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From Timo Walther <twal...@apache.org>
Subject Re: [DISCUSS] Table API / SQL indicators for event and processing time
Date Wed, 01 Mar 2017 09:06:55 GMT
Hi SunJincheng,

our basic idea was to let the underlying API extract and handle time 
correctly. Extracting timestamps and assigning watermarks is a serious 
business. More advanced users can create TableSources and define time 
there (using DataStream API) and less advanced users can simply use it.

Just for clarification: 't.rowtime does not extract anything. It just 
gives an alias to the metadata timestamp that is attached to each 
record, so that this metadata can be referenced and accessed using a 
ProcessFunction in future. Queries and subqueries always use the 
metadata timestamp for time-based calculation.

With the new design we reduce the difference of batch and stream. If you 
do 'long.rowtime, the column "long" will not be read but a reference to 
the metadata timestamp in streaming, in batch it will be read and has to 
be column that exists.

.window (Tumble over 2.rows on 'long as 'w) means the same in batch and 
streaming.

I think a first PoC prototype will help. I hope I can finish it until 
next week.

Regards,
Timo

Am 01/03/17 um 07:55 schrieb jincheng sun:
> Hi,Fabian,
>
>   Thanks for your attention to this discussion. Let me share some ideas
> about this. :)
>
> 1. Yes, the solution I have proposed can indeed be extended to support
> multi-watermarks. A single watermark is a special case of multiple
> watermarks (n = 1). I agree that for the realization of the simple, that we
> currently only support single watermark. Our idea is consistent.
>
>    BTW. I think even if we only use one attribute to generate watermark we
> also need to sort, because in OVER window(Event-time) we must know the
> exact data order, is that right?
>
> 2. I think our difference is how to register the watermark?
>     Now we see two ways:
>     A. t.rowtime;
>         If I understand correctly, in the current design when we use the
> expression 'rowtime, The system defaults based on user data to export
> timestamps;
>     B. registeredWatermarks ('t, waterMarkFunction1):
>         We are explicitly registered to generate watermarks and extract
> timestamps in user-defined ways;
>
>    These two ways are characterized by:
>     Approach A: The system defaults to export the value of the t field as a
> timestamp, which is simple for the system.
>     Approach B: the user can develop the logic of the export timestamp, for
> the user has been very flexible. For example: the field `t` is a complex
> field (value is:` xxx # 20170302111129 # yyy`), the user can press a
> certain logic export timestamp (20170302111129).
>
>     So i tend to approach B. What do you think?
>
>   3. We are very concerned about the unity of Stream and Batch, such as the
> current TableAPI:
>      Batch:
>       Table
>        .window (Tumble over 2.rows on 'long as' w) //' long is the normal
> field
>        .groupBy ('w)
>        .select ('int.count)
>
>      Stream:
>       Table
>        .window (Tumble over 5.milli on 'rowtime as' w) //' rowtime is the
> keyword
>        .groupBy ('w)
>        .select ('int.count)
>
>     As mentioned above, the two example are event-time aggregation window,
> but the writing did not do the same way, batch we have a specific column,
> stream need 'rowtime keyword. I think we need to try to eliminate this
> difference. What do you think?
>
>     In the current google doc I see `table.window (tumble over 1.hour on 't
> as' w) .groupBy ('a,' w) .select ('w.start,' b.count)`, Does this mean that
> in FLINK-5884 will remove the tableAPI 'rowtime keyword?
>
>    So I am currently talking on the event-time in the SQL indicators, in the
> table registered column attributes, does this mean that the batch and
> stream SQL in the writing and use of the same?
>
> Very appreciated for your feedback.
>
> Best,
> SunJincheng
>
> 2017-03-01 10:40 GMT+08:00 Xingcan Cui <xingcanc@gmail.com>:
>
>> Hi all,
>>
>> I have a question about the designate time for `rowtime`. The current
>> design do this during the DataStream to Table conversion. Does this mean
>> that `rowtime` is only valid for the source streams and can not be
>> designated after a subquery? (That's why I considered using alias to
>> dynamically designate it in a SQL before)
>>
>> Best,
>> Xingcan
>>
>> On Wed, Mar 1, 2017 at 5:35 AM, Fabian Hueske <fhueske@gmail.com> wrote:
>>
>>> Hi Jincheng Sun,
>>>
>>> registering watermark functions for different attributes to allow each of
>>> them to be used in a window is an interesting idea.
>>>
>>> However, watermarks only work well if the streaming data is (almost) in
>>> timestamp order. Since it is not possible to sort a stream, all
>> attributes
>>> that would qualify as event-time attributes need to be in almost the same
>>> order. I think this limits the benefits of having multiple watermark
>>> functions quite significantly. But maybe you have a good use case that
>> you
>>> can share where multiple event-time attributes would work well.
>>>
>>> So far our approach has been that a DataStream which is converted into a
>>> Table has already timestamps and watermarks assigned. We also assumed
>> that
>>> a StreamTableSource would provide watermarks and timestamps and indicate
>>> the name of the attribute that carries the timestamp.
>>>
>>> @Stefano: That's great news. I'd suggest to open a pull request and have
>> a
>>> look at PR #3397 which handles the (partitioned) unbounded case. Would be
>>> good to share some code between these approaches.
>>>
>>> Thanks, Fabian
>>>
>>> 2017-02-28 18:17 GMT+01:00 Stefano Bortoli <stefano.bortoli@huawei.com>:
>>>
>>>> Hi all,
>>>>
>>>> I have completed a first implementation that works for the SQL query
>>>> SELECT a, SUM(b) OVER (PARTITION BY c ORDER BY a RANGE BETWEEN 2
>>>> PRECEDING) AS sumB FROM MyTable
>>>>
>>>> I have SUM, MAX, MIN, AVG, COUNT implemented but I could test it just
>> on
>>>> simple queries such as the one above. Is there any specific case I
>> should
>>>> be looking at?
>>>>
>>>> Regards,
>>>> Stefano
>>>>
>>>> -----Original Message-----
>>>> From: jincheng sun [mailto:sunjincheng121@gmail.com]
>>>> Sent: Tuesday, February 28, 2017 12:26 PM
>>>> To: dev@flink.apache.org
>>>> Subject: Re: [DISCUSS] Table API / SQL indicators for event and
>>> processing
>>>> time
>>>>
>>>> Hi everyone, thanks for sharing your thoughts. I really like Timo’s
>>>> proposal, and I have a few thoughts want to share.
>>>>
>>>> We want to keep the query same for batch and streaming. IMO. “process
>>> time”
>>>> is something special to dataStream while it is not a well defined term
>>> for
>>>> batch query. So it is kind of free to create something new for
>>> processTime.
>>>> I think it is a good idea to add a proctime as a reserved keyword for
>>> SQL.
>>>>   Regarding to “event time”, it is well defined for batch query. So IMO,
>>> we
>>>> should keep the way of defining a streaming window exactly same as
>> batch
>>>> window. Therefore, the row for event time is nothing special, but just
>> a
>>>> normal column. The major difference between batch and stream is that in
>>>> dataStream the event time column must be associated with a watermark
>>>> function. I really like the way Timo proposed, that we can select any
>>>> column as rowtime. But I think instead of just clarify a column is a
>>>> rowtime (actually I do not think we need this special rowtime keyword),
>>> it
>>>> is better to register/associate the waterMark function to this column
>>> when
>>>> creating the table. For dataStream, we will validate a rowtime column
>>> only
>>>> if it has been associated with the waterMark function. A prototype code
>>> to
>>>> explain how it looks like is shown as below:
>>>>
>>>>    TableAPI:
>>>>       toTable(tEnv, 'a, 'b, 'c)
>>>>        .registeredWatermarks('a, waterMarkFunction1)
>>>>
>>>>       batchOrStreamTable
>>>>        .window(Tumble over 5.milli on 'a as 'w)
>>>>        .groupBy('w, 'b)
>>>>        .select('b, 'a.count as cnt1, 'c.sum as cnt2)
>>>>
>>>>    SQL:
>>>>      addTable[(Int, String, Long)]("MyTable", 'a, 'b, 'c)
>>>>        .registeredWatermarks('a, waterMarkFunction1)
>>>>
>>>>      SELECT a, SUM(b) OVER (PARTITION BY c ORDER BY a RANGE BETWEEN 2
>>>> PRECEDING) AS sumB FROM MyTable
>>>>
>>>> What do you think ?
>>>>
>>>> 2017-02-22 23:44 GMT+08:00 Timo Walther <twalthr@apache.org>:
>>>>
>>>>> Hi everyone,
>>>>>
>>>>> I have create an issue [1] to track the progress of this topic. I
>> have
>>>>> written a little design document [2] how we could implement the
>>>>> indicators and which parts have to be touched. I would suggest to
>>>>> implement a prototype, also to see what is possible and can be
>>>>> integrated both in Flink and Calcite. Feedback is welcome.
>>>>>
>>>>> Regards,
>>>>> Timo
>>>>>
>>>>> [1] https://issues.apache.org/jira/browse/FLINK-5884
>>>>> [2] https://docs.google.com/document/d/1JRXm09x_wKst6z6UXdCGF9tg
>>>>> F1ueOAsFiQwahR72vbc/edit?usp=sharing
>>>>>
>>>>>
>>>>>
>>>>> Am 21/02/17 um 15:06 schrieb Fabian Hueske:
>>>>>
>>>>> Hi Xingcan,
>>>>>> thanks for your thoughts.
>>>>>> In principle you are right that the monotone attribute property
>> would
>>>>>> be sufficient, however there are more aspects to consider than that.
>>>>>>
>>>>>> Flink is a parallel stream processor engine which means that data is
>>>>>> processed in separate processes and shuffle across them.
>>>>>> Maintaining a strict order when merging parallel streams would be
>>>>>> prohibitively expensive.
>>>>>> Flink's watermark mechanism helps operators to deal with
>> out-of-order
>>>>>> data (due to out-of-order input or shuffles).
>>>>>> I don't think we can separate the discussion about time attributes
>>>>>> from watermarks if we want to use Flink as a processing engine and
>>>>>> not reimplement large parts from scratch.
>>>>>>
>>>>>> When transforming a time attribute, we have to either align it with
>>>>>> existing watermarks or generate new watermarks.
>>>>>> If we want to allow all kinds of monotone transformations, we have
>> to
>>>>>> adapt the watermarks which is not trivial.
>>>>>> Instead, I think we should initially only allow very few monotone
>>>>>> transformations which are aligned with the existing watermarks. We
>>>>>> might later relax this condition if we see that users request this
>>>> feature.
>>>>>> You are right, that we need to track which attribute can be used as
>> a
>>>>>> time attribute (i.e., is increasing and guarded by watermarks).
>>>>>> For that we need to expose the time attribute when a Table is
>> created
>>>>>> (either when a DataStream is converted like: stream.toTable(tEnv,
>> 'a,
>>>>>> 'b,
>>>>>> 't.rowtime) or in a StreamTableSource) and track how it is used in
>>>>>> queries.
>>>>>> I am not sure if the monotone property would be the right choice
>>>>>> here, since data is only quasi-monotone and a monotone annotation
>>>>>> might trigger some invalid optimizations which change the semantics
>> of
>>>> a query.
>>>>>> Right now, Calcite does not offer a quasi-monotone property (at
>> least
>>>>>> I haven't found it).
>>>>>>
>>>>>> Best, Fabian
>>>>>>
>>>>>>
>>>>>> 2017-02-21 4:41 GMT+01:00 Xingcan Cui <xingcanc@gmail.com>:
>>>>>>
>>>>>> Hi all,
>>>>>>> As I said in another thread, the main difference between stream and
>>>>>>> table is that a stream is an ordered list while a table is an
>>>> unordered set.
>>>>>>> Without considering the out-of-order problem in practice, whether
>>>>>>> event-time or processing-time can be just taken as a monotonically
>>>>>>> increasing field and that's why the given query[1] would work. In
>>>>>>> other words, we must guarantee the "SELECT MAX(t22.rowtime) ..."
>>>>>>> subquery returns a single value that can be retrieved from the
>>>>>>> cached dynamic table since it's dangerous to join two un-windowed
>>>>>>> streams.
>>>>>>>
>>>>>>> Under this circumstance, I just consider adding a "monotonic
>>>>>>> hint"(INC or
>>>>>>> DEC) to the field of a (generalized) table (maybe using an
>>>>>>> annotation on the registerDataXX method) that can be used to
>>>>>>> indicate whether a field is monotonically increasing or decreasing.
>>>>>>> Then by taking rowtime as common (monotonically increasing) field,
>>>>>>> there are several benefits:
>>>>>>>
>>>>>>> 1) This can uniform the table and stream by importing total
>> ordering
>>>>>>> relation to an unordered set.
>>>>>>>
>>>>>>> 2) These fields can be modified arbitrarily as long as they keep
>> the
>>>>>>> declared monotonic feature and the watermark problem does not exist
>>>>>>> any more.
>>>>>>>
>>>>>>> 3) The monotonic hint will be useful in the query optimization
>>> process.
>>>>>>> What do you think?
>>>>>>>
>>>>>>> Best,
>>>>>>> Xingcan
>>>>>>>
>>>>>>> [1]
>>>>>>> SELECT​ ​t1.amount​,​ ​t2.rate
>>>>>>> FROM​ ​
>>>>>>>     table1 ​AS​ t1,
>>>>>>> ​ ​ table2 ​AS​ ​t2
>>>>>>> WHERE ​
>>>>>>>     t1.currency = t2.currency AND
>>>>>>>     t2.rowtime ​=​ ​(
>>>>>>> ​ ​​ ​  SELECT​ ​MAX(t22.rowtime)
>>>>>>> ​ ​​ ​  FROM​ ​table2 ​AS​ t22
>>>>>>> ​ ​​   ​AND​ ​t22.rowtime ​<=​ t1.rowtime)
>>>>>>>
>>>>>>> On Tue, Feb 21, 2017 at 2:52 AM, Fabian Hueske <fhueske@gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Hi everybody,
>>>>>>>> When Timo wrote to the Calcite mailing list, Julian Hyde replied
>>>>>>>> and gave good advice and explained why a system attribute for
>>>>>>>> event-time would be
>>>>>>>>
>>>>>>> a
>>>>>>>
>>>>>>>> problem [1].
>>>>>>>> I thought about this and agree with Julian.
>>>>>>>>
>>>>>>>> Here is a document to describe the problem, constraints in Flink
>>>>>>>> and a proposal how to handle processing time and event time in
>>>>>>>> Table API and
>>>>>>>>
>>>>>>> SQL:
>>>>>>>
>>>>>>>> ->
>>>>>>>> https://docs.google.com/document/d/1MDGViWA_
>>>>>>>>
>>>>>>> TCqpaVoWub7u_GY4PMFSbT8TuaNl-
>>>>>>>
>>>>>>>> EpbTHQ
>>>>>>>>
>>>>>>>> Please have a look, comment and ask questions.
>>>>>>>>
>>>>>>>> Thank you,
>>>>>>>> Fabian
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> https://lists.apache.org/thread.html/
>> 6397caf0ca37f97f2cd27d96f7a12c
>>>>>>>> 6fa845d6fd0870214fdce18d96@%3Cdev.calcite.apache.org%3E
>>>>>>>>
>>>>>>>> 2017-02-16 1:18 GMT+01:00 Fabian Hueske <fhueske@gmail.com>:
>>>>>>>>
>>>>>>>> Thanks everybody for the comments.
>>>>>>>>> Actually, I think we do not have much choice when deciding
>> whether
>>>>>>>>> to
>>>>>>>>>
>>>>>>>> use
>>>>>>>> attributes or functions.
>>>>>>>>> Consider the following join query:
>>>>>>>>>
>>>>>>>>> SELECT​ ​t1.amount​,​ ​t2.rate
>>>>>>>>> FROM​ ​
>>>>>>>>>     table1 ​AS​ t1,
>>>>>>>>> ​ ​ table2 ​AS​ ​t2
>>>>>>>>> WHERE ​
>>>>>>>>>     t1.currency = t2.currency AND
>>>>>>>>>     t2.rowtime ​=​ ​(
>>>>>>>>> ​ ​​ ​  SELECT​ ​MAX(t22.rowtime)
>>>>>>>>> ​ ​​ ​  FROM​ ​table2 ​AS​ t22
>>>>>>>>> ​ ​​   ​AND​ ​t22.rowtime ​<=​ t1.rowtime)
>>>>>>>>>
>>>>>>>>> The query joins two streaming tables. Table 1 is a streaming
>> table
>>>>>>>>> with amounts in a certain currency. Table 2 is a (slowly
>> changing)
>>>>>>>>> streaming table of currency exchange rates.
>>>>>>>>> We want to join the amounts stream with the exchange rate of the
>>>>>>>>> corresponding currency that is valid (i.e., last received value
>> ->
>>>>>>>>> MAX(rowtime)) at the rowtime of the amounts row.
>>>>>>>>> In order to specify the query, we need to refer to the rowtime of
>>>>>>>>> the different tables. Hence, we need a way to relate the rowtime
>>>>>>>>> expression
>>>>>>>>>
>>>>>>>> (or
>>>>>>>>
>>>>>>>>> marker) to a table.
>>>>>>>>> This is not possible with a parameterless scalar function.
>>>>>>>>>
>>>>>>>>> I'd like to comment on the concerns regarding the performance:
>>>>>>>>> In fact, the columns could be completely virtual and only exist
>>>>>>>>> during query parsing and validation.
>>>>>>>>> During execution, we can directly access the rowtime metadata of
>> a
>>>>>>>> Flink
>>>>>>>> streaming record (which is present anyway) or look up the current
>>>>>>>>> processing time from the machine clock. So the processing
>> overhead
>>>>>>>> would
>>>>>>>> actually be the same as with a marker function.
>>>>>>>>> Regarding the question on what should be allowed with a system
>>>>>>>>>
>>>>>>>> attribute:
>>>>>>>> IMO, it could be used as any other attribute. We need it at least
>>>>>>>> in
>>>>>>>> GROUP
>>>>>>>>
>>>>>>>>> BY, ORDER BY, and WHERE to define windows and joins. We could
>> also
>>>>>>>> allow
>>>>>>>> to
>>>>>>>>
>>>>>>>>> access it in SELECT if we want users to give access to rowtime
>> and
>>>>>>>>> processing time. So @Haohui, your query could be supported.
>>>>>>>>> However, what would not be allowed is to modify the value of the
>>>>>>>>> rows, i.e., by naming another column rowtime, i.e., "SELECT
>>>>>>>>> sometimestamp AS rowtime" would not be allowed, because Flink
>> does
>>>>>>>>> not support to modify
>>>>>>>>>
>>>>>>>> the
>>>>>>>>
>>>>>>>>> event time of a row (for good reasons) and processing time should
>>>>>>>>> not
>>>>>>>>>
>>>>>>>> be
>>>>>>>> modifiable anyway.
>>>>>>>>> @Timo:
>>>>>>>>> I think the approach to only use the system columns during
>> parsing
>>>>>>>>> and validation and converting them to expressions afterwards
>> makes
>>>>>>>>> a lot of sense.
>>>>>>>>> The question is how this approach could be nicely integrated with
>>>>>>>>>
>>>>>>>> Calcite.
>>>>>>>>
>>>>>>>>> Best, Fabian
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> 2017-02-15 16:50 GMT+01:00 Radu Tudoran <radu.tudoran@huawei.com
>>> :
>>>>>>>>> Hi,
>>>>>>>>>> My initial thought would be that it makes more sense to thave
>>>>>>>>>>
>>>>>>>>> procTime()
>>>>>>>> and rowTime() only as functions which in fact are to be used as
>>>>>>>>> markers.
>>>>>>>> Having the value (even from special system attributes does not
>> make
>>>>>>>>> sense
>>>>>>>>> in some scenario such as the ones for creating windows, e.g.,
>>>>>>>>>> If you have SELECT Count(*) OVER (ORDER BY procTime()...) If you
>>>>>>>>>> get the value of procTime you cannot do anything as you need
>>>>>>>>>>
>>>>>>>>> the
>>>>>>>> marker to know how to construct the window logic.
>>>>>>>>>> However, your final idea of having " implement some rule/logic
>>>>>>>>>> that translates the attributes to special RexNodes internally "
>> I
>>>>>>>>>> believe
>>>>>>>>>>
>>>>>>>>> is
>>>>>>>> good and gives a solution to both problems. One the one hand for
>>>>>>>> those
>>>>>>>>>> scenarios where you need the value you can access the value,
>>>>>>>>>> while for others you can see the special type of the RexNode and
>>>>>>>>>> use it as a
>>>>>>>>>>
>>>>>>>>> marker.
>>>>>>>>> Regarding keeping this data in a table...i am not sure as you
>>>>>>>>> would
>>>>>>>>> say
>>>>>>>> we  need to augment the data with two fields whether needed or
>>>>>>>>> not...this
>>>>>>>>> is nto necessary very efficient
>>>>>>>>>>
>>>>>>>>>> Dr. Radu Tudoran
>>>>>>>>>> Senior Research Engineer - Big Data Expert IT R&D Division
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> HUAWEI TECHNOLOGIES Duesseldorf GmbH
>>>>>>>>>> European Research Center
>>>>>>>>>> Riesstrasse 25, 80992 München
>>>>>>>>>>
>>>>>>>>>> E-mail: radu.tudoran@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: Timo Walther [mailto:twalthr@apache.org]
>>>>>>>>>> Sent: Wednesday, February 15, 2017 9:33 AM
>>>>>>>>>> To: dev@flink.apache.org
>>>>>>>>>> Subject: Re: [DISCUSS] Table API / SQL indicators for event and
>>>>>>>>>> processing time
>>>>>>>>>>
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> at first I also thought that built-in functions (rowtime() and
>>>>>>>>>> proctime()) are the easiest solution. However, I think to be
>>>>>>>>>>
>>>>>>>>> future-proof
>>>>>>>>> we should make them system attributes; esp. to relate them to a
>>>>>>>>>> corresponding table in case of multiple tables. Logically they
>> are
>>>>>>>>>> attributes of each row, which is already done in Table API.
>>>>>>>>>>
>>>>>>>>>> I will ask on the Calcite ML if there is a good way for
>>> integrating
>>>>>>>>>> system attributes. Right now, I would propose the following
>>>>>>>>>>
>>>>>>>>> implementation:
>>>>>>>>> - we introduce a custom row type (extending RelDataType)
>>>>>>>>>> - in a streaming environment every row has two attributes by
>>> default
>>>>>>>>>> (rowtime and proctime)
>>>>>>>>>> - we do not allow creating a row type with those attributes
>> (this
>>>>>>>>> should
>>>>>>>> already prevent `SELECT field AS rowtime FROM ...`)
>>>>>>>>>> - we need to ensure that these attributes are not part of
>>> expansion
>>>>>>>>> like
>>>>>>>> `SELECT * FROM ...`
>>>>>>>>>> - implement some rule/logic that translates the attributes to
>>>> special
>>>>>>>>>> RexNodes internally, such that the opimizer does not modify
>> these
>>>>>>>>> attributes
>>>>>>>>> What do you think?
>>>>>>>>>> Regards,
>>>>>>>>>> Timo
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Am 15/02/17 um 03:36 schrieb Xingcan Cui:
>>>>>>>>>>
>>>>>>>>>>> Hi all,
>>>>>>>>>>>
>>>>>>>>>>> thanks for this thread.
>>>>>>>>>>>
>>>>>>>>>>> @Fabian If I didn't miss the point, the main difference between
>>> the
>>>>>>>>>>> two approaches is whether or not taking these time attributes
>> as
>>>>>>>>>>> common table fields that are directly available to users.
>>> Whatever,
>>>>>>>>>>> these time attributes should be attached to records (right?),
>> and
>>>>>>>>>> the
>>>>>>>> discussion lies in whether give them public qualifiers like other
>>>>>>>>>>> common fields or private qualifiers and related get/set
>> methods.
>>>>>>>>>>> The former (system attributes) approach will be more compatible
>>>> with
>>>>>>>>>>> existing SQL read-only operations (e.g., select, join), but we
>>> need
>>>>>>>>>> to
>>>>>>>> add restrictions on SQL modification operation (like what?). I
>> think
>>>>>>>>>>> there are no needs to forbid users modifying these attributes
>> via
>>>>>>>>>>> table APIs (like map function). Just inform them about these
>>>> special
>>>>>>>>>>> attribute names like system built in aggregator names in
>>> iteration.
>>>>>>>>>>> As for the built in function approach, I don't know if, for
>> now,
>>>>>>>>>> there
>>>>>>>> are functions applied on a single row (maybe the value access
>>>>>>>>>>> functions like COMPOSITE.get(STRING)?). It seems that most of
>> the
>>>>>>>>>>> built in functions work for a single field or on columns and
>> thus
>>>> it
>>>>>>>>>>> will be mountains of work if we want to add a new kind of
>>> function
>>>>>>>>>> to
>>>>>>>> SQL. Maybe all existing operations should be modified to support
>> it.
>>>>>>>>>>> All in all, if there are existing supports for single row
>>> function,
>>>>>>>>>> I
>>>>>>>> prefer the built in function approach. Otherwise the system
>>>>>>>>>> attributes
>>>>>>>> approach should be better. After all there are not so much
>>>>>>>>>>> modification operations in SQL and maybe we can use alias to
>>>> support
>>>>>>>>>>> time attributes setting (just hypothesis, not sure if it's
>>>>>>>>>>>
>>>>>>>>>> feasible).
>>>>>>>> @Haohui I think the given query is valid if we add a aggregate
>>>>>>>>>>> function to (PROCTIME()
>>>>>>>>>>> - ROWTIME()) / 1000 and it should be executed efficiently.
>>>>>>>>>>>
>>>>>>>>>>> Best,
>>>>>>>>>>> Xingcan
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Feb 15, 2017 at 6:17 AM, Haohui Mai <
>> ricetons@gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>> Hi,
>>>>>>>>>>>> Thanks for starting the discussion. I can see there are
>> multiple
>>>>>>>>>>>> trade-offs in these two approaches. One question I have is
>> that
>>> to
>>>>>>>>>>>> which extent Flink wants to open its APIs to allow users to
>>> access
>>>>>>>>>>>> both processing and event time.
>>>>>>>>>>>>
>>>>>>>>>>>> Before we talk about joins, my understanding for the two
>>>> approaches
>>>>>>>>>>>> that you mentioned are essentially (1) treating the value of
>>> event
>>>>>>>>>>> /
>>>>>>>> processing time as first-class fields for each row, (2) limiting
>>>>>>>>>>> the
>>>>>>>> scope of time indicators to only specifying windows. Take the
>>>>>>>>>>>> following query as an
>>>>>>>>>>>> example:
>>>>>>>>>>>>
>>>>>>>>>>>> SELECT (PROCTIME() - ROWTIME()) / 1000 AS latency FROM table
>>> GROUP
>>>>>>>>>>> BY
>>>>>>>> FLOOR(PROCTIME() TO MINUTES)
>>>>>>>>>>>> There are several questions we can ask:
>>>>>>>>>>>>
>>>>>>>>>>>> (1) Is it a valid query?
>>>>>>>>>>>> (2) How efficient the query will be?
>>>>>>>>>>>>
>>>>>>>>>>>> For this query I can see arguments from both sides. I think at
>>> the
>>>>>>>>>>>> end of the day it really comes down to what Flink wants to
>>>> support.
>>>>>>>>>>>> After working on FLINK-5624 I'm more inclined to support the
>>>> second
>>>>>>>>>>>> approach (i.e., built-in functions). The main reason why is
>> that
>>>>>>>>>>> the
>>>>>>>> APIs of Flink are designed to separate times from the real
>>>>>>>>>>> payloads.
>>>>>>>> It probably makes sense for the Table / SQL APIs to have the same
>>>>>>>>>>> designs.
>>>>>>>>>>> For joins I don't have a clear answer on top of my head. Flink
>>>>>>>>>>>> requires two streams to be put in the same window before doing
>>> the
>>>>>>>>>>>> joins. This is essentially a subset of what SQL can express. I
>>>>>>>>>>>>
>>>>>>>>>>> don't
>>>>>>>> know what would be the best approach here.
>>>>>>>>>>>> Regards,
>>>>>>>>>>>> Haohui
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Feb 14, 2017 at 12:26 AM Fabian Hueske <
>>> fhueske@gmail.com
>>>>>>>>>>> wrote:
>>>>>>>>>>> Hi,
>>>>>>>>>>>>> It would as in the query I gave as an example before:
>>>>>>>>>>>>>
>>>>>>>>>>>>> SELECT
>>>>>>>>>>>>>      a,
>>>>>>>>>>>>>      SUM(b) OVER (PARTITION BY c ORDER BY proctime ROWS
>> BETWEEN
>>> 2
>>>>>>>>>>>>> PRECEDING AND CURRENT ROW) AS sumB, FROM myStream
>>>>>>>>>>>>>
>>>>>>>>>>>>> Here "proctime" would be a system attribute of the table
>>>>>>>>>>>>>
>>>>>>>>>>>> "myStream".
>>>>>>>> The table would also have another system attribute called
>>>>>>>>>>>> "rowtime"
>>>>>>>> which would be used to indicate event time semantics.
>>>>>>>>>>>>> These attributes would always be present in tables which are
>>>>>>>>>>>>>
>>>>>>>>>>>> derived
>>>>>>>> from streams.
>>>>>>>>>>>>> Because we still require that streams have timestamps and
>>>>>>>>>>>>>
>>>>>>>>>>>> watermarks
>>>>>>>> assigned (either by the StreamTableSource or the somewhere
>>>>>>>>>>>>> downstream the DataStream program) when they are converted
>>> into a
>>>>>>>>>>>>> table, there is no
>>>>>>>>>>>>>
>>>>>>>>>>>> need
>>>>>>>>>>>>
>>>>>>>>>>>>> to register anything.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Does that answer your questions?
>>>>>>>>>>>>>
>>>>>>>>>>>>> Best, Fabian
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> 2017-02-14 2:04 GMT+01:00 Radu Tudoran <
>>> radu.tudoran@huawei.com
>>>>> :
>>>>>>>>>>>>> Hi Fabian,
>>>>>>>>>>>>>> Thanks for starting the discussion. Before I give my
>> thoughts
>>> on
>>>>>>>>>>>>>> this
>>>>>>>>>>>>>>
>>>>>>>>>>>>> can
>>>>>>>>>>>>> you please give some examples of how would you see option of
>>>>>>>>>>>>> using
>>>>>>>> "system
>>>>>>>>>>>>>> attributes"?
>>>>>>>>>>>>>> Do you use this when you register the stream as a table, do
>>> you
>>>>>>>>>>>>> use
>>>>>>>> if when you call an SQL query, do you use it when you translate
>>>>>>>>>>>>>> back a
>>>>>>>>>>>>>>
>>>>>>>>>>>>> table
>>>>>>>>>>>>> to a stream / write it to a dynamic table?
>>>>>>>>>>>>>> Dr. Radu Tudoran
>>>>>>>>>>>>>> Senior Research Engineer - Big Data Expert IT R&D Division
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> HUAWEI TECHNOLOGIES Duesseldorf GmbH
>>>>>>>>>>>>>> European Research Center
>>>>>>>>>>>>>> Riesstrasse 25, 80992 München
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> E-mail: radu.tudoran@huawei.com
>>>>>>>>>>>>>> Mobile: +49 15209084330 <+49%201520%209084330>
>>>>>>>>>>>>>> Telephone: +49 891588344173 <+49%2089%201588344173>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> 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: Fabian Hueske [mailto:fhueske@gmail.com]
>>>>>>>>>>>>>> Sent: Tuesday, February 14, 2017 1:01 AM
>>>>>>>>>>>>>> To: dev@flink.apache.org
>>>>>>>>>>>>>> Subject: [DISCUSS] Table API / SQL indicators for event and
>>>>>>>>>>>>>>
>>>>>>>>>>>>> processing
>>>>>>>>>>> time
>>>>>>>>>>>>>> Hi,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I'd like to start an discussion about how Table API / SQL
>>>> queries
>>>>>>>>>>>>> indicate
>>>>>>>>>>>>>
>>>>>>>>>>>>>> whether an operation is done in event or processing time.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> 1) Why do we need to indicate the time mode?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> We need to distinguish event time and processing time mode
>> for
>>>>>>>>>>>>> operations
>>>>>>>>>>>>> in queries in order to have the semantics of a query fully
>>>>>>>>>>>>> defined.
>>>>>>>> This cannot be globally done in the TableEnvironment because some
>>>>>>>>>>>>> queries
>>>>>>>>>>>>> explicitly request an expression such as the ORDER BY clause
>> of
>>>>>>>>>>>>> an
>>>>>>>> OVER
>>>>>>>>>>> window with PRECEDING / FOLLOWING clauses.
>>>>>>>>>>>>>> So we need a way to specify something like the following
>>> query:
>>>>>>>>>>>>>> SELECT
>>>>>>>>>>>>>>      a,
>>>>>>>>>>>>>>      SUM(b) OVER (PARTITION BY c ORDER BY proctime ROWS
>>> BETWEEN 2
>>>>>>>>>>>>> PRECEDING
>>>>>>>>>>>>> AND CURRENT ROW) AS sumB, FROM myStream
>>>>>>>>>>>>>> where "proctime" indicates processing time. Equivalently
>>>>>>>>>>>>>>
>>>>>>>>>>>>> "rowtime"
>>>>>>>> would
>>>>>>>>>>>>> indicate event time.
>>>>>>>>>>>>>> 2) Current state
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> The current master branch implements time support only for
>>>>>>>>>>>>>>
>>>>>>>>>>>>> grouping
>>>>>>>> windows in the Table API.
>>>>>>>>>>>>>> Internally, the Table API converts a 'rowtime symbol (which
>>>> looks
>>>>>>>>>>>>> like
>>>>>>>>>>> a
>>>>>>>>>>>>> regular attribute) into a special expression which indicates
>>>>>>>>>>>>> event-time.
>>>>>>>>>>>>> For example:
>>>>>>>>>>>>>> table
>>>>>>>>>>>>>>      .window(Tumble over 5.milli on 'rowtime as 'w)
>>>>>>>>>>>>>>      .groupBy('a, 'w)
>>>>>>>>>>>>>>      .select(...)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> defines a tumbling event-time window.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Processing-time is indicated by omitting a time attribute
>>>>>>>>>>>>>> (table.window(Tumble over 5.milli as 'w) ).
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> 3) How can we do that in SQL?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> In SQL we cannot add special expressions without touching
>> the
>>>>>>>>>>>>> parser
>>>>>>>>> which
>>>>>>>>>>>>>> we don't want to do because we want to stick to the SQL
>>>> standard.
>>>>>>>>>>>>>> Therefore, I see only two options: adding system attributes
>> or
>>>>>>>>>>>>>> (parameterless) built-in functions. I list some pros and
>> cons
>>> of
>>>>>>>>>>>>> the
>>>>>>>>> approaches below:
>>>>>>>>>>>>>> 1. System Attributes:
>>>>>>>>>>>>>> + most natural way to access a property of a record.
>>>>>>>>>>>>>> + works with joins, because time attributes can be related
>> to
>>>>>>>>>>>>> tables
>>>>>>>>> - We need to ensure the attributes are not writable and always
>>>>>>>>>>>>> present
>>>>>>>>>>> in
>>>>>>>>>>>>> streaming tables (i.e., they should be system defined
>>>>>>>>>>>>> attributes).
>>>>>>>> - Need to adapt existing Table API expressions (will not change
>>>>>>>>>>>>> the
>>>>>>>> API
>>>>>>>>>>> but some parts of the internal translation)
>>>>>>>>>>>>>> - Event time value must be set when the stream is converted,
>>>>>>>>>>>>>>
>>>>>>>>>>>>> processing
>>>>>>>>>>> time is evaluated on the fly
>>>>>>>>>>>>>> 2. Built-in Functions
>>>>>>>>>>>>>> + Users could try to modify time attributes which is not
>>>> possible
>>>>>>>>>>>>> with
>>>>>>>>>>> functions
>>>>>>>>>>>>>> - do not work with joins, because we need to address
>> different
>>>>>>>>>>>>> relations
>>>>>>>>>>>>> - not a natural way to access a property of a record
>>>>>>>>>>>>>> I think the only viable choice are system attributes,
>> because
>>>>>>>>>>>>> built-in
>>>>>>>>>>> functions cannot be used for joins.
>>>>>>>>>>>>>> However, system attributes are the more complex solution
>>> because
>>>>>>>>>>>>> they
>>>>>>>>> need
>>>>>>>>>>>>>> a better integration with Calcite's SQL validator
>> (preventing
>>>>>>>>>>>>> user
>>>>>>>> attributes which are named rowtime for instance).
>>>>>>>>>>>>>> Since there are currently a several contributions on the way
>>>>>>>>>>>>>>
>>>>>>>>>>>>> (such
>>>>>>>> as
>>>>>>>>
>>>>>>>>> SQL
>>>>>>>>>>>>> OVER windows FLINK-5653 to FLINK-5658) that need time
>>> indicators,
>>>>>>>>>>>>> we
>>>>>>>>> need a
>>>>>>>>>>>>>> solution soon to be able to make progress.
>>>>>>>>>>>>>> There are two PRs, #3252 and #3271, which implement the
>>> built-in
>>>>>>>>>>>>> marker
>>>>>>>>>>> functions proctime() and rowtime() and which could serve as a
>>>>>>>>>>>>> temporary
>>>>>>>>>>> solution (since we do not work on joins yet).
>>>>>>>>>>>>>> I would like to suggest to use these functions as a starting
>>>>>>>>>>>>>>
>>>>>>>>>>>>> point
>>>>>>>> (once
>>>>>>>>>>>>> the PRs are merged) and later change to the system attribute
>>>>>>>>>>>>> solution
>>>>>>>>> which
>>>>>>>>>>>>>> needs a bit more time to be implemented.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I talked with Timo today about this issue and he said he
>> would
>>>>>>>>>>>>> like
>>>>>>>> to
>>>>>>>>>>> investigate how we can implement this as system functions
>>>>>>>>>>>>> properly
>>>>>>>> integrated with Calcite and the SQL Validator.
>>>>>>>>>>>>>> What do others think?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Best, Fabian
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>


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