Hi Jincheng, Thanks for the clarification. I think you just pointed out my concern by yourself:
> When a user uses a User-defined table aggregate function (UDTAGG), he must understand the behavior of the UDTAGG, including the return type and the characteristics of the returned data. such as the key fields. This indicates that the UDTAGG is somehow be classified to different types, one will no key, one with key information. So the developer of the UDTAGG should choose which type of this function should be. In this case, my question would be, why don't we have explicit information about keys such as we split UDTAGG to keyed UDTAGG and non-keyed UDTAGG. So the user and the framework will have a better understanding of this UDTAGG. `withKeys` solution is letting user to choose the key and it seems it will only work correctly only if the user choose the *right* key this UDTAGG has. Let me know if this makes sense to you. Best, Kurt On Thu, Jul 4, 2019 at 4:32 PM jincheng sun <sunjincheng...@gmail.com> wrote: > Hi All, > > @Kurt Young <ykt...@gmail.com> one user-defined table aggregate function > can be used in both with(out) keys case, and we do not introduce any other > aggregations. just like the explanation from @Hequn. > > @Hequn Cheng <chenghe...@gmail.com> thanks for your explanation! > > One thing should be mentioned here: > > When a user uses a User-defined table aggregate function (UDTAGG), he must > understand the behavior of the UDTAGG, including the return type and the > characteristics of the returned data. such as the key fields. So although > using `withKeys` approach it is not rigorous enough(we do not need) but > intuitive enough, considering that if `flatAggregate` is followed by an > `upsertSink`, then the user must know the keys of the output of UDTAGG > clearly, otherwise the keys of `upsertSink` cannot be defined. So I still > prefer the `withKeys` solution by now. > > Looking forward to any feedback from all of you! > > Best, > Jincheng > > > > Hequn Cheng <chenghe...@gmail.com> 于2019年7月1日周一 下午5:35写道： > >> Hi Kurt, >> >> Thanks for your questions. Here are my thoughts. >> >> > if I want to write such kind function, should I make sure that this >> function is used with some keys? >> The key information may not be used. We can also use RetractSink to emit >> the table directly. >> >> > If I need a use case to calculate topn without key, should I write >> another function or I can reuse previous one. >> For the TopN example, you can reuse the previous function if you don't >> care >> about the key information. >> >> So, the key information is only an indicator(or a description), not an >> operator, as Jincheng mentioned above. >> We do not need to change the function logic and it will not add any other >> aggregations. >> >> BTW, we have three approaches in the document. Approach 1 defines keys on >> API level as we think it's more common to define keys on Table. >> While approach 3 defines keys in the TableAggregateFunction which is more >> precise but it is not very clear for Table users. So, we should take all >> these into consideration, and make the decision in this discussion thread. >> >> You can take a look at the document and welcome any suggestions or other >> better solutions. >> >> Best, Hequn >> >> >> On Mon, Jul 1, 2019 at 12:13 PM Kurt Young <ykt...@gmail.com> wrote: >> >> > Hi Jincheng, >> > >> > Thanks for the clarification. Take 'TopN' for example, if I want to >> write >> > such kind function, >> > should I make sure that this function is used with some keys? If I need >> a >> > use case to calculate >> > topn without key, should I write another function or I can reuse >> previous >> > one. >> > >> > I'm not sure about the idea of this does not involve semantic changes. >> To >> > me, it sounds like >> > we are doing another nested aggregation inside the table >> > which TableAggregateFunction emits. >> > >> > Maybe I'm not familiar with this function enough, hope you can help me >> to >> > understand. >> > >> > Best, >> > Kurt >> > >> > >> > On Mon, Jul 1, 2019 at 11:59 AM jincheng sun <sunjincheng...@gmail.com> >> > wrote: >> > >> > > Hi Kurt, >> > > >> > > Thanks for your questions, I am glad to share my thoughts here: >> > > >> > > My question is, will that effect the logic ofTableAggregateFunction >> user >> > > > wrote? Should the user know that there will a key and make some >> changes >> > > to >> > > > this function? >> > > >> > > >> > > No, the keys information depends on the implementation of the >> > > TableAggregateFunction. >> > > For example, for a `topN` user defined TableAggregateFunction, we can >> > only >> > > use the `keys` if the `topN` contains `rankid` in the output. You can >> > > treat the >> > > `keys` like an indicator. >> > > >> > > If not, how will framework deal with the output of user's >> > > > TableAggregateFunction. if user output multiple rows with the same >> > key, >> > > > should be latter one replace previous ones? >> > > >> > > >> > > If a TableAggregateFunction outputs multiple rows with the same key, >> the >> > > latter one should replace the previous one, either with upsert mode or >> > > retract mode. i.e., Whether the user defines the Key or not, the Flink >> > > framework should ensure the correctness of the semantics. >> > > >> > > At present, the problem we are discussing does not involve semantic >> > > changes. The definition of keys is to support non-window >> flatAggregate on >> > > upsert mode. (The upsert mode is already supported in the flink >> > framework. >> > > The current discussion only needs to inform the framework that the >> keys >> > > information, which is the `withKeys` API we discussing.) >> > > >> > > Welcome any other feedbacks :) >> > > >> > > Best, >> > > Jincheng >> > > >> > > Kurt Young <ykt...@gmail.com> 于2019年7月1日周一 上午9:23写道： >> > > >> > > > Hi, >> > > > >> > > > I have a question about the key information of >> TableAggregateFunction. >> > > > IIUC, you need to define >> > > > something like primary key or unique key in the result table of >> > > > TableAggregateFunction, and also >> > > > need a way to let user configure this through the API. My question >> is, >> > > will >> > > > that effect the logic of >> > > > TableAggregateFunction user wrote? Should the user know that there >> > will a >> > > > key and make some changes >> > > > to this function? >> > > > >> > > > If so, what's the semantic the user should learned. If not, how will >> > > > framework deal with the output of user's >> > > > TableAggregateFunction. For example, if user output multiple rows >> with >> > > the >> > > > same key, should be latter one >> > > > replace previous ones? >> > > > >> > > > Best, >> > > > Kurt >> > > > >> > > > >> > > > On Mon, Jul 1, 2019 at 7:19 AM jincheng sun < >> sunjincheng...@gmail.com> >> > > > wrote: >> > > > >> > > > > Hi hequn, Thanks for the reply! I think `withKeys` solution is our >> > > better >> > > > > choice! >> > > > > >> > > > > >> > > > > Hequn Cheng <chenghe...@gmail.com> 于2019年6月26日周三 下午5:11写道： >> > > > > >> > > > > > Hi Jincheng, >> > > > > > >> > > > > > Thanks for raising the discussion! >> > > > > > The key information is very important for query optimizations. >> It >> > > would >> > > > > be >> > > > > > nice if we can use upsert mode to achieve better performance. >> > > > > > >> > > > > > +1 for the `withKeys` proposal. :) >> > > > > > >> > > > > > Best, Hequn >> > > > > > >> > > > > > >> > > > > > On Wed, Jun 26, 2019 at 4:37 PM jincheng sun < >> > > sunjincheng...@gmail.com >> > > > > >> > > > > > wrote: >> > > > > > >> > > > > > > Hi all, >> > > > > > > >> > > > > > > With the continuous efforts from the community, we already >> > > supported >> > > > > > > `flatAggregate`[1] on TableAPI in retract mode. I think It's >> > better >> > > > to >> > > > > > add >> > > > > > > upsert mode for `flatAggregate`. >> > > > > > > >> > > > > > > The result table of streaming non-window `flatAggregate` is a >> > table >> > > > > > > contains updates. We can, of course, use a >> > > RetractStreamTableSink[2] >> > > > to >> > > > > > > emit the table, but we can get better performance in upsert >> mode. >> > > > > > However, >> > > > > > > due to the lack of keys, we can’t use an >> UpsertStreamTableSink to >> > > > emit >> > > > > > the >> > > > > > > table. We don’t have this problem for a normal aggregate as it >> > > emits >> > > > a >> > > > > > > single row for each group, so the unique keys are exactly the >> > same >> > > > with >> > > > > > the >> > > > > > > group keys. While for a `flatAggregate`, its pretty difference >> > that >> > > > due >> > > > > > to >> > > > > > > emits multi rows(a “sub-table”) for a single group. To solve >> this >> > > > > > problem, >> > > > > > > we need to find a way to define keys on flatAggregate, so >> that we >> > > can >> > > > > > also >> > > > > > > use upsert sink to emit the result table after flatAggregate. >> > > > > > > >> > > > > > > So, Aljoscha, Hequn and I prepared a design document for how >> to >> > > > define >> > > > > > the >> > > > > > > update keys for `flatAggregate` in upsert mode. The detail >> can >> > be >> > > > > found >> > > > > > > here: >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> https://docs.google.com/document/d/183qHo8PDG-xserDi_AbGP6YX9aPY0rVr80p3O3Gyz6U/edit?usp=sharing >> > > > > > > >> > > > > > > I appreciate it if you can have look at the document and any >> > > comments >> > > > > are >> > > > > > > welcome! >> > > > > > > >> > > > > > > >> > > > > > > Best, >> > > > > > > >> > > > > > > Jincheng >> > > > > > > >> > > > > > > >> > > > > > > [1] >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=97552739 >> > > > > > > >> > > > > > > [2] >> > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> https://ci.apache.org/projects/flink/flink-docs-release-1.8/dev/table/sourceSinks.html#defining-a-streamtablesource >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > >> >
