+1 to add `finish()` method to `TableFunction` only. Can we use `endInput` just like `BoundedOneInput`?
Best, Jingsong On Fri, Sep 16, 2022 at 11:54 PM Lincoln Lee <lincoln.8...@gmail.com> wrote: > > Hi Dawid, Piotr, > Agree with you that add finish() method to `TableFunction` only. Other > `UserDefinedFunction`s (`ScalarFunction`, `AggregateFunction`, > `AggregateTableFunction`) are not necessarily to have the finish > method(they can not emit records in legacy close() method). > > A `TableFunction` is used to correlate with the left table/stream, the > following example shows a case that user only select columns from the > correlated 'FeatureTF' (no left table column was selected): > ``` > SELECT feature1, feature2, feature3 > FROM MyTable t1 > JOIN LATERAL TABLE(FeatureTF(t1.f0, t1.f1)) AS F(feature1, feature2, > feature3) ON TRUE > ``` > the 'FeatureTF' can do some flushing work in legacy close() method and this > doesn't break any sql semantics, so I don't see any reason that we can > enforce users not do flushing work in new finish() method. I've updated the > flip doc to limit the change only for `TableFunction`[1]. > > For the more powerful `ProcessFunction`, I'd like to share some thoughts: > There indeed exists requirements for advanced usage in Table/SQL, even a > further UD-Operator, e.g., UD-Join for user controlled join logic which can > not simply expressed by SQL. This is an interesting topic, expect more > discussions on this. > > > [1] > https://cwiki.apache.org/confluence/display/FLINK/FLIP-260%3A+Expose+Finish+Method+For+TableFunction > > Best, > Lincoln Lee > > > Piotr Nowojski <pnowoj...@apache.org> 于2022年9月15日周四 22:39写道： > > > Hi Dawid, Lincoln, > > > > I would tend to agree with Dawid. It seems to me like `TableFunction` is > > the one that needs to be taken care of. Other types of > > `UserDefinedFunction` wouldn't be able to emit anything from the `finish()` > > even if we added it. And if we added `finish(Collector<T> out)` to them, it > > would create the same problems (how to pass the output type) that prevented > > us from adding `finish()` to all functions in the DataStream API. > > > > However I'm not sure what should be the long term solution for the Table > > API. For the DataStream API we wanted to provide a new, better and more > > powerful `ProcessFunction` for all of the unusual use cases, that currently > > require the use of `StreamOperator` API instead of `DataStream` functions. > > I don't know what would be an alternative in the Table API. > > > > Dawid, who do you think we should ping from the Table API/SQL teams to chip > > in? > > > > Best, > > Piotrek > > > > czw., 15 wrz 2022 o 12:38 Dawid Wysakowicz <dwysakow...@apache.org> > > napisał(a): > > > > > Hey Lincoln, > > > > > > Thanks for opening the discussion. > > > > > > To be honest I am not convinced if emitting from close there is a > > > contract that was envisioned and thus should be maintained. As far as I > > > can see it does affect only the TableFunction, because it has the > > > collect method. None of the other UDFs (ScalarFunction, > > > AggregateFunction) have means to emit records from close(). > > > > > > To be honest I am not sure what would be the consequences of interplay > > > with other operators which expect TableFunction to emit only when eval > > > is called. Not sure if there are such. > > > > > > If it is a thing that we are certain we want to support, I'd be much > > > more comfortable adding finish() to the TableFunction instead. Would be > > > happy to hear opinions from the Table API folks. > > > > > > Best, > > > > > > Dawid > > > > > > On 14/09/2022 15:55, Lincoln Lee wrote: > > > > Thanks @Piort for your valuable inputs! > > > > > > > > I did a quick read of the previous discussion you mentioned, seems my > > > flip > > > > title doesn't give a clear scope here and make some confusions, if my > > > > understanding is correct, the UDFs in your context is the user > > > > implemented `org.apache.flink.api.common.functions.Function`s, while > > the > > > > `UserDefinedFunction` I mentioned in the flip is limited to the > > > flink-table > > > > module which located in `org.apache.flink.table.functions`. > > > > > > > > Here's an use case we've met recently (which is indeed the motivation > > to > > > > propose this): > > > > one of our user implemented a > > > > `org.apache.flink.table.functions.TableFunction`, the simplified > > > > pseudo-code is as below: > > > > > > > > ``` > > > > class XFunction extend TableFunction<Out> { > > > > > > > > open(FunctionContext context){ > > > > initMemQueue(); > > > > initPythonProc() > > > > } > > > > > > > > eval(In in){ > > > > queue.offer(data) > > > > Out out = queue.poll() > > > > if (out != null) { > > > > collect(out) > > > > } > > > > } > > > > > > > > close(){ > > > > waitForPythonFinish() > > > > List<Out> outputs = drainQueue() > > > > outputs.foreach(out -> collect(out)) > > > > } > > > > } > > > > ``` > > > > It works well in lower flink versions until they attempt to do a > > upgrade > > > > recently, the 'flush' logic in the legacy close method of > > `TableFunction` > > > > cannot work properly any more. > > > > > > > > Before proposing the flip, I also considered the `flush()` extension on > > > the > > > > `org.apache.flink.api.common.functions.Function`, because some sql > > > > operators are also related, but currently not included in the scope of > > > this > > > > flip, maybe we can discuss it in another thread. > > > > > > > > Wish this helps explaining the reason and welcome your comments here! > > > > > > > > Best, > > > > Lincoln Lee > > > > > > > > > > > > Piotr Nowojski <pnowoj...@apache.org> 于2022年9月14日周三 16:56写道： > > > > > > > >> Hi Lincoln, > > > >> > > > >> Thanks for the proposal. Have you seen the old discussion about adding > > > this > > > >> `finish()` method? [1] We didn't add it to UDFs, as we didn't see a > > > >> motivation (maybe we have missed something), and at the same time it > > > wasn't > > > >> that easy. Plain `finish()` wouldn't be enough. Users would need a way > > > to > > > >> output records from the `finish()` call, so it would have to be typed > > > with > > > >> the user record (`finish(Collector<T> output)`). On the other hand, we > > > >> couldn't find an example where a user would actually need the > > `finish()` > > > >> call in an UDF, as it seemed to us it makes only sense for > > > >> operators/functions that are buffering records. Note back then, during > > > the > > > >> discussion, we were referring to this method as `flush()` or > > `drain()`. > > > >> > > > >> Can you shed some more light and provide more details on the exact > > > >> motivating example behind this proposal? > > > >> > > > >> Best, > > > >> Piotrek > > > >> > > > >> [1] https://lists.apache.org/thread/gmr9r3n3ktojt4bhoxz4t8qho6h7d1rp > > > >> > > > >> śr., 14 wrz 2022 o 08:22 Lincoln Lee <lincoln.8...@gmail.com> > > > napisał(a): > > > >> > > > >>> Hello everyone, > > > >>> > > > >>> I’d like to open a discussion on FLIP-260[1]: expose finish method > > > for > > > >>> UserDefinedFunction, this makes a chance for users who rely on finish > > > >> logic > > > >>> in the legacy close() method (< 1.14) to migrate to the new finish() > > > >>> method. > > > >>> > > > >>> The task lifecycle was changed in FLINK-22972[2]: a new finish() > > > phase > > > >>> was introduced (extracted the ‘finish’ part out of the ‘close’) and > > > >> removed > > > >>> the dispose() method. This change was also done in table module > > (e.g., > > > >>> `AbstractMapBundleOperator` for mini-batch operation ) but not > > covered > > > >> the > > > >>> UserDefinedFunction which only exposes open() and close() api for > > > custom > > > >>> usage, those customers who rely on the legacy close() api may > > encounter > > > >>> wrong result or suffer runtime errors after upgrading to the new > > > version. > > > >>> Strictly speaking, it is a bug caused by the breaking change, but due > > > to > > > >>> the public api change, we propose this flip. > > > >>> > > > >>> Looking forward to your comments or feedback. > > > >>> > > > >>> [1] > > > >>> > > > >>> > > > >> > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-260%3A+Expose+Finish+Method+For+UserDefinedFunction > > > >>> [2] https://issues.apache.org/jira/browse/FLINK-22972 > > > >>> > > > >>> Best, > > > >>> Lincoln Lee > > > >>> > > > > >
