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From "Jark Wu" <wuchong...@alibaba-inc.com>
Subject Re: [DISCUSS] Development of SQL OVER / Table API Row Windows for streaming tables
Date Tue, 24 Jan 2017 05:53:27 GMT
Hi Fabian, 

Thanks for bringing up this discussion and the nice approach to avoid overlapping contributions.

All of these make sense to me. But I have some questions.

Q1: If I understand correctly, we will not support TumbleRows and SessionRows at the beginning.
But maybe support them as a syntax sugar (in Table API) when the SlideRows is supported in
the future. Right ? 

Q2: How to support SessionRows based on SlideRows ?  I don't get how to partition on "gap-separated".

Q3: Should we break down the approach into smaller tasks for streaming tables and batch tables

Q4: The implementaion of SlideRows still need a custom operator that collects records in a
priority queue ordered by the "rowtime", which is similar to the design we discussed in FLINK-4697,

+1 not support for OVER ROW for event time at this point.

Regards, Jark

> 在 2017年1月24日,上午10:28,Hongyuhong <hongyuhong@huawei.com> 写道:
> Hi,
> We are also interested in streaming sql and very willing to participate and contribute.
> We are now in progress and we will also contribute to calcite to push forward the window
and stream-join support.
> --------------
> Sender: Fabian Hueske [mailto:fhueske@gmail.com] 
> Send Time: 2017年1月24日 5:55
> Receiver: dev@flink.apache.org
> Theme: Re: [DISCUSS] Development of SQL OVER / Table API Row Windows for streaming tables
> Hi Haohui,
> our plan was in fact to piggy-back on Calcite and use the TUMBLE function [1] once is
it is available (CALCITE-1345 [2]).
> Unfortunately, this issue does not seem to be very active, so I don't know what the progress
> I would suggest to move the discussion about group windows to a separate thread and keep
this one focused on the organization of the SQL OVER windows.
> Best,
> Fabian
> [1] http://calcite.apache.org/docs/stream.html)
> [2] https://issues.apache.org/jira/browse/CALCITE-1345
> 2017-01-23 22:42 GMT+01:00 Haohui Mai <ricetons@gmail.com>:
>> Hi Fabian,
>> FLINK-4692 has added the support for tumbling window and we are 
>> excited to try it out and expose it as a SQL construct.
>> Just curious -- what's your thought on the SQL syntax on tumbling window?
>> Implementation wise it might make sense to think tumbling window as a 
>> special case of the sliding window.
>> The problem I see is that the OVER construct might be insufficient to 
>> support all the use cases of tumbling windows. For example, it fails 
>> to express tumbling windows that have fractional time units (as 
>> pointed out in http://calcite.apache.org/docs/stream.html).
>> It looks to me that the Calcite / Azure Stream Analytics have 
>> introduced a new construct (TUMBLE / TUMBLINGWINDOW) to address this issue.
>> Do you think it is a good idea to follow the same conventions? Your 
>> ideas are appreciated.
>> Regards,
>> Haohui
>> On Mon, Jan 23, 2017 at 1:02 PM Haohui Mai <ricetons@gmail.com> wrote:
>>> +1
>>> We are also quite interested in these features and would love to 
>>> participate and contribute.
>>> ~Haohui
>>> On Mon, Jan 23, 2017 at 7:31 AM Fabian Hueske <fhueske@gmail.com> wrote:
>>>> Hi everybody,
>>>> it seems that currently several contributors are working on new 
>>>> features for the streaming Table API / SQL around row windows (as 
>>>> defined in
>>>> FLIP-11
>>>> [1]) and SQL OVER-style window (FLINK-4678, FLINK-4679, FLINK-4680, 
>>>> FLINK-5584).
>>>> Since these efforts overlap quite a bit I spent some time thinking 
>>>> about how we can approach these features and how to avoid 
>>>> overlapping contributions.
>>>> The challenge here is the following. Some of the Table API row 
>>>> windows
>> as
>>>> defined by FLIP-11 [1] are basically SQL OVER windows while other 
>>>> cannot be easily expressed as such (TumbleRows for row-count 
>>>> intervals, SessionRows).
>>>> However, since Calcite already supports SQL OVER windows, we can 
>>>> reuse
>> the
>>>> optimization logic for some of the Table API row windows. I also 
>>>> thought about the semantics of the TumbleRows and SessionRows 
>>>> windows as defined in
>>>> FLIP-11 and came to the conclusion that these are not well defined 
>>>> in
>>>> FLIP-11 and should rather be defined as SlideRows windows with a 
>>>> special PARTITION BY clause.
>>>> I propose to approach SQL OVER windows and Table API row windows as
>>>> follows:
>>>> We start with three simple cases for SQL OVER windows (not Table 
>>>> API
>> yet):
>>>> * OVER RANGE for event time
>>>> * OVER RANGE for processing time
>>>> * OVER ROW for processing time
>>>> All cases fulfill the following restrictions:
>>>> - All aggregations in SELECT must refer to the same window.
>>>> - PARTITION BY may not contain the rowtime attribute.
>>>> - ORDER BY must be on rowtime attribute (for event time) or on a 
>>>> marker function that indicates processing time. Additional sort 
>>>> attributes are not supported initially.
>>>> PRECEDING AND CURRENT ROW" are supported.
>>>> OVER ROW for event time cannot be easily supported. With event 
>>>> time, we may have late records which need to be injected into the 
>>>> order of records.
>>>> When
>>>> a record in injected in to the order where a row-count window has
>> already
>>>> been computed, this and all following windows will change. We could
>> either
>>>> drop the record or sent out many retraction records. I think it is 
>>>> best
>> to
>>>> not open this can of worms at this point.
>>>> The rational for all of the above restrictions is to have first 
>>>> versions of OVER windows soon.
>>>> Once we have the above cases covered we can extend and remove
>> limitations
>>>> as follows:
>>>> - Table API SlideRow windows (with the same restrictions as above). 
>>>> This will be mostly API work since the execution part has been solved before.
>>>> - Add support for FOLLOWING (except UNBOUNDED FOLLOWING)
>>>> - Add support for different windows in SELECT. All windows must be 
>>>> partitioned and ordered in the same way.
>>>> - Add support for additional ORDER BY attributes (besides time).
>>>> As I said before, TumbleRows and SessionRows windows as in FLIP-11 
>>>> are
>> not
>>>> well defined, IMO.
>>>> They can be expressed as SlideRows windows with special 
>>>> partitioning (partitioning on fixed, non-overlapping time ranges 
>>>> for TumbleRows, and gap-separated, non-overlapping time ranges for 
>>>> SessionRows) I would not start to work on those yet.
>>>> I would like to close all related JIRA issues (FLINK-4678, 
>>>> FLINK-4679, FLINK-4680, FLINK-5584) and restructure the development 
>>>> of these
>> features
>>>> as outlined above with corresponding JIRA issues.
>>>> What do others think? (I cc'ed the contributors assigned to the 
>>>> above
>>>> issues)
>>>> Best, Fabian
>>>> [1]
>>>> https://cwiki.apache.org/confluence/display/FLINK/FLIP-
>> 11%3A+Table+API+Stream+Aggregations

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