressed, Materialized<K, V, KeyValueStore>)` > (i.e., > > current proposal) > > > > This approach is harmless at this point, for StoreSupplier is ignored; > > However, since suppression can be used to both of `KeyValueStore` and > > `WindowStore`, this approach is not only weird but also leaving some > > potential risk to the future. (On second thoughts, I agree, this API > design > > is bad and dangerous.) > > > > 3. `KTable#suppress(Suppressed, Materialized<K, V, StateStore>)` > > > > This approach embraces both of `KeyValueStore` and `WindowStore` cases. > > Since the concrete class type of `Suppressed` instance differs for the > > `StateStore`[^1], it seems like we can validate the arguments on the > method > > call. (e.g., throw `IllegalArgumentException` if when `Suppressed` > instance > > on `KeyValueStore` is given with `Materialized` instance of > `WindowStore`.) > > This approach not only breaks the API consistency but also guards from a > > miss-usage of the API. > > > > How do you think? I am now making a try on the third approach. > > > > Thanks, > > Dongjin > > > > [^1]: `SuppressedInternal` for `KeyValueStore` and > > `FinalResultsSuppressionBuilder` for `WindowStore`. > > > > On Sat, Sep 12, 2020 at 3:29 AM Matthias J. Sax <mj...@apache.org> > wrote: > > > > > Thanks for updating the KIP. > > > > > > I think there is still one open question. `suppress()` can be used on > > > non-windowed KTable for rate control, as well as on a windowed-KTable > > > (also for rate control, but actually mainly) for only emitting the > final > > > result of a windowed aggregation. For the non-windowed case, we use a > > > KeyValueStore while for the windowed cases, we use a WindowStore. > > > > > > Because there is no final result for non-windowed KTables, it seems > that > > > this new feature only make sense for the windowed-aggregation case? > > > Thus, the signature of `Materialized` should take a `WindowStore` > > > instead of a `KeyValueStore`? > > > > > > If that's correct, I am wondering: > > > > > > - Can we guard from a miss-usage of the API if the upstream KTable is > > > not windowed (or maybe it's not necessary to guard)? > > > - Can we actually implement it? We had issues with regard to KIP-300 > to > > > materialize windowed-KTables? > > > > > > Would be worth to clarify upfront. Maybe, we even need a POC > > > implementation to verify that it works? > > > > > > > > > -Matthias > > > > > > > > > On 9/11/20 12:26 AM, Dongjin Lee wrote: > > > > Hi All, > > > > > > > > Here is the voting thread: > > > > > > > > > > > https://lists.apache.org/thread.html/r5653bf2dafbb27b247bf20dbe6f070c151b3823d96c9c9ca94183e20%40%3Cdev.kafka.apache.org%3E > > > > Thanks, > > > > Dongjin > > > > > > > > On Fri, Sep 11, 2020 at 4:23 PM Dongjin Lee <dong...@apache.org> > wrote: > > > > > > > > > Hi John, > > > > > > > > > > Thanks for the feedback. I will open the Vote thread now. > > > > > > > > > > Best, > > > > > Dongjin > > > > > > > > > > On Fri, Sep 11, 2020 at 2:00 AM John Roesler <vvcep...@apache.org> > > > wrote: > > > > > > Hi Dongjin, > > > > > > > > > > > > Sorry for the delay. I'm glad you're still pushing this > > > > > > forward. It would be nice to get this in to the 2.7 release. > > > > > > > > > > > > I just took another look at the KIP, and it looks good to > > > > > > me! > > > > > > > > > > > > I think this is ready for a vote. > > > > > > > > > > > > Thanks, > > > > > > -John > > > > > > > > > > > > On Wed, 2020-08-05 at 22:04 +0900, Dongjin Lee wrote: > > > > > > > Hi All, > > > > > > > > > > > > > > I updated the KIP > > > > > > > < > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-508%3A+Make+Suppression+State+Queriable > > > > > > > and the implementation, following the discussion here. > > > > > > > > > > > > > > You must be working hard preparing the release of 2.6.0, so > please > > > have > > > > > > a > > > > > > > look after your work is done. > > > > > > > > > > > > > > Thanks, > > > > > > > Dongjin > > > > > > > > > > > > > > On Sun, Mar 8, 2020 at 12:20 PM John Roesler < > vvcep...@apache.org> > > > > > > wrote: > > > > > > > > Thanks Matthias, > > > > > > > > > > > > > > > > Good idea. I've changed the ticket name and added a note > > > > > > > > clarifying that this ticket is not the same as > > > > > > > > https://issues.apache.org/jira/browse/KAFKA-7224 > > > > > > > > > > > > > > > > Incidentally, I learned that I never documented my reasons > > > > > > > > for abandoning my work on KAFKA-7224 ! I've now updated > > > > > > > > that ticket, too, so your question had an unexpected > side-benefit. > > > > > > > > > > > > > > > > Thanks, > > > > > > > > -John > > > > > > > > > > > > > > > > On Sat, Mar 7, 2020, at 18:01, Matthias J. Sax wrote: > > > > Thanks for clarification. > > > > > > > > Can you maybe update the Jira ticket? Do we have a ticket for > > > > spill-to-disk? Maybe link to it and explain that it's two different > > > > things? Maybe even rename the ticket to something more clear, ie, > > > > "make suppress result queryable" or simliar? > > > > > > > > > > > > -Matthias > > > > > > > > On 3/7/20 1:58 PM, John Roesler wrote: > > > > > > > > > > > Hey Matthias, > > > > > > > > > > > > > > > > > > > > > > I’m sorry if the ticket was poorly stated. The ticket > is to add a > > > > DSL overload to pass a Materialized argument to suppress. As a > > > > > > > result, > > > > the result of the suppression would be queriable. > > > > > > > > > > > This is unrelated to “persistent buffer” aka > “spill-to-disk”. > > > > > > > > > > > > > > > > > > > > > > There was some confusion before about whether this > ticket could be > > > > implemented as “query the buffer”. Maybe it can, but not trivially. > > > > The obvious way is just to add a new state store which we write the > > > > results into just before we forward. I.e., it’s exactly like the > > > > materialized variant of any stateless KTable operation. > > > > > > > > > > > Thanks, John > > > > > > > > > > > > > > > > > > > > > > On Sat, Mar 7, 2020, at 15:32, Matthias J. Sax wrote: > Thanks for > > > > > > > > > > > the KIP Dongjin, > > > > > > > > > > > > > > > > > > > > > > I am still not sure if I can follow, what might also > be caused by > > > > > > > > > > > the backing JIRA ticket (maybe John can clarify the > intent of the > > > > > > > > > > > ticket as he created it): > > > > > > > > > > > > > > > > > > > > > > Currently, suppress() only uses an in-memory buffer > and my > > > > > > > > > > > understanding of the Jira is, to add the ability to > use a > > > > > > > > > > > persistent buffer (ie, spill to disk backed by > RocksDB). > > > > > > > > > > > > > > > > > > > > > > Adding a persistent buffer is completely unrelated to > allow > > > > > > > > > > > querying the buffer. In fact, one could query an > in-memory buffer, > > > > > > > > > > > too. However, querying the buffer does not really seem > to be > > > > > > > useful > > > > > > > > > > > as pointed out by John, as you can always query the > upstream > > > > > > > KTable > > > > > > > > > > > store. > > > > > > > > > > > > > > > > > > > > > > Also note that for the emit-on-window-close case the > result is > > > > > > > > > > > deleted from the buffer when it is emitted, and thus > cannot be > > > > > > > > > > > queried any longe r. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Can you please clarify if you intend to allow spilling > to disk or > > > > > > > > > > > if you intent to enable IQ (even if I don't see why > querying make > > > > > > > > > > > sense, as the data is either upstream or deleted). > Also, if you > > > > > > > > > > > want to enable IQ, why do we need all those new > interfaces? The > > > > > > > > > > > result of a suppress() is a KTable that is the same as > any other > > > > > > > > > > > key-value/windowed/sessions store? > > > > > > > > > > > > > > > > > > > > > > We should also have corresponding Jira tickets for > different cases > > > > > > > > > > > to avoid the confusion I am in atm :) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -Matthias > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On 2/27/20 8:21 AM, John Roesler wrote: > > > > > > > > > > > > > > Hi Dongjin, > > > > > > > > > > > > > > > > > > > > > > > > > > > > No problem; glad we got it sorted out. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks again for picking this up! -John > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Feb 26, 2020, at 09:24, Dongjin Lee > wrote: > > > > > > > > > > > > > > > > I was under the impression that you wanted > to expand the > > > > > > > > > > > > > > > > scope of the KIP > > > > > > > > > > > > > > > to additionally allow querying the internal > buffer, not > > > > > > > > > > > > > > > just the result. Can you clarify whether you > are proposing > > > > > > > > > > > > > > > to allow querying the state of the internal > buffer, the > > > > > > > > > > > > > > > result, or both? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Sorry for the confusion. As we already talked > with, we > > > > > > > only > > > > > > > > > > > > > > > need to query the suppressed output, not the > internal > > > > > > > > > > > > > > > buffer. The current implementation is wrong. > After > > > > > > > refining > > > > > > > > > > > > > > > the KIP and implementation accordingly I will > notify you - > > > > > > > > > > > > > > > I must be confused, also. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, Dongjin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Feb 25, 2020 at 12:17 AM John Roesler > > > > > > > > > > > > > > > <vvcep...@apache.org> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Dongjin, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Ah, I think I may have been confused. I 100% > agree that > > > > > > > > > > > > > > > > we need a materialized variant for > suppress(). Then, you > > > > > > > > > > > > > > > > could do: ...suppress(..., > > > > > > > > > > > > > > > > Materialized.as(“final-count”)) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > If that’s your proposal, then we are on the > same page. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I was under the impression that you wanted > to expand the > > > > > > > > > > > > > > > > scope of the KIP to additionally allow > querying the > > > > > > > > > > > > > > > > internal buffer, not just the result. Can > you clarify > > > > > > > > > > > > > > > > whether you are proposing to allow querying > the state of > > > > > > > > > > > > > > > > the internal buffer, the result, or both? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, John > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Feb 20, 2020, at 08:41, Dongjin Lee > wrote: > > > > > > > > > > > > > > > > > Hi John, Thanks for your kind explanation > with an > > > > > > > > > > > > > > > > > example. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > But it feels like you're saying you're > trying to do > > > > > > > > > > > > > > > > > > something different > > > > > > > > > > > > > > > > > than just query the windowed key and get > back the > > > > > > > > > > > > > > > > > current count? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Yes, for example, what if we need to > retrieve the (all > > > > > > > > > > > > > > > > > or range) keys > > > > > > > > > > > > > > > > with > > > > > > > > > > > > > > > > > a closed window? In this example, let's > imagine we > > > > > > > need > > > > > > > > > > > > > > > > > to retrieve only (key=A, window=10), not > (key=A, > > > > > > > > > > > > > > > > > window=20). > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Of course, the value accompanied by a > flushed key is > > > > > > > > > > > > > > > > > exactly the same to the one in the > upstream KTable; > > > > > > > > > > > > > > > > > However, if our intention is not pointing > out a > > > > > > > > > > > > > > > > > specific key but retrieving a group of > unspecified > > > > > > > > > > > > > > > > > keys, we stuck > > > > > > > > > > > > > > > > in > > > > > > > > > > > > > > > > > trouble - since we can't be sure which key > is flushed > > > > > > > > > > > > > > > > > out beforehand. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > One workaround would be materializing it > with > > > > > > > > > > > > > > > > > `suppressed.filter(e -> > > > > > > > > > > > > > > > > true, > > > > > > > > > > > > > > > > > Materialized.as("final-count"))`. But I > think > > > > > > > providing > > > > > > > > > > > > > > > > > a materialized variant for suppress method > is better > > > > > > > > > > > > > > > > > than this workaround. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, Dongjin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Feb 20, 2020 at 1:26 AM John > Roesler > > > > > > > > > > > > > > > > > <vvcep...@apache.org> > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > Thanks for the response, Dongjin, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'm sorry, but I'm still not following. > It seems > > > > > > > like > > > > > > > > > > > > > > > > > > the view you > > > > > > > > > > > > > > > > would > > > > > > > > > > > > > > > > > > get on the "current state of the buffer" > would > > > > > > > always > > > > > > > > > > > > > > > > > > be equivalent to the view of the > upstream table. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Let me try an example, and maybe you can > point out > > > > > > > > > > > > > > > > > > the flaw in my reasoning. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Let's say we're doing 10 ms windows with > a grace > > > > > > > > > > > > > > > > > > period of zero. Let's also say we're > computing a > > > > > > > > > > > > > > > > > > windowed count, and that we have a > "final results" > > > > > > > > > > > > > > > > > > suppression after the count. Let's > materialize the > > > > > > > > > > > > > > > > > > count as "Count" and the suppressed > result as "Final > > > > > > > > > > > > > > > > > > Count". > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Suppose we get an input event: (time=10, > key=A, > > > > > > > > > > > > > > > > > > value=...) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Then, Count will look like: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 1 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The (internal) suppression buffer will > contain: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 1 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The record is still buffered because the > window > > > > > > > > > > > > > > > > > > isn't closed yet. Final Count is an > empty table: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --------------- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Now, we get a second event: (time=15, > key=A, > > > > > > > > > > > > > > > > > > value=...) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Then, Count will look like: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 2 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The (internal) suppression buffer will > contain: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 2 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The record is still buffered because the > window > > > > > > > > > > > > > > > > > > isn't closed yet. Final Count is an > empty table: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --------------- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Finally, we get a third event: (time=20, > key=A, > > > > > > > > > > > > > > > > > > value=...) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Then, Count will look like: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 2 | | > > > > > > > > > > > > > > > > > > 20 | A | 1 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The (internal) suppression buffer will > contain: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 20 | A > | 1 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Note that window 10 has been flushed > out, because > > > > > > > > > > > > > > > > > > it's now closed. And window 20 is > buffered because > > > > > > > it > > > > > > > > > > > > > > > > > > isn't closed yet. Final Count is now: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > window | key | value | | 10 | A > | 2 | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --------------- > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Reading your email, I can't figure out > what value > > > > > > > > > > > > > > > > > > there is in querying > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > internal suppression buffer, since it > only contains > > > > > > > > > > > > > > > > > > exactly the same > > > > > > > > > > > > > > > > value > > > > > > > > > > > > > > > > > > as the upstream table, for each key that > is still > > > > > > > > > > > > > > > > > > buffered. But it feels > > > > > > > > > > > > > > > > like > > > > > > > > > > > > > > > > > > you're saying you're trying to do > something > > > > > > > different > > > > > > > > > > > > > > > > > > than just query > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > windowed key and get back the current > count? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, -John > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Feb 19, 2020, at 09:49, Dongjin > Lee wrote: > > > > > > > > > > > > > > > > > > > Hi John, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 'The intermediate state of the > suppression' in KIP > > > > > > > > > > > > > > > > > > > does not mean the > > > > > > > > > > > > > > > > > > state > > > > > > > > > > > > > > > > > > > of upstream KTable - sure, the state > of the > > > > > > > > > > > > > > > > > > > upstream KTable can be > > > > > > > > > > > > > > > > > > queried > > > > > > > > > > > > > > > > > > > by materializing the operator > immediately before > > > > > > > > > > > > > > > > > > > the suppress as you > > > > > > > > > > > > > > > > > > shown. > > > > > > > > > > > > > > > > > > > What I meant in KIP was the final > state of the > > > > > > > > > > > > > > > > > > > buffer, which is not > > > > > > > > > > > > > > > > > > emitted > > > > > > > > > > > > > > > > > > > yet. (I agree, the current description > may be > > > > > > > > > > > > > > > > > > > confusing; it would be > > > > > > > > > > > > > > > > > > better > > > > > > > > > > > > > > > > > > > to change it with 'the current state > of the > > > > > > > > > > > > > > > > > > > suppression' or 'the > > > > > > > > > > > > > > > > results > > > > > > > > > > > > > > > > > > of > > > > > > > > > > > > > > > > > > > the suppression', like the Jira issue > > > > > > > > > > > > > > > > > > > < > https://issues.apache.org/jira/browse/KAFKA-8403 > > > > > > > > > > > > > > > > > > > states.) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > For a little bit more about the > motivation, here > > > > > > > is > > > > > > > > > > > > > > > > > > > one of my > > > > > > > > > > > > > > > > > > experience: I > > > > > > > > > > > > > > > > > > > had to build a monitoring application > which > > > > > > > > > > > > > > > > > > > collects signals from IoT devices > (say, a > > > > > > > > > > > > > > > > > > > semiconductor production line.) If the > number of > > > > > > > > > > > > > > > > > > collected > > > > > > > > > > > > > > > > > > > signals within the time window is much > less than > > > > > > > > > > > > > > > > > > > the expected, there > > > > > > > > > > > > > > > > may > > > > > > > > > > > > > > > > > > be > > > > > > > > > > > > > > > > > > > some problems like network hiccup in > the systems. > > > > > > > > > > > > > > > > > > > We wanted to build > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > > system in the form of a dashboard, but > could not > > > > > > > by > > > > > > > > > > > > > > > > > > > lack of > > > > > > > > > > > > > > > > materializing > > > > > > > > > > > > > > > > > > > feature. It was precisely the case of > querying > > > > > > > only > > > > > > > > > > > > > > > > > > > the final > > > > > > > > > > > > > > > > results of > > > > > > > > > > > > > > > > > > a > > > > > > > > > > > > > > > > > > > windowed aggregation, as the Jira issue > > > > > > > > > > > > > > > > > > > < > https://issues.apache.org/jira/browse/KAFKA-8403 > > > > > > > > > > > > > > > > > > > states. We > > > > > > > > > > > > > > > > finally > > > > > > > > > > > > > > > > > > ended > > > > > > > > > > > > > > > > > > > in implementing the system in an email > alerting > > > > > > > > > > > > > > > > > > > system like this < > > > > > > > > https://www.confluent.io/blog/kafka-streams-take-on-watermarks-an > > > > d-t > > > > riggers/ > > > > > > > > > > > and had to collect the keys and windows of trouble by > hand. > > > > > > > > > > > > > > > > > > > I think these kinds of use cases would > be much > > > > > > > > > > > > > > > > > > > common. Should it be described in the > KIP much > > > > > > > more > > > > > > > > > > > > > > > > > > > in detail? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, Dongjin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sat, Feb 15, 2020 at 4:43 AM John > Roesler > > > > > > > > > > > > > > > > > > > <vvcep...@apache.org> > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > Hi Dongjin, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the KIP! > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Can you explain more about why the > internal data > > > > > > > > > > > > > > > > > > > > structures of > > > > > > > > > > > > > > > > > > suppression > > > > > > > > > > > > > > > > > > > > should be queriable? The motivation > just says > > > > > > > > > > > > > > > > > > > > that users might > > > > > > > > > > > > > > > > want to > > > > > > > > > > > > > > > > > > do > > > > > > > > > > > > > > > > > > > > it, which seems like it could > justify literally > > > > > > > > > > > > > > > > > > > > anything :) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > One design point of Suppression is > that if you > > > > > > > > > > > > > > > > > > > > wanted to query the > > > > > > > > > > > > > > > > > > “final > > > > > > > > > > > > > > > > > > > > state”, you can Materialize the > suppress itself > > > > > > > > > > > > > > > > > > > > (which is why it > > > > > > > > > > > > > > > > needs > > > > > > > > > > > > > > > > > > the > > > > > > > > > > > > > > > > > > > > variant); if you wanted to query the > > > > > > > > > > > > > > > > > > > > “intermediate state”, you can > materialize the > > > > > > > > > > > > > > > > > > > > operator immediately before the > suppress. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Example: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ...count(Materialized.as(“intermediate”)) > > > > > > > > > > > > > > > > > > > > .supress(untilWindowClosed(), > > > > > > > > > > > > > > > > > > > > Materialized.as(“final”)) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I’m not sure what use case would > require > > > > > > > > > > > > > > > > > > > > actually fetching from the internal > buffers. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, John > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Feb 14, 2020, at 07:55, > Dongjin Lee > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Hi devs, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I'd like to reboot the discussion > on KIP-508, > > > > > > > > > > > > > > > > > > > > > which aims to > > > > > > > > > > > > > > > > support a > > > > > > > > > > > > > > > > > > > > > Materialized variant of > KTable#suppress. It > > > > > > > > > > > > > > > > > > > > > was initially > > > > > > > > > > > > > > > > submitted > > > > > > > > > > > > > > > > > > > > several > > > > > > > > > > > > > > > > > > > > > months ago but closed by the > inactivity. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - KIP: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-508%3A+Make > > > > +Su > > > > ppression+State+Queriable > > > > > > > > > > > - Jira: > https://issues.apache.org/jira/browse/KAFKA-8403 > > > > > > > > > > > > > > > > > > > > > All kinds of feedback will be > greatly > > > > > > > > > > > > > > > > > > > > > appreciated. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Best, Dongjin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- *Dongjin Lee* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > *A hitchhiker in the mathematical > world.* > > > > > > > > > > > > > > > > > > > > > *github: > > > > > > > > > > > > > > > > > > > > > <http://goog_969573159/> > > > > > > > github.com/dongjinleekr > > > > > > > > > > > > > > > > > > > > > > > > > <https://github.com/dongjinleekr>linkedin: > > > > > > > > > > > > > > > > > > > > kr.linkedin.com/in/dongjinleekr > > > > > > > > > > > > > > > > > > > > > < > https://kr.linkedin.com/in/dongjinleekr > > > > > > > > speakerdeck: > > > > speakerdeck.com/dongjin > > > > > > > > > > > > > > > > > > > > > <https://speakerdeck.com/dongjin>* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- *Dongjin Lee* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > *A hitchhiker in the mathematical > world.* *github: > > > > > > > > > > > > > > > > > > > <http://goog_969573159/> > github.com/dongjinleekr > > > > > > > > > > > > > > > > > > > <https://github.com/dongjinleekr > >linkedin: > > > > > > > > > > > > > > > > > > kr.linkedin.com/in/dongjinleekr > > > > > > > > > > > > > > > > > > > < > https://kr.linkedin.com/in/dongjinleekr > > > > > > > > speakerdeck: > > > > speakerdeck.com/dongjin > > > > > > > > > > > > > > > > > > > <https://speakerdeck.com/dongjin>* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- *Dongjin Lee* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > *A hitchhiker in the mathematical world.* > *github: > > > > > > > > > > > > > > > > > <http://goog_969573159/> > github.com/dongjinleekr > > > > > > > > > > > > > > > > > <https://github.com/dongjinleekr>linkedin: > > > > > > > > > > > > > > > > kr.linkedin.com/in/dongjinleekr > > > > > > > > > > > > > > > > > <https://kr.linkedin.com/in/dongjinleekr > >speakerdeck: > > > > > > > > > > > > > > > > speakerdeck.com/dongjin > > > > > > > > > > > > > > > > > <https://speakerdeck.com/dongjin>* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- *Dongjin Lee* > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > *A hitchhiker in the mathematical world.* > *github: > > > > > > > > > > > > > > > <http://goog_969573159/> > github.com/dongjinleekr > > > > > > > > > > > > > > > <https://github.com/dongjinleekr>linkedin: > > > > > > > > > > > > > > > kr.linkedin.com/in/dongjinleekr > > > > > > > > > > > > > > > <https://kr.linkedin.com/in/dongjinleekr > >speakerdeck: > > > > > > > > > > > > > > > speakerdeck.com/dongjin < > https://speakerdeck.com/dongjin > > > > > > > > * > > > > > > > > > > -- > > > > > *Dongjin Lee* > > > > > > > > > > *A hitchhiker in the mathematical world.* > > > > > > > > > > > > > > > > > > > > > > > > > *github: <http://goog_969573159/>github.com/dongjinleekr > > > > > <https://github.com/dongjinleekr>keybase: > > > https://keybase.io/dongjinleekr > > > > > <https://keybase.io/dongjinleekr>linkedin: > > > kr.linkedin.com/in/dongjinleekr > > > > > <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: > > > speakerdeck.com/dongjin > > > > > <https://speakerdeck.com/dongjin>* > > > > > > > -- *Dongjin Lee* *A hitchhiker in the mathematical world.* *github: <http://goog_969573159/>github.com/dongjinleekr <https://github.com/dongjinleekr>keybase: https://keybase.io/dongjinleekr <https://keybase.io/dongjinleekr>linkedin: kr.linkedin.com/in/dongjinleekr <https://kr.linkedin.com/in/dongjinleekr>speakerdeck: speakerdeck.com/dongjin <https://speakerdeck.com/dongjin>*
