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From Etienne Chauchot <>
Subject Re: What's the root cause of not supporting multiple aggregations in structured streaming?
Date Fri, 04 Sep 2020 08:55:35 GMT
Hi Jungtaek Lim,

Nice to hear from you again since last time we talked :) and congrats on 
becoming a Spark committer in the meantime ! (if I'm not mistaking you 
were not at the time)

I totally agree with what you're saying on merging structural parts of 
Spark without having a broader consensus. What I don't understand is why 
there is not more investment in SS. Especially because in another thread 
the community is discussing about deprecating the regular DStream 
streaming framework.

Is the orientation of Spark now mostly batch ?

PS: yeah I saw your update on the doc when I took a look at 3.0 preview 
2 searching for this particular feature. And regarding the workaround, 
I'm not sure it meets my needs as it will add delays and also may mess 
up with watermarks.


Etienne Chauchot

On 04/09/2020 08:06, Jungtaek Lim wrote:
> Unfortunately I don't see enough active committers working on 
> Structured Streaming; I don't expect major features/improvements can 
> be brought in this situation.
> Technically I can review and merge the PR on major improvements in SS, 
> but that depends on how huge the proposal is changing. If the proposal 
> brings conceptual change, being reviewed by a committer wouldn't still 
> be enough.
> So that's not due to the fact we think it's worthless. (That might be 
> only me though.) I'd understand as there's not much investment on SS. 
> There's also a known workaround for multiple aggregations (I've 
> documented in the SS guide doc, in "Limitation of global watermark" 
> section), though I totally agree the workaround is bad.
> On Tue, Sep 1, 2020 at 12:28 AM Etienne Chauchot < 
> <>> wrote:
>     Hi all,
>     I'm also very interested in this feature but the PR is open since
>     January 2019 and was not updated. It raised a design discussion
>     around watermarks and a design doc was written
>     (
>     We also commented this design but no matter what it seems that the
>     subject is still stale.
>     Is there any interest in the community in delivering this feature
>     or is it considered worthless ? If the latter, can you explain why ?
>     Best
>     Etienne
>     On 22/05/2019 03:38, 张万新 wrote:
>>     Thanks, I'll check it out.
>>     Arun Mahadevan < <>> 于
>>     2019年5月21日周二 01:31写道:
>>         Heres the proposal for supporting it in "append" mode -
>> You could see if
>>         it addresses your requirement and post your feedback in the PR.
>>         For "update" mode its going to be much harder to support this
>>         without first adding support for "retractions", otherwise we
>>         would end up with wrong results.
>>         - Arun
>>         On Mon, 20 May 2019 at 01:34, Gabor Somogyi
>>         <
>>         <>> wrote:
>>             There is PR for this but not yet merged.
>>             On Mon, May 20, 2019 at 10:13 AM 张万新
>>             < <>>
>>             wrote:
>>                 Hi there,
>>                 I'd like to know what's the root reason why multiple
>>                 aggregations on streaming dataframe is not allowed
>>                 since it's a very useful feature, and flink has
>>                 supported it for a long time.
>>                 Thanks.

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