Hi everyone, I just want to add that I was referring to NULL values not specifically to timefields but to the event itself. If you have the follow situation
Stream 1: .... | event1 | .... Stream 2: .... | | .... And you have a LEFT JOIN between stream 1 and stream 2 (no condition)...then you still need to emit (event1,null) ... as this is the behavior of left join. This is maybe a very simple situation, but the point is that left joins and right joins can have situation when you have elements only in the main stream and no element in the right stream. And for this case you still need to emit. Regarding whether time should be decided by system or not...i think the answer is it depends. I think the example from Jack is very good and shows the need for some mechanisms to select/manage the time (I like the proposal of having functions to insert the time in the output!). However, if a business analyst would write a query without explicit time management we still need to have some default behavior in the system. As per my initial proposal, I think we need to decide on one timestamp field to carry (either a new one at the moment of the join) or the timestamp from the main stream (...although I am not sure which one is the main stream in the case of a full join:) ) Dr. Radu Tudoran Staff Research Engineer - Big Data Expert IT R&D Division HUAWEI TECHNOLOGIES Duesseldorf GmbH German Research Center Munich Office 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, Qiuen Peng, Shengli Wang Sitz der Gesellschaft: Düsseldorf, Amtsgericht Düsseldorf, HRB 56063, Geschäftsführer: Bo PENG, Qiuen Peng, Shengli Wang 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: Jark Wu [mailto:j...@apache.org] Sent: Wednesday, July 26, 2017 8:29 AM To: dev@flink.apache.org Subject: Re: [DISCUSS] Table API / SQL internal timestamp handling Hi Xingcan, IMO, I don't think event-time of join results could be automatically decided by system. Considering batch tables, if users want a event time window aggregation after join, user must specify the time field explicitly (T1.rowtime or T2.rowtime or the computed result of them). So in the case of streaming tables, the system also can't automatically decide the time field for users. In regards to the question you asked, I think we don't need to change the watermark no matter we choose the left rowtime or right rowtime or the combination. Because the watermark has been aligned with the rowtime in the source. Maybe I'm wrong about this, please correct me if I'm missing something. What do you think? Regards, Jark 2017-07-26 11:24 GMT+08:00 Xingcan Cui <xingc...@gmail.com>: > Hi all, > > @Fabian, thanks for raising this. > > @Radu and Jark, personally I think the timestamp field is critical for > query processing and thus should be declared as (or supposed to be) > NOT NULL. In addition, I think the event-time semantic of the join > results should be automatically decided by the system, i.e., we do not > hand it over to users so to avoid some unpredictable assignment. > > Generally speaking, consolidating different time fields is possible > since all of them should ideally be monotonically increasing. From my > point of view, the problem lies in > (1) what's the relationship between the old and new watermarks. Shall > they be one-to-one mapping or the new watermarks could skip some > timestamps? And (2) who is in charge of emitting the blocked > watermarks, the operator or the process function? > > I'd like to hear from you. > > Best, > Xingcan > > > > On Wed, Jul 26, 2017 at 10:40 AM, Jark Wu <j...@apache.org> wrote: > > > Hi, > > > > Radu's concerns make sense to me, especially the null value > > timestamp and multi-proctime. > > > > I have also something in my mind. I would like to propose some time > > indicator built-in functions, e.g. ROW_TIME(Timestamp ts) will > > generate a event time logical attribute, PROC_TIME() will generate a > > processing time logical attribute. It is similar to TUMBLE_ROWTIME > > proposed in this PR https://github.com/apache/flink/pull/4199. These > > can be used in any queries, but there still can't be more than one > > rowtime attribute or more than one proctime attribute in a table schema. > > > > The both selected timestamp fields from a JOIN query will be > materialized. > > If someone needs further down the computation based on the event > > time, > they > > need to create a new time attribute using the ROW_TIME(...) > > function. And this can also solve the null timestamp problem in LEFT > > JOIN, because we > can > > use a user defined function to combine the two rowtimes and make the > result > > as the event time attribute, e.g. SELECT ROW_TIME(udf(T1.rowtime, > > T2.rowtime)) as rowtime FROM T1 JOIN T2 ... > > > > > > What do you think? > > > > > > 2017-07-25 23:48 GMT+08:00 Radu Tudoran <radu.tudo...@huawei.com>: > > > > > Hi, > > > > > > I think this is an interesting discussion and I would like to add > > > some issues and give some feedback. > > > > > > - For supporting the join we do not only need to think of the time > > > but also on the null values. For example if you have a LEFT (or > > > RIGHT) JOIN between items of 2 input streams, and the secondary > > > input is not > > available > > > you should still emit Row.of(event1, null)...as far as I know if > > > you > need > > > to serialize/deserialize null values to send them they do not > > > work. So > we > > > should include this scenario in the discussions -If we will have > > > multiple timestamp in an (output) event, one question > is > > > how to select afterwards which is the primary time field on which > > > to operate. When we describe a query we might be able to specify > > > (or we > get > > > this implicitly if we implement the carryon of the 2 timestamps) > Select > > > T1.rowtime, T2.rowtime ...but if the output of a query is the > > > input of > a > > > new processing pipeline, then, do we support generally also that > > > the > > input > > > has 2 time fields? ...how do we deal with the 2 input fields > > > (maybe I > am > > > missing something) further in the datastream pipeline that we > > > build > based > > > on the output? > > > - For the case of proctime - do we need to carry 2 proctimes (the > > > proctimes of the incoming events from each stream), or 1 proctime > > > (as > we > > > operate on proctime and the combination of the 2 inputs can be > considered > > > as a new event, the current proctime on the machine can be > > > considered > the > > > (proc)time reference for output event) or 3 proctimes (the 2 > > > proctimes > of > > > the input plus the proctime when the new event was created)? > > > -Similar with the point above, for even time (which I am > > > understanding > as > > > the time when the event was created...or do we understand them as > > > a > time > > > carry within the event?) - when we join 2 events and output an > > > event > that > > > is the result of the join - isn't this a new event detach from the > > > source\input events? ... I would tend to say it is a new event and > > > then > > as > > > for proctime the event time of the new event is the current time > > > when > > this > > > output event was created. If we would accept this hypothesis then > > > we > > would > > > not need the 2 time input fields to be carried/managed implicitly. > > > If someone needs further down the computation pipeline, then in > > > the query > > they > > > would be selected explicitly from the input stream and projected > > > in > some > > > fields to be carried (Select T1.rowtime as FormerTime1, T2.rowtime > > > as FormerTime2, .... JOIN T1, T2...)...but they would not have the > timestamp > > > logic > > > > > > ..my 2 cents > > > > > > > > > > > > > > > Dr. Radu Tudoran > > > Staff Research Engineer - Big Data Expert IT R&D Division > > > > > > > > > HUAWEI TECHNOLOGIES Duesseldorf GmbH > > > German Research Center > > > Munich Office > > > 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, Qiuen Peng, Shengli Wang > > > Sitz der Gesellschaft: Düsseldorf, Amtsgericht Düsseldorf, HRB 56063, > > > Geschäftsführer: Bo PENG, Qiuen Peng, Shengli Wang > > > 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: Fabian Hueske [mailto:fhue...@gmail.com] > > > Sent: Tuesday, July 25, 2017 4:22 PM > > > To: dev@flink.apache.org > > > Subject: [DISCUSS] Table API / SQL internal timestamp handling > > > > > > Hi everybody, > > > > > > I'd like to propose and discuss some changes in the way how the Table > API > > > / SQL internally handles timestamps. > > > > > > The Table API is implemented on top of the DataStream API. The > DataStream > > > API hides timestamps from users in order to ensure that timestamps and > > > watermarks are aligned. Instead users assign timestamps and watermarks > > once > > > (usually at the source or in a subsequent operator) and let the system > > > handle the timestamps from there on. Timestamps are stored in the > > timestamp > > > field of the StreamRecord which is a holder for the user record and the > > > timestamp. DataStream operators that depend on time (time-windows, > > process > > > function, ...) access the timestamp from the StreamRecord. > > > > > > In contrast to the DataSteam API, the Table API and SQL are aware of > the > > > semantics of a query. I.e., we can analyze how users access timestamps > > and > > > whether they are modified or not. Another difference is that the > > timestamp > > > must be part of the schema of a table in order to have correct query > > > semantics. > > > > > > The current design to handle timestamps is as follows. The Table API > > > stores timestamps in the timestamp field of the StreamRecord. > Therefore, > > > timestamps are detached from the remaining data which is stored in Row > > > objects. Hence, the physical representation of a row is different from > > its > > > logical representation. We introduced a translation layer (RowSchema) > to > > > convert logical schema into physical schema. This is necessery for > > > serialization or code generation when the logical plan is translated > > into a > > > physical execution plan. Processing-time timestamps are similarly > > handled. > > > They are not included in the physical schema and looked up when needed. > > > This design also requires that we need to materialize timestamps when > > they > > > are accessed by expressions. Timestamp materialization is done as a > > > pre-optimization step. > > > > > > While thinking about the implementation of the event-time windowed > > > stream-stream join [1] I stumbled over the question which timestamp of > > both > > > input tables to forward. With the current design, we could only have a > > > single timestamp, so keeping both timestamps would not be possible. The > > > choice of the timestamp would need to be specified by the query > otherwise > > > it would lack clear semantics. When executing the join, the join > operator > > > would need to make sure that no late data is emitted. This would only > > work > > > the operator was able to hold back watermarks [2]. > > > > > > With this information in mind, I'd like to discuss the following > > proposal: > > > > > > - We allow more than one event-time timestamp and store them directly > in > > > the Row > > > - The query operators ensure that the watermarks are always behind all > > > event-time timestamps. With additional analysis we will be able to > > restrict > > > this to timestamps that are actually used as such. > > > - When a DataStream operator is time-based (e.g., a DataStream > > > time-windows), we inject an operator that copies the timestamp from the > > Row > > > into the StreamRecord. > > > - We try to remove the distinction between logical and physical schema. > > > For event-time timestamps this is because we store them in the Row > > object, > > > for processing-time timestamps, we add a dummy byte field. When > > accessing a > > > field of this type, the code generator injects the code to fetch the > > > timestamps. > > > - We might be able to get around the pre-optimization time > > materialization > > > step. > > > - A join result would be able to keep both timestamps. The watermark > > would > > > be hold back for both so both could be used in subsequent operations. > > > > > > I admit, I haven't thought this completely through. > > > However, the benefits of this design from my point of view are: > > > - encoding of timestamps in Rows means that the logical schema is equal > > to > > > the physical schema > > > - no timestamp materialization > > > - support for multiple timestamps. Otherwise we would need to expose > > > internal restrictions to the user which are hard to explain / > > communicate. > > > - no need to change any public interfaces at the moment. > > > > > > The drawbacks as far as I see them are: > > > - additional payload due to unused timestamp field + possibly the > > > processing-time dummy field > > > - complete rework of the internal timestamp logic (again...) > > > > > > Please let me know what you think, > > > Fabian > > > > > > [1] https://issues.apache.org/jira/browse/FLINK-6233 > > > [2] https://issues.apache.org/jira/browse/FLINK-7245 > > > > > >
