Hi Aljoscha, Thanks for the explanation, and sorry for late reply was busy with work.
I did think about this scenario, in fact in my previous mail I thought of posting this question, then I understood that this problem will be there which ever method we choose(Trigger looking for pattern or Window looking for pattern). I do have a pretty good watermark but my concern is that it changes based on the key of these messages(I don't know if it is possible, haven't started coding that yet. May be you could tell me). Even if it is yes some of these watermarks will be long(in days), which I don't want the trigger to wait that long. It looks like it is not easy to have an evictAfter based on window function(without introducing coupling), but can the current window apply function be modified to allow it to change the elements in it - may be using some state backend(I don't know how excatly the internals of these work, so this might be a wrong question) Thanks and Regards, Vishnu Viswanath, On Fri, Jul 8, 2016 at 10:20 AM, Aljoscha Krettek <aljos...@apache.org> wrote: > Hi Vishnu, > how long would these patterns be? The Trigger would not have to sort the > elements for every new element but just insert the new element into an > internal data structure. Only when it sees that the watermark is past a > certain point would it check whether the pattern matches and actually > Trigger. > > A general note regarding order and event time: I think relying on this for > computation is very tricky unless the watermark is 100 % correct or you > completely discard elements that arrive after the watermark, i.e. elements > that would break the promise of the watermark that no elements with an > earlier timestamp will ever arrive. The reason for this is that there could > always enter new elements that end up between already seen elements. For > example, let's say we have this sequence of elements when the trigger > fires: > > a-b-a > > This is the sequence that you are looking for and you emit some result from > the WindowFunction. Now, new elements arrive that fall in between the > elements we already have: > > a-d-e-b-f-g-a > > This is an updated, sorted view of the actual event-time stream and we > didn't realize that the stream actually looks like this before. Does this > still match the original pattern or should we now consider this as > non-matching? If no, then the earlier successful match for a-b-a was wrong > and we should never have processed it but we didn't know at the time. If > yes, then pattern matching like this can be done in the Trigger by having > something like pattern slots: You don't have to store all elements in the > Trigger, you just need to store possible candidates that could match the > pattern and ignore the other (in-between) elements. > > Cheers, > Aljoscha > > On Fri, 8 Jul 2016 at 14:10 Vishnu Viswanath <vishnu.viswanat...@gmail.com > > > wrote: > > > Hi Aljoscha, > > > > That is a good idea, trying to tie it back to the use case, > > e.g., suppose trigger is looking for a pattern, a-b-a and when it sees > such > > a pattern, it will trigger the window and it knows that now the Evictor > is > > going to evict the element b, and trigger updates its state as a-a (even > > before the window & evictor completes) and will be looking for the rest > of > > the pattern i.e., b-a. But I can think of 1 problem here, > > > > - the events can arrive out of order, i.e., the trigger might be > seeing > > a pattern a-a-b but actual event time is a-b-a then trigger will have > to > > sort the elements in the window everytime it sees an element. (I was > > planning to do this sorting in the window, which will be less often - > > only > > when the trigger fires) > > > > Thanks and Regards, > > Vishnu Viswanath, > > > > On Fri, Jul 8, 2016 at 6:04 AM, Aljoscha Krettek <aljos...@apache.org> > > wrote: > > > > Hi, > > > come to think of it, the right place to put such checks is actually the > > > Trigger. It would have to be a custom trigger that observes time but > also > > > keeps some internal state machine to decide when it has observed the > > right > > > pattern in the window. Then the window function would just have to do > the > > > processing and you have good separation of concerns. Does that make > > sense? > > > > > > I'm ignoring time and sorting by time for now because we probably need > > > another design document for that. To me it seems like a bigger thing. > > > > > > Cheers, > > > Aljoscha > > > > > > On Thu, 7 Jul 2016 at 23:56 Vishnu Viswanath < > > vishnu.viswanat...@gmail.com > > > > > > > wrote: > > > > > > > Hi, > > > > > > > > Regarding the evictAfter function, that evicts based on some decision > > > made > > > > by the window function: I think it will be nice if we can come up > with > > > > something that is LESS coupled, because I can think of several use > > cases > > > > that depend on it. > > > > > > > > Especially in the case where there are late arriving messages. Only > > after > > > > the window function is applied we could tell what to do with the > > elements > > > > in the window. You could apply your business logic there to determine > > if > > > > the window funciton was able to do what it is supposed to do, if yes > > > evict > > > > those elements, else(since the elements you are looking for haven't > > > arrived > > > > yet) wait and try again when the trigger gets fired next time. > > > > > > > > Thanks and Regards, > > > > Vishnu Viswanath, > > > > > > > > > > > > On Thu, Jul 7, 2016 at 9:19 AM, Radu Tudoran < > radu.tudo...@huawei.com> > > > > wrote: > > > > > > > > > Hi, > > > > > > > > > > @Aljoscha - I can understand the reason why you are hesitant to > > > introduce > > > > > "slower" windows such as the ones that would maintain sorted items > or > > > > > windows with bindings between the different entities (evictor, > > trigger, > > > > > window, apply function). However, I think it's possible just to > > create > > > > more > > > > > types of windows. The existing ones (timewindows, global windows > ...) > > > can > > > > > remain, and just add some more flavors of windows were more > features > > > are > > > > > enabled or more functionality (e.g., access to the each element in > > the > > > > > evictor ; possibility to delete or mark for eviction elements in > the > > > > > function...) > > > > > > > > > > Regarding the specific case of sorted windows, I think the N lon N > > > > > complexity to sort (the worst case) is very unlikely. In fact you > > have > > > > > almost sorted items/arrays. Moreover, if you consider that in > > > iteration X > > > > > all elements were sorted, then in iteration X+1 you will need to > sort > > > > just > > > > > the newly arrived elements (M). I would expect that this number M > > might > > > > be > > > > > significant smaller then N (elements that exists). Then using an > > > > insertion > > > > > sort for these new elements you would have M * N complexity and if > > > M<< N > > > > > then the complexity is O(N). Alternatively you can use a binary > > search > > > > for > > > > > insertion and then you further reduce the complexity to O(logN). > > > > > If M is proportional to N then you can sort M and use merge sort > for > > > > > combining. > > > > > > > > > > > > > > > Dr. Radu Tudoran > > > > > Research Engineer - Big Data Expert > > > > > IT R&D Division > > > > > > > > > > > > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH > > > > > European Research Center > > > > > Riesstrasse 25, 80992 München > > > > > > > > > > E-mail: radu.tudo...@huawei.com > > > > > Mobile: +49 15209084330 > > > > > Telephone: +49 891588344173 > > > > > > > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH > > > > > Hansaallee 205, 40549 Düsseldorf, Germany, www.huawei.com > > > > > Registered Office: Düsseldorf, Register Court Düsseldorf, HRB > 56063, > > > > > Managing Director: Bo PENG, Wanzhou MENG, Lifang CHEN > > > > > Sitz der Gesellschaft: Düsseldorf, Amtsgericht Düsseldorf, HRB > 56063, > > > > > Geschäftsführer: Bo PENG, Wanzhou MENG, Lifang CHEN > > > > > This e-mail and its attachments contain confidential information > from > > > > > HUAWEI, which is intended only for the person or entity whose > address > > > is > > > > > listed above. Any use of the information contained herein in any > way > > > > > (including, but not limited to, total or partial disclosure, > > > > reproduction, > > > > > or dissemination) by persons other than the intended recipient(s) > is > > > > > prohibited. If you receive this e-mail in error, please notify the > > > sender > > > > > by phone or email immediately and delete it! > > > > > > > > > > > > > > > -----Original Message----- > > > > > From: 吕文龙(吕文龙) [mailto:wenlong....@alibaba-inc.com] > > > > > Sent: Thursday, July 07, 2016 11:59 AM > > > > > To: dev@flink.apache.org > > > > > Subject: 答复: [DISCUSS] Enhance Window Evictor in Flink > > > > > > > > > > HI, > > > > > I think it is necessary to support sorted window, which can avoid > > > > scanning > > > > > all the elements of window while trying to evicting element, which > > may > > > > cost > > > > > many IO operations, such as querying DBs to get elements from > state. > > > > > What's more, when an window aggregation function is invertible, > such > > as > > > > > sum, which can be updated by adding or removing a single record, > > window > > > > > results can be incrementally calculated. In this kind of case, we > can > > > > > dramatically improve the performance of window aggregation, if > > evictor > > > > can > > > > > trigger update of window aggregation state by some mechanism. > > > > > > > > > > Best Wishes! > > > > > --- > > > > > wenlong.lwl > > > > > > > > > > -----邮件原件----- > > > > > 发件人: Aljoscha Krettek [mailto:aljos...@apache.org] > > > > > 发送时间: 2016年7月7日 17:32 > > > > > 收件人: dev@flink.apache.org > > > > > 主题: Re: [DISCUSS] Enhance Window Evictor in Flink > > > > > > > > > > Hi, > > > > > regarding "sorting the window by event time": I also considered > this > > > but > > > > > in the end I don't think it's necessary. Sorting is rather > expensive > > > and > > > > > making decisions based on the order of elements can be tricky. An > > > extreme > > > > > example of why this can be problematic is the case where all > elements > > > in > > > > > the window have the same timestamp. Now, if you decide to evict the > > > > first 5 > > > > > elements based on timestamp order you basically arbitrarily evict 5 > > > > > elements. I think the better solution for doing time-based eviction > > is > > > to > > > > > do one pass over the elements to get an overview of the timestamp > > > > > distribution, then do a second pass and evict elements based on > what > > > was > > > > > learned in the first pass. This has complexity 2*n compared to the > > > n*log > > > > n > > > > > (plus the work of actually deciding what to evict) of the sort > based > > > > > strategy. > > > > > > > > > > I might be wrong, though, and there could be a valid use-case not > > > covered > > > > > by the above idea. > > > > > > > > > > regarding Vishnu's other use case of evicting based on some > decision > > in > > > > the > > > > > WindowFunction: could this be solved by doing the check for the > > pattern > > > > in > > > > > the evictor itself instead of in the window function? I'm very > > hesitant > > > > to > > > > > introduce a coupling between the different components of the > > windowing > > > > > system, i.e. assigner, trigger, evictor and window function. The > > reason > > > > is > > > > > that using an evictor has a huge performance impact since the > system > > > > always > > > > > has to keep all elements and cannot to incremental aggregation of > > > window > > > > > results and I therefore don't want to put specific features > regarding > > > > > eviction into the other components. > > > > > > > > > > Cheers, > > > > > Aljoscha > > > > > > > > > > On Thu, 7 Jul 2016 at 10:00 Radu Tudoran <radu.tudo...@huawei.com> > > > > wrote: > > > > > > > > > > > Hi, > > > > > > > > > > > > I think the situation Vishnu raised is something that should be > > > > > accounted. > > > > > > It can happen indeed that you want to condition what you evict > from > > > > > > the window based on the result of the function to be applied. > > > > > > > > > > > > My 2 cents... > > > > > > I would suggest adding a list for the elements of the stream > where > > > you > > > > > > can MARK them to be delete. Alternatively the iterator can be > > > extended > > > > > > to have a function Iterator.markForEviction(int); These can be > made > > > > > > available also in the apply function. Moreover, we can use this > to > > > > > > extend the functionality such that you add MARKs either for > > eviction > > > > > > after the function has finished triggering or to be evicted in > the > > > next > > > > > iteration. > > > > > > > > > > > > > > > > > > Dr. Radu Tudoran > > > > > > Research Engineer - Big Data Expert > > > > > > IT R&D Division > > > > > > > > > > > > > > > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH > > > > > > European Research Center > > > > > > Riesstrasse 25, 80992 München > > > > > > > > > > > > E-mail: radu.tudo...@huawei.com > > > > > > Mobile: +49 15209084330 > > > > > > Telephone: +49 891588344173 > > > > > > > > > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH > > > > > > Hansaallee 205, 40549 Düsseldorf, Germany, www.huawei.com > > Registered > > > > > > Office: Düsseldorf, Register Court Düsseldorf, HRB 56063, > Managing > > > > > > Director: Bo PENG, Wanzhou MENG, Lifang CHEN Sitz der > Gesellschaft: > > > > > > Düsseldorf, Amtsgericht Düsseldorf, HRB 56063, > > > > > > Geschäftsführer: Bo PENG, Wanzhou MENG, Lifang CHEN This e-mail > and > > > > > > its attachments contain confidential information from HUAWEI, > which > > > is > > > > > > intended only for the person or entity whose address is listed > > above. > > > > > > Any use of the information contained herein in any way > (including, > > > but > > > > > > not limited to, total or partial disclosure, reproduction, or > > > > > > dissemination) by persons other than the intended recipient(s) is > > > > > > prohibited. If you receive this e-mail in error, please notify > the > > > > > > sender by phone or email immediately and delete it! > > > > > > > > > > > > -----Original Message----- > > > > > > From: Vishnu Viswanath [mailto:vishnu.viswanat...@gmail.com] > > > > > > Sent: Thursday, July 07, 2016 1:28 AM > > > > > > To: Dev > > > > > > Subject: Re: [DISCUSS] Enhance Window Evictor in Flink > > > > > > > > > > > > Thank you Maxim and Aljoscha. > > > > > > > > > > > > Yes the beforeEvict and afterEvict should able address point 3. > > > > > > > > > > > > I have one more use case in my mind (which I might have to do in > > the > > > > > > later stages of POC). > > > > > > What if the `evictAfter` should behave differently based on the > > > window > > > > > > function. > > > > > > > > > > > > For example. > > > > > > I have a window that got triggered and my evict function is being > > > > > > called after the apply function. In such cases I should be able > to > > > > > > decide on what I should evict based on the window function. > > > > > > e.g., > > > > > > let the window have elements of type `case class Item(id: String, > > > type: > > > > > > String)` and let the types be `type1` and `type2`. > > > > > > If window function is able to find a sequence : `type1 type2 > > type1`, > > > > > > then evict all elements of the type type2. > > > > > > or if the window function is able to find a sequence `type2 type2 > > > > > > type1`, then evict all elements of type type1 else don't evict > any > > > > > elements. > > > > > > > > > > > > Is this possible? or at least let the window function choose > > between > > > > > > two Evictor functions -(one for success case and one failure > case) > > > > > > > > > > > > @Maxim: > > > > > > regarding the sorted window, actually I wanted my elements to be > > > > > > sorted but not for the eviction but while applying the window > > > function > > > > > > (so thought this could be done easily). But it would be good to > > have > > > > > > the window sorted based on EventTime. > > > > > > > > > > > > > > > > > > Thanks and Regards, > > > > > > Vishnu Viswanath, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Wed, Jul 6, 2016 at 3:55 PM, Maxim <mfat...@gmail.com> wrote: > > > > > > > > > > > > > Actually for such evictor to be useful the window should be > > sorted > > > > > > > by some field, usually event time. What do you think about > adding > > > > > > > sorted window abstraction? > > > > > > > > > > > > > > On Wed, Jul 6, 2016 at 11:36 AM, Aljoscha Krettek > > > > > > > <aljos...@apache.org> > > > > > > > wrote: > > > > > > > > > > > > > > > @Maxim: That's perfect I didn't think about using > > > > > > > > Iterator.remove() for that. I'll update the doc. What do you > > > think > > > > > > > > Vishnu? This should also > > > > > > > cover > > > > > > > > your before/after case nicely. > > > > > > > > > > > > > > > > @Vishnu: The steps would be these: > > > > > > > > - Converge on a design in this discussion > > > > > > > > - Add a Jira issue here: > > > > > > > > https://issues.apache.org/jira/browse/FLINK > > > > > > > > - Work on the code an create a pull request on github > > > > > > > > > > > > > > > > The steps are also outlined here > > > > > > > > http://flink.apache.org/how-to-contribute.html and here > > > > > > > > http://flink.apache.org/contribute-code.html. > > > > > > > > > > > > > > > > - > > > > > > > > Aljoscha > > > > > > > > > > > > > > > > On Wed, 6 Jul 2016 at 19:45 Maxim <mfat...@gmail.com> wrote: > > > > > > > > > > > > > > > > > The new API forces iteration through every element of the > > > buffer > > > > > > > > > even > > > > > > > if > > > > > > > > a > > > > > > > > > single value to be evicted. What about implementing > > > > > > > > > Iterator.remove() method for elements? The API would look > > like: > > > > > > > > > > > > > > > > > > public interface Evictor<T, W extends Window> extends > > > > > > > > > Serializable { > > > > > > > > > > > > > > > > > > /** > > > > > > > > > * Optionally evicts elements. Called before windowing > > > > > function. > > > > > > > > > * > > > > > > > > > * @param elements The elements currently in the pane. > Use > > > > > > > > > Iterator.remove to evict. > > > > > > > > > * @param size The current number of elements in the > pane. > > > > > > > > > * @param window The {@link Window} > > > > > > > > > */ > > > > > > > > > void evictBefore(Iterable<T> elements, int size, > > > > > > > > > EvictorContext > > > > > > > ctx); > > > > > > > > > > > > > > > > > > /** > > > > > > > > > * Optionally evicts elements. Called after windowing > > > > function. > > > > > > > > > * > > > > > > > > > * @param elements The elements currently in the pane. > Use > > > > > > > > > Iterator.remove to evict. > > > > > > > > > * @param size The current number of elements in the > pane. > > > > > > > > > * @param window The {@link Window} > > > > > > > > > */ > > > > > > > > > void evictAfter(Iterable<T> elements, int size, > > > > > > > > > EvictorContext ctx); } > > > > > > > > > > > > > > > > > > Such API allows to abort iteration at any point and evict > > > > > > > > > elements in > > > > > > > any > > > > > > > > > order. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > Maxim. > > > > > > > > > > > > > > > > > > On Wed, Jul 6, 2016 at 9:04 AM, Vishnu Viswanath < > > > > > > > > > vishnu.viswanat...@gmail.com> wrote: > > > > > > > > > > > > > > > > > > > > Hi Aljoscha, > > > > > > > > > > > > > > > > > > > > Thanks. Yes the new interface seems to address points 1 > and > > > 2. > > > > > > > > > > of > > > > > > > > > > > > > > > > > > > > *1) I am having a use case where I have to create a > custom > > > > > > > > > > Evictor > > > > > > > that > > > > > > > > > > will evict elements from the window based on the value > > (e.g., > > > > > > > > > > if I > > > > > > > have > > > > > > > > > > elements are of case class Item(id: Int, type:String) > then > > > > > > > > > > evict > > > > > > > > elements > > > > > > > > > > that has type="a"). I believe this is not currently > > > possible.* > > > > > > > > > > *2) this is somewhat related to 1) where there should be > an > > > > > > > > > > option to > > > > > > > > > evict > > > > > > > > > > elements from anywhere in the window. not only from the > > > > > > > > > > beginning of > > > > > > > > the > > > > > > > > > > window. (e.g., apply the delta function to all elements > and > > > > > > > > > > remove > > > > > > > all > > > > > > > > > > those don't pass. I checked the code and evict method > just > > > > > > > > > > returns > > > > > > > the > > > > > > > > > > number of elements to be removed and processTriggerResult > > > just > > > > > > > > > > skips > > > > > > > > > those > > > > > > > > > > many elements from the beginning. * > > > > > > > > > > *3) Add an option to enables the user to decide if the > > > > > > > > > > eviction > > > > > > > should > > > > > > > > > > happen before the apply function or after the apply > > function. > > > > > > > Currently > > > > > > > > > it > > > > > > > > > > is before the apply function, but I have a use case > where I > > > > > > > > > > need to > > > > > > > > first > > > > > > > > > > apply the function and evict afterward.* > > > > > > > > > > > > > > > > > > > > I would be interested in contributing to the code base. > > > Please > > > > > > > > > > let me > > > > > > > > > know > > > > > > > > > > the steps. > > > > > > > > > > > > > > > > > > > > Thanks and Regards, > > > > > > > > > > Vishnu Viswanath > > > > > > > > > > > > > > > > > > > > On Wed, Jul 6, 2016 at 11:49 AM, Aljoscha Krettek < > > > > > > > aljos...@apache.org > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Hi, > > > > > > > > > > > as mentioned in the thread on improving the Windowing > > API I > > > > > > > > > > > also > > > > > > > > have a > > > > > > > > > > > design doc just for improving WindowEvictors. I had > this > > in > > > > > > > > > > > my head > > > > > > > > for > > > > > > > > > a > > > > > > > > > > > while but was hesitant to publish but since people are > > > > > > > > > > > asking about > > > > > > > > > this > > > > > > > > > > > now might be a good time to post it. Here's the doc: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://docs.google.com/document/d/1Rr7xzlItYqvFXLyyy-Yv0vvw8f29QYAj > > > > > > > m5 > > > > > > > i9E4A_JlU/edit?usp=sharing > > > > > > > > > > > > > > > > > > > > > > Feedback/Suggestions are very welcome! Please let me > know > > > > > > > > > > > what you > > > > > > > > > think. > > > > > > > > > > > > > > > > > > > > > > @Vishnu: Are you interested in contributing a solution > > for > > > > > > > > > > > this to > > > > > > > > the > > > > > > > > > > > Flink code base? I'd be very happy to work with you on > > > this. > > > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > > Aljoscha > > > > > > > > > > > > > > > > > > > > > > P.S. I think it would be best to keep discussions to > the > > ML > > > > > > > > > > > because comments on the doc will not be visible here > for > > > > > > everyone. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
