Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

That was fast!  Seems to be working. 
Thank you Fabian! 

> On 17 Nov 2016, at 13:58, Fabian Hueske  wrote:
> 
> Hi Paris,
> 
> just gave you the permissions (I hope).
> Let me know if something does not work.
> 
> Cheers, Fabian
> 
> 2016-11-17 13:48 GMT+01:00 Paris Carbone :
> 
>> We do not have to schedule this for an early Flink release, just saying.
>> I would just like to get the changes out and you people can review it and
>> integrate it anytime at your own pace.
>> 
>> Who is the admin of the wiki? It would be nice to get write access.
>> 
>>> On 17 Nov 2016, at 13:45, Paris Carbone  wrote:
>>> 
>>> Sounds like a plan!
>>> 
>>> Can someone grant me access to write in the wiki please?
>>> My username is “senorcarbone”.
>>> 
>>> Paris
>>> 
 On 16 Nov 2016, at 14:30, Gyula Fóra  wrote:
 
 I am not completely sure whether we should deprecate the old API for
>> 1.2 or
 remove it completely. Personally I am in favor of removing it, I don't
 think it is a huge burden to move to the new one if it makes for a much
 nicer user experience.
 
 I think you can go ahead add the FLIP to the wiki and open the PR so we
>> can
 start the review if you have it ready anyways.
 
 Gyula
 
 Paris Carbone  ezt írta (időpont: 2016. nov. 16., Sze,
 11:55):
 
> Thanks for reviewing, Gyula.
> 
> One thing that is still up to discussion is whether we should remove
> completely the old iterations API or simply mark it as deprecated till
>> v2.0.
> Also, not sure what is the best process now. We have the changes ready.
> Should I copy the FLIP to the wiki and trigger the PRs or wait for a
>> few
> more days in case someone has objections?
> 
> @Stephan, what is your take on our interpretation of the approach you
> suggested? Should we proceed or is there anything that you do not find
>> nice?
> 
> Paris
> 
>> On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
>> 
>> Hi Paris,
>> 
>> I like the proposed changes to the iteration API, this cleans up
>> things
> in
>> the Java API without any strict restriction I think (it was never a
> problem
>> in the Scala API).
>> 
>> The termination algorithm based on the proposed scoped loops seems to
>> be
>> fairly simple and looks good :)
>> 
>> Cheers,
>> Gyula
>> 
>> Paris Carbone  ezt írta (időpont: 2016. nov. 14., H,
> 8:50):
>> 
>>> That would be great Shi! Let's take that offline.
>>> 
>>> Anyone else interested in the iteration changes? It would be nice to
>>> incorporate these to v1.2 if possible so I count on your review asap.
>>> 
>>> cheers,
>>> Paris
>>> 
>>> On Nov 14, 2016, at 2:59 AM, xiaogang.sxg <
>> xiaogang@alibaba-inc.com
>>> > wrote:
>>> 
>>> Hi Paris
>>> 
>>> Unfortunately, the project is not public yet.
>>> But i can provide you a primitive implementation of the update
>> protocol
> in
>>> the paper. It’s implemented in Storm. Since the protocol assumes the
>>> communication channels between different tasks are dual, i think it’s
> not
>>> easy to adapt it to Flink.
>>> 
>>> Regards
>>> Xiaogang
>>> 
>>> 
>>> 在 2016年11月12日，上午3:03，Paris Carbone > kth.se
>>> 
>>> 写道：
>>> 
>>> Hi Shi,
>>> 
>>> Naiad/Timely Dataflow and other projects use global coordination
>> which
> is
>>> very convenient for asynchronous progress tracking in general but it
>> has
>>> some downsides in a production systems that count on in-flight
>>> transactional control mechanisms and rollback recovery guarantees.
>> This
> is
>>> why we generally prefer decentralized approaches (despite their our
>>> downsides).
>>> 
>>> Regarding synchronous/structured iterations, this is a bit off topic
>> and
>>> they are a bit of a different story as you already know.
>>> We maintain a graph streaming (gelly-streams) library on Flink that
>> you
>>> might find interesting [1]. Vasia, another Flink committer is also
> working
>>> on that among others.
>>> You can keep an eye on it since we are planning to use this project
>> as a
>>> showcase for a new way of doing structured and fixpoint iterations on
>>> streams in the future.
>>> 
>>> P.S. many thanks for sharing your publication, it was an interesting
> read.
>>> Do you happen to have your source code public? We could most
>> certainly
> use
>>> it in an benchmark soon.
>>> 
>>> [1] https://github.com/vasia/gelly-streaming
>>> 
>>> 
>>> On 11 Nov 2016, at 19:18, SHI Xiaogang > mailto:
>>> 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Fabian Hueske]

Hi Paris,

just gave you the permissions (I hope).
Let me know if something does not work.

Cheers, Fabian

2016-11-17 13:48 GMT+01:00 Paris Carbone :

> We do not have to schedule this for an early Flink release, just saying.
> I would just like to get the changes out and you people can review it and
> integrate it anytime at your own pace.
>
> Who is the admin of the wiki? It would be nice to get write access.
>
> > On 17 Nov 2016, at 13:45, Paris Carbone  wrote:
> >
> > Sounds like a plan!
> >
> > Can someone grant me access to write in the wiki please?
> > My username is “senorcarbone”.
> >
> > Paris
> >
> >> On 16 Nov 2016, at 14:30, Gyula Fóra  wrote:
> >>
> >> I am not completely sure whether we should deprecate the old API for
> 1.2 or
> >> remove it completely. Personally I am in favor of removing it, I don't
> >> think it is a huge burden to move to the new one if it makes for a much
> >> nicer user experience.
> >>
> >> I think you can go ahead add the FLIP to the wiki and open the PR so we
> can
> >> start the review if you have it ready anyways.
> >>
> >> Gyula
> >>
> >> Paris Carbone  ezt írta (időpont: 2016. nov. 16., Sze,
> >> 11:55):
> >>
> >>> Thanks for reviewing, Gyula.
> >>>
> >>> One thing that is still up to discussion is whether we should remove
> >>> completely the old iterations API or simply mark it as deprecated till
> v2.0.
> >>> Also, not sure what is the best process now. We have the changes ready.
> >>> Should I copy the FLIP to the wiki and trigger the PRs or wait for a
> few
> >>> more days in case someone has objections?
> >>>
> >>> @Stephan, what is your take on our interpretation of the approach you
> >>> suggested? Should we proceed or is there anything that you do not find
> nice?
> >>>
> >>> Paris
> >>>
>  On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
> 
>  Hi Paris,
> 
>  I like the proposed changes to the iteration API, this cleans up
> things
> >>> in
>  the Java API without any strict restriction I think (it was never a
> >>> problem
>  in the Scala API).
> 
>  The termination algorithm based on the proposed scoped loops seems to
> be
>  fairly simple and looks good :)
> 
>  Cheers,
>  Gyula
> 
>  Paris Carbone  ezt írta (időpont: 2016. nov. 14., H,
> >>> 8:50):
> 
> > That would be great Shi! Let's take that offline.
> >
> > Anyone else interested in the iteration changes? It would be nice to
> > incorporate these to v1.2 if possible so I count on your review asap.
> >
> > cheers,
> > Paris
> >
> > On Nov 14, 2016, at 2:59 AM, xiaogang.sxg <
> xiaogang@alibaba-inc.com
> > > wrote:
> >
> > Hi Paris
> >
> > Unfortunately, the project is not public yet.
> > But i can provide you a primitive implementation of the update
> protocol
> >>> in
> > the paper. It’s implemented in Storm. Since the protocol assumes the
> > communication channels between different tasks are dual, i think it’s
> >>> not
> > easy to adapt it to Flink.
> >
> > Regards
> > Xiaogang
> >
> >
> > 在 2016年11月12日，上午3:03，Paris Carbone  kth.se
> >
> > 写道：
> >
> > Hi Shi,
> >
> > Naiad/Timely Dataflow and other projects use global coordination
> which
> >>> is
> > very convenient for asynchronous progress tracking in general but it
> has
> > some downsides in a production systems that count on in-flight
> > transactional control mechanisms and rollback recovery guarantees.
> This
> >>> is
> > why we generally prefer decentralized approaches (despite their our
> > downsides).
> >
> > Regarding synchronous/structured iterations, this is a bit off topic
> and
> > they are a bit of a different story as you already know.
> > We maintain a graph streaming (gelly-streams) library on Flink that
> you
> > might find interesting [1]. Vasia, another Flink committer is also
> >>> working
> > on that among others.
> > You can keep an eye on it since we are planning to use this project
> as a
> > showcase for a new way of doing structured and fixpoint iterations on
> > streams in the future.
> >
> > P.S. many thanks for sharing your publication, it was an interesting
> >>> read.
> > Do you happen to have your source code public? We could most
> certainly
> >>> use
> > it in an benchmark soon.
> >
> > [1] https://github.com/vasia/gelly-streaming
> >
> >
> > On 11 Nov 2016, at 19:18, SHI Xiaogang  mailto:
> > shixiaoga...@gmail.com>> wrote:
> >
> > Hi, Fouad
> >
> > Thank you for the explanation. Now the centralized method seems
> correct
> >>> to
> > me.
> > The passing of StatusUpdate events 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

We do not have to schedule this for an early Flink release, just saying.
I would just like to get the changes out and you people can review it and 
integrate it anytime at your own pace.

Who is the admin of the wiki? It would be nice to get write access.

> On 17 Nov 2016, at 13:45, Paris Carbone  wrote:
> 
> Sounds like a plan!
> 
> Can someone grant me access to write in the wiki please?
> My username is “senorcarbone”.
> 
> Paris
> 
>> On 16 Nov 2016, at 14:30, Gyula Fóra  wrote:
>> 
>> I am not completely sure whether we should deprecate the old API for 1.2 or
>> remove it completely. Personally I am in favor of removing it, I don't
>> think it is a huge burden to move to the new one if it makes for a much
>> nicer user experience.
>> 
>> I think you can go ahead add the FLIP to the wiki and open the PR so we can
>> start the review if you have it ready anyways.
>> 
>> Gyula
>> 
>> Paris Carbone  ezt írta (időpont: 2016. nov. 16., Sze,
>> 11:55):
>> 
>>> Thanks for reviewing, Gyula.
>>> 
>>> One thing that is still up to discussion is whether we should remove
>>> completely the old iterations API or simply mark it as deprecated till v2.0.
>>> Also, not sure what is the best process now. We have the changes ready.
>>> Should I copy the FLIP to the wiki and trigger the PRs or wait for a few
>>> more days in case someone has objections?
>>> 
>>> @Stephan, what is your take on our interpretation of the approach you
>>> suggested? Should we proceed or is there anything that you do not find nice?
>>> 
>>> Paris
>>> 
 On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
 
 Hi Paris,
 
 I like the proposed changes to the iteration API, this cleans up things
>>> in
 the Java API without any strict restriction I think (it was never a
>>> problem
 in the Scala API).
 
 The termination algorithm based on the proposed scoped loops seems to be
 fairly simple and looks good :)
 
 Cheers,
 Gyula
 
 Paris Carbone  ezt írta (időpont: 2016. nov. 14., H,
>>> 8:50):
 
> That would be great Shi! Let's take that offline.
> 
> Anyone else interested in the iteration changes? It would be nice to
> incorporate these to v1.2 if possible so I count on your review asap.
> 
> cheers,
> Paris
> 
> On Nov 14, 2016, at 2:59 AM, xiaogang.sxg  > wrote:
> 
> Hi Paris
> 
> Unfortunately, the project is not public yet.
> But i can provide you a primitive implementation of the update protocol
>>> in
> the paper. It’s implemented in Storm. Since the protocol assumes the
> communication channels between different tasks are dual, i think it’s
>>> not
> easy to adapt it to Flink.
> 
> Regards
> Xiaogang
> 
> 
> 在 2016年11月12日，上午3:03，Paris Carbone  
> 写道：
> 
> Hi Shi,
> 
> Naiad/Timely Dataflow and other projects use global coordination which
>>> is
> very convenient for asynchronous progress tracking in general but it has
> some downsides in a production systems that count on in-flight
> transactional control mechanisms and rollback recovery guarantees. This
>>> is
> why we generally prefer decentralized approaches (despite their our
> downsides).
> 
> Regarding synchronous/structured iterations, this is a bit off topic and
> they are a bit of a different story as you already know.
> We maintain a graph streaming (gelly-streams) library on Flink that you
> might find interesting [1]. Vasia, another Flink committer is also
>>> working
> on that among others.
> You can keep an eye on it since we are planning to use this project as a
> showcase for a new way of doing structured and fixpoint iterations on
> streams in the future.
> 
> P.S. many thanks for sharing your publication, it was an interesting
>>> read.
> Do you happen to have your source code public? We could most certainly
>>> use
> it in an benchmark soon.
> 
> [1] https://github.com/vasia/gelly-streaming
> 
> 
> On 11 Nov 2016, at 19:18, SHI Xiaogang > wrote:
> 
> Hi, Fouad
> 
> Thank you for the explanation. Now the centralized method seems correct
>>> to
> me.
> The passing of StatusUpdate events will lead to synchronous iterations
>>> and
> we are using the information in each iterations to terminate the
> computation.
> 
> Actually, i prefer the centralized method because in many applications,
>>> the
> convergence may depend on some global statistics.
> For example, a PageRank program may terminate the computation when 99%
> vertices are converged.
> I think those learning programs which cannot 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

Sounds like a plan!

Can someone grant me access to write in the wiki please?
My username is “senorcarbone”.

Paris

> On 16 Nov 2016, at 14:30, Gyula Fóra  wrote:
> 
> I am not completely sure whether we should deprecate the old API for 1.2 or
> remove it completely. Personally I am in favor of removing it, I don't
> think it is a huge burden to move to the new one if it makes for a much
> nicer user experience.
> 
> I think you can go ahead add the FLIP to the wiki and open the PR so we can
> start the review if you have it ready anyways.
> 
> Gyula
> 
> Paris Carbone  ezt írta (időpont: 2016. nov. 16., Sze,
> 11:55):
> 
>> Thanks for reviewing, Gyula.
>> 
>> One thing that is still up to discussion is whether we should remove
>> completely the old iterations API or simply mark it as deprecated till v2.0.
>> Also, not sure what is the best process now. We have the changes ready.
>> Should I copy the FLIP to the wiki and trigger the PRs or wait for a few
>> more days in case someone has objections?
>> 
>> @Stephan, what is your take on our interpretation of the approach you
>> suggested? Should we proceed or is there anything that you do not find nice?
>> 
>> Paris
>> 
>>> On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
>>> 
>>> Hi Paris,
>>> 
>>> I like the proposed changes to the iteration API, this cleans up things
>> in
>>> the Java API without any strict restriction I think (it was never a
>> problem
>>> in the Scala API).
>>> 
>>> The termination algorithm based on the proposed scoped loops seems to be
>>> fairly simple and looks good :)
>>> 
>>> Cheers,
>>> Gyula
>>> 
>>> Paris Carbone  ezt írta (időpont: 2016. nov. 14., H,
>> 8:50):
>>> 
 That would be great Shi! Let's take that offline.
 
 Anyone else interested in the iteration changes? It would be nice to
 incorporate these to v1.2 if possible so I count on your review asap.
 
 cheers,
 Paris
 
 On Nov 14, 2016, at 2:59 AM, xiaogang.sxg > wrote:
 
 Hi Paris
 
 Unfortunately, the project is not public yet.
 But i can provide you a primitive implementation of the update protocol
>> in
 the paper. It’s implemented in Storm. Since the protocol assumes the
 communication channels between different tasks are dual, i think it’s
>> not
 easy to adapt it to Flink.
 
 Regards
 Xiaogang
 
 
 在 2016年11月12日，上午3:03，Paris Carbone > is
 very convenient for asynchronous progress tracking in general but it has
 some downsides in a production systems that count on in-flight
 transactional control mechanisms and rollback recovery guarantees. This
>> is
 why we generally prefer decentralized approaches (despite their our
 downsides).
 
 Regarding synchronous/structured iterations, this is a bit off topic and
 they are a bit of a different story as you already know.
 We maintain a graph streaming (gelly-streams) library on Flink that you
 might find interesting [1]. Vasia, another Flink committer is also
>> working
 on that among others.
 You can keep an eye on it since we are planning to use this project as a
 showcase for a new way of doing structured and fixpoint iterations on
 streams in the future.
 
 P.S. many thanks for sharing your publication, it was an interesting
>> read.
 Do you happen to have your source code public? We could most certainly
>> use
 it in an benchmark soon.
 
 [1] https://github.com/vasia/gelly-streaming
 
 
 On 11 Nov 2016, at 19:18, SHI Xiaogang >> shixiaoga...@gmail.com>> wrote:
 
 Hi, Fouad
 
 Thank you for the explanation. Now the centralized method seems correct
>> to
 me.
 The passing of StatusUpdate events will lead to synchronous iterations
>> and
 we are using the information in each iterations to terminate the
 computation.
 
 Actually, i prefer the centralized method because in many applications,
>> the
 convergence may depend on some global statistics.
 For example, a PageRank program may terminate the computation when 99%
 vertices are converged.
 I think those learning programs which cannot reach the fixed-point
 (oscillating around the fixed-point) can benefit a lot from such
>> features.
 The decentralized method makes it hard to support such convergence
 conditions.
 
 
 Another concern is that Flink cannot produce periodical results in the
 iteration over infinite data streams.
 Take a concrete example. Given an edge stream constructing a graph, the
 user may need the PageRank weight of each vertex in the 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Gyula Fóra]

I am not completely sure whether we should deprecate the old API for 1.2 or
remove it completely. Personally I am in favor of removing it, I don't
think it is a huge burden to move to the new one if it makes for a much
nicer user experience.

I think you can go ahead add the FLIP to the wiki and open the PR so we can
start the review if you have it ready anyways.

Gyula

Paris Carbone  ezt írta (időpont: 2016. nov. 16., Sze,
11:55):

> Thanks for reviewing, Gyula.
>
> One thing that is still up to discussion is whether we should remove
> completely the old iterations API or simply mark it as deprecated till v2.0.
> Also, not sure what is the best process now. We have the changes ready.
> Should I copy the FLIP to the wiki and trigger the PRs or wait for a few
> more days in case someone has objections?
>
> @Stephan, what is your take on our interpretation of the approach you
> suggested? Should we proceed or is there anything that you do not find nice?
>
> Paris
>
> > On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
> >
> > Hi Paris,
> >
> > I like the proposed changes to the iteration API, this cleans up things
> in
> > the Java API without any strict restriction I think (it was never a
> problem
> > in the Scala API).
> >
> > The termination algorithm based on the proposed scoped loops seems to be
> > fairly simple and looks good :)
> >
> > Cheers,
> > Gyula
> >
> > Paris Carbone  ezt írta (időpont: 2016. nov. 14., H,
> 8:50):
> >
> >> That would be great Shi! Let's take that offline.
> >>
> >> Anyone else interested in the iteration changes? It would be nice to
> >> incorporate these to v1.2 if possible so I count on your review asap.
> >>
> >> cheers,
> >> Paris
> >>
> >> On Nov 14, 2016, at 2:59 AM, xiaogang.sxg  >> > wrote:
> >>
> >> Hi Paris
> >>
> >> Unfortunately, the project is not public yet.
> >> But i can provide you a primitive implementation of the update protocol
> in
> >> the paper. It’s implemented in Storm. Since the protocol assumes the
> >> communication channels between different tasks are dual, i think it’s
> not
> >> easy to adapt it to Flink.
> >>
> >> Regards
> >> Xiaogang
> >>
> >>
> >> 在 2016年11月12日，上午3:03，Paris Carbone  >>
> >> 写道：
> >>
> >> Hi Shi,
> >>
> >> Naiad/Timely Dataflow and other projects use global coordination which
> is
> >> very convenient for asynchronous progress tracking in general but it has
> >> some downsides in a production systems that count on in-flight
> >> transactional control mechanisms and rollback recovery guarantees. This
> is
> >> why we generally prefer decentralized approaches (despite their our
> >> downsides).
> >>
> >> Regarding synchronous/structured iterations, this is a bit off topic and
> >> they are a bit of a different story as you already know.
> >> We maintain a graph streaming (gelly-streams) library on Flink that you
> >> might find interesting [1]. Vasia, another Flink committer is also
> working
> >> on that among others.
> >> You can keep an eye on it since we are planning to use this project as a
> >> showcase for a new way of doing structured and fixpoint iterations on
> >> streams in the future.
> >>
> >> P.S. many thanks for sharing your publication, it was an interesting
> read.
> >> Do you happen to have your source code public? We could most certainly
> use
> >> it in an benchmark soon.
> >>
> >> [1] https://github.com/vasia/gelly-streaming
> >>
> >>
> >> On 11 Nov 2016, at 19:18, SHI Xiaogang > shixiaoga...@gmail.com>> wrote:
> >>
> >> Hi, Fouad
> >>
> >> Thank you for the explanation. Now the centralized method seems correct
> to
> >> me.
> >> The passing of StatusUpdate events will lead to synchronous iterations
> and
> >> we are using the information in each iterations to terminate the
> >> computation.
> >>
> >> Actually, i prefer the centralized method because in many applications,
> the
> >> convergence may depend on some global statistics.
> >> For example, a PageRank program may terminate the computation when 99%
> >> vertices are converged.
> >> I think those learning programs which cannot reach the fixed-point
> >> (oscillating around the fixed-point) can benefit a lot from such
> features.
> >> The decentralized method makes it hard to support such convergence
> >> conditions.
> >>
> >>
> >> Another concern is that Flink cannot produce periodical results in the
> >> iteration over infinite data streams.
> >> Take a concrete example. Given an edge stream constructing a graph, the
> >> user may need the PageRank weight of each vertex in the graphs formed at
> >> certain instants.
> >> Currently Flink does not provide any input or iteration information to
> >> users, making users hard to implement such real-time iterative
> >> applications.
> >> Such features are supported in both Naiad and Tornado. I think 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

Thanks for reviewing, Gyula.

One thing that is still up to discussion is whether we should remove completely 
the old iterations API or simply mark it as deprecated till v2.0.
Also, not sure what is the best process now. We have the changes ready. Should 
I copy the FLIP to the wiki and trigger the PRs or wait for a few more days in 
case someone has objections?

@Stephan, what is your take on our interpretation of the approach you 
suggested? Should we proceed or is there anything that you do not find nice?

Paris

> On 15 Nov 2016, at 10:01, Gyula Fóra  wrote:
> 
> Hi Paris,
> 
> I like the proposed changes to the iteration API, this cleans up things in
> the Java API without any strict restriction I think (it was never a problem
> in the Scala API).
> 
> The termination algorithm based on the proposed scoped loops seems to be
> fairly simple and looks good :)
> 
> Cheers,
> Gyula
> 
> Paris Carbone  ezt írta (időpont: 2016. nov. 14., H, 8:50):
> 
>> That would be great Shi! Let's take that offline.
>> 
>> Anyone else interested in the iteration changes? It would be nice to
>> incorporate these to v1.2 if possible so I count on your review asap.
>> 
>> cheers,
>> Paris
>> 
>> On Nov 14, 2016, at 2:59 AM, xiaogang.sxg > > wrote:
>> 
>> Hi Paris
>> 
>> Unfortunately, the project is not public yet.
>> But i can provide you a primitive implementation of the update protocol in
>> the paper. It’s implemented in Storm. Since the protocol assumes the
>> communication channels between different tasks are dual, i think it’s not
>> easy to adapt it to Flink.
>> 
>> Regards
>> Xiaogang
>> 
>> 
>> 在 2016年11月12日，上午3:03，Paris Carbone >
>> 写道：
>> 
>> Hi Shi,
>> 
>> Naiad/Timely Dataflow and other projects use global coordination which is
>> very convenient for asynchronous progress tracking in general but it has
>> some downsides in a production systems that count on in-flight
>> transactional control mechanisms and rollback recovery guarantees. This is
>> why we generally prefer decentralized approaches (despite their our
>> downsides).
>> 
>> Regarding synchronous/structured iterations, this is a bit off topic and
>> they are a bit of a different story as you already know.
>> We maintain a graph streaming (gelly-streams) library on Flink that you
>> might find interesting [1]. Vasia, another Flink committer is also working
>> on that among others.
>> You can keep an eye on it since we are planning to use this project as a
>> showcase for a new way of doing structured and fixpoint iterations on
>> streams in the future.
>> 
>> P.S. many thanks for sharing your publication, it was an interesting read.
>> Do you happen to have your source code public? We could most certainly use
>> it in an benchmark soon.
>> 
>> [1] https://github.com/vasia/gelly-streaming
>> 
>> 
>> On 11 Nov 2016, at 19:18, SHI Xiaogang  shixiaoga...@gmail.com>> wrote:
>> 
>> Hi, Fouad
>> 
>> Thank you for the explanation. Now the centralized method seems correct to
>> me.
>> The passing of StatusUpdate events will lead to synchronous iterations and
>> we are using the information in each iterations to terminate the
>> computation.
>> 
>> Actually, i prefer the centralized method because in many applications, the
>> convergence may depend on some global statistics.
>> For example, a PageRank program may terminate the computation when 99%
>> vertices are converged.
>> I think those learning programs which cannot reach the fixed-point
>> (oscillating around the fixed-point) can benefit a lot from such features.
>> The decentralized method makes it hard to support such convergence
>> conditions.
>> 
>> 
>> Another concern is that Flink cannot produce periodical results in the
>> iteration over infinite data streams.
>> Take a concrete example. Given an edge stream constructing a graph, the
>> user may need the PageRank weight of each vertex in the graphs formed at
>> certain instants.
>> Currently Flink does not provide any input or iteration information to
>> users, making users hard to implement such real-time iterative
>> applications.
>> Such features are supported in both Naiad and Tornado. I think Flink should
>> support it as well.
>> 
>> What do you think?
>> 
>> Regards
>> Xiaogang
>> 
>> 
>> 2016-11-11 19:27 GMT+08:00 Fouad ALi  fouad.alsay...@gmail.com>>:
>> 
>> Hi Shi,
>> 
>> It seems that you are referring to the centralized algorithm which is no
>> longer the proposed version.
>> In the decentralized version (check last doc) there is no master node or
>> global coordination involved.
>> 
>> Let us keep this discussion to the decentralized one if possible.
>> 
>> To answer your points on the previous approach, there is a catch in your
>> trace at t7. Here is what is happening :
>> - Head,as 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Gyula Fóra]

Hi Paris,

I like the proposed changes to the iteration API, this cleans up things in
the Java API without any strict restriction I think (it was never a problem
in the Scala API).

The termination algorithm based on the proposed scoped loops seems to be
fairly simple and looks good :)

Cheers,
Gyula

Paris Carbone  ezt írta (időpont: 2016. nov. 14., H, 8:50):

> That would be great Shi! Let's take that offline.
>
> Anyone else interested in the iteration changes? It would be nice to
> incorporate these to v1.2 if possible so I count on your review asap.
>
> cheers,
> Paris
>
> On Nov 14, 2016, at 2:59 AM, xiaogang.sxg  > wrote:
>
> Hi Paris
>
> Unfortunately, the project is not public yet.
> But i can provide you a primitive implementation of the update protocol in
> the paper. It’s implemented in Storm. Since the protocol assumes the
> communication channels between different tasks are dual, i think it’s not
> easy to adapt it to Flink.
>
> Regards
> Xiaogang
>
>
> 在 2016年11月12日，上午3:03，Paris Carbone >
> 写道：
>
> Hi Shi,
>
> Naiad/Timely Dataflow and other projects use global coordination which is
> very convenient for asynchronous progress tracking in general but it has
> some downsides in a production systems that count on in-flight
> transactional control mechanisms and rollback recovery guarantees. This is
> why we generally prefer decentralized approaches (despite their our
> downsides).
>
> Regarding synchronous/structured iterations, this is a bit off topic and
> they are a bit of a different story as you already know.
> We maintain a graph streaming (gelly-streams) library on Flink that you
> might find interesting [1]. Vasia, another Flink committer is also working
> on that among others.
> You can keep an eye on it since we are planning to use this project as a
> showcase for a new way of doing structured and fixpoint iterations on
> streams in the future.
>
> P.S. many thanks for sharing your publication, it was an interesting read.
> Do you happen to have your source code public? We could most certainly use
> it in an benchmark soon.
>
> [1] https://github.com/vasia/gelly-streaming
>
>
> On 11 Nov 2016, at 19:18, SHI Xiaogang > wrote:
>
> Hi, Fouad
>
> Thank you for the explanation. Now the centralized method seems correct to
> me.
> The passing of StatusUpdate events will lead to synchronous iterations and
> we are using the information in each iterations to terminate the
> computation.
>
> Actually, i prefer the centralized method because in many applications, the
> convergence may depend on some global statistics.
> For example, a PageRank program may terminate the computation when 99%
> vertices are converged.
> I think those learning programs which cannot reach the fixed-point
> (oscillating around the fixed-point) can benefit a lot from such features.
> The decentralized method makes it hard to support such convergence
> conditions.
>
>
> Another concern is that Flink cannot produce periodical results in the
> iteration over infinite data streams.
> Take a concrete example. Given an edge stream constructing a graph, the
> user may need the PageRank weight of each vertex in the graphs formed at
> certain instants.
> Currently Flink does not provide any input or iteration information to
> users, making users hard to implement such real-time iterative
> applications.
> Such features are supported in both Naiad and Tornado. I think Flink should
> support it as well.
>
> What do you think?
>
> Regards
> Xiaogang
>
>
> 2016-11-11 19:27 GMT+08:00 Fouad ALi >:
>
> Hi Shi,
>
> It seems that you are referring to the centralized algorithm which is no
> longer the proposed version.
> In the decentralized version (check last doc) there is no master node or
> global coordination involved.
>
> Let us keep this discussion to the decentralized one if possible.
>
> To answer your points on the previous approach, there is a catch in your
> trace at t7. Here is what is happening :
> - Head,as well as RS, will receive  a 'BroadcastStatusUpdate' from
> runtime (see 2.1 in the steps).
> - RS and Heads will broadcast StatusUpdate  event and will not notify its
> status.
> - When StatusUpdate event gets back to the head it will notify its
> WORKING  status.
>
> Hope that answers your concern.
>
> Best,
> Fouad
>
> On Nov 11, 2016, at 6:21 AM, SHI Xiaogang >
> wrote:
>
> Hi Paris
>
> I have several concerns about the correctness of the termination
> protocol.
> I think the termination protocol put an end to the computation even when
> the computation has not converged.
>
> Suppose there exists a loop context constructed by a OP operator, a Head
> operator and a 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

That would be great Shi! Let's take that offline.

Anyone else interested in the iteration changes? It would be nice to 
incorporate these to v1.2 if possible so I count on your review asap.

cheers,
Paris

On Nov 14, 2016, at 2:59 AM, xiaogang.sxg 
> wrote:

Hi Paris

Unfortunately, the project is not public yet.
But i can provide you a primitive implementation of the update protocol in the 
paper. It’s implemented in Storm. Since the protocol assumes the communication 
channels between different tasks are dual, i think it’s not easy to adapt it to 
Flink.

Regards
Xiaogang


在 2016年11月12日，上午3:03，Paris Carbone > 写道：

Hi Shi,

Naiad/Timely Dataflow and other projects use global coordination which is very 
convenient for asynchronous progress tracking in general but it has some 
downsides in a production systems that count on in-flight transactional control 
mechanisms and rollback recovery guarantees. This is why we generally prefer 
decentralized approaches (despite their our downsides).

Regarding synchronous/structured iterations, this is a bit off topic and they 
are a bit of a different story as you already know.
We maintain a graph streaming (gelly-streams) library on Flink that you might 
find interesting [1]. Vasia, another Flink committer is also working on that 
among others.
You can keep an eye on it since we are planning to use this project as a 
showcase for a new way of doing structured and fixpoint iterations on streams 
in the future.

P.S. many thanks for sharing your publication, it was an interesting read. Do 
you happen to have your source code public? We could most certainly use it in 
an benchmark soon.

[1] https://github.com/vasia/gelly-streaming


On 11 Nov 2016, at 19:18, SHI Xiaogang 
>
 wrote:

Hi, Fouad

Thank you for the explanation. Now the centralized method seems correct to
me.
The passing of StatusUpdate events will lead to synchronous iterations and
we are using the information in each iterations to terminate the
computation.

Actually, i prefer the centralized method because in many applications, the
convergence may depend on some global statistics.
For example, a PageRank program may terminate the computation when 99%
vertices are converged.
I think those learning programs which cannot reach the fixed-point
(oscillating around the fixed-point) can benefit a lot from such features.
The decentralized method makes it hard to support such convergence
conditions.


Another concern is that Flink cannot produce periodical results in the
iteration over infinite data streams.
Take a concrete example. Given an edge stream constructing a graph, the
user may need the PageRank weight of each vertex in the graphs formed at
certain instants.
Currently Flink does not provide any input or iteration information to
users, making users hard to implement such real-time iterative applications.
Such features are supported in both Naiad and Tornado. I think Flink should
support it as well.

What do you think?

Regards
Xiaogang


2016-11-11 19:27 GMT+08:00 Fouad ALi 
>:

Hi Shi,

It seems that you are referring to the centralized algorithm which is no
longer the proposed version.
In the decentralized version (check last doc) there is no master node or
global coordination involved.

Let us keep this discussion to the decentralized one if possible.

To answer your points on the previous approach, there is a catch in your
trace at t7. Here is what is happening :
- Head,as well as RS, will receive  a 'BroadcastStatusUpdate' from
runtime (see 2.1 in the steps).
- RS and Heads will broadcast StatusUpdate  event and will not notify its
status.
- When StatusUpdate event gets back to the head it will notify its
WORKING  status.

Hope that answers your concern.

Best,
Fouad

On Nov 11, 2016, at 6:21 AM, SHI Xiaogang 
>
wrote:

Hi Paris

I have several concerns about the correctness of the termination
protocol.
I think the termination protocol put an end to the computation even when
the computation has not converged.

Suppose there exists a loop context constructed by a OP operator, a Head
operator and a Tail operator (illustrated in Figure 2 in the first
draft).
The stream only contains one record. OP will pass the record to its
downstream operators 10 times. In other words, the loop should iterate 10
times.

If I understood the protocol correctly, the following event sequence may
happen in the computation:
t1:  RS emits Record to OP. Since RS has reached the "end-of-stream", the
system enters into Speculative Phase.
t2:  OP receives Record and emits it to TAIL.
t3:  HEAD receives the UpdateStatus event, and notifies with an IDLE
state.
t4. OP 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Paris Carbone]

Hi Shi,

Naiad/Timely Dataflow and other projects use global coordination which is very 
convenient for asynchronous progress tracking in general but it has some 
downsides in a production systems that count on in-flight transactional control 
mechanisms and rollback recovery guarantees. This is why we generally prefer 
decentralized approaches (despite their our downsides).

Regarding synchronous/structured iterations, this is a bit off topic and they 
are a bit of a different story as you already know.
We maintain a graph streaming (gelly-streams) library on Flink that you might 
find interesting [1]. Vasia, another Flink committer is also working on that 
among others.
You can keep an eye on it since we are planning to use this project as a 
showcase for a new way of doing structured and fixpoint iterations on streams 
in the future.

P.S. many thanks for sharing your publication, it was an interesting read. Do 
you happen to have your source code public? We could most certainly use it in 
an benchmark soon.

[1] https://github.com/vasia/gelly-streaming


On 11 Nov 2016, at 19:18, SHI Xiaogang 
> wrote:

Hi, Fouad

Thank you for the explanation. Now the centralized method seems correct to
me.
The passing of StatusUpdate events will lead to synchronous iterations and
we are using the information in each iterations to terminate the
computation.

Actually, i prefer the centralized method because in many applications, the
convergence may depend on some global statistics.
For example, a PageRank program may terminate the computation when 99%
vertices are converged.
I think those learning programs which cannot reach the fixed-point
(oscillating around the fixed-point) can benefit a lot from such features.
The decentralized method makes it hard to support such convergence
conditions.


Another concern is that Flink cannot produce periodical results in the
iteration over infinite data streams.
Take a concrete example. Given an edge stream constructing a graph, the
user may need the PageRank weight of each vertex in the graphs formed at
certain instants.
Currently Flink does not provide any input or iteration information to
users, making users hard to implement such real-time iterative applications.
Such features are supported in both Naiad and Tornado. I think Flink should
support it as well.

What do you think?

Regards
Xiaogang


2016-11-11 19:27 GMT+08:00 Fouad ALi 
>:

Hi Shi,

It seems that you are referring to the centralized algorithm which is no
longer the proposed version.
In the decentralized version (check last doc) there is no master node or
global coordination involved.

Let us keep this discussion to the decentralized one if possible.

To answer your points on the previous approach, there is a catch in your
trace at t7. Here is what is happening :
- Head,as well as RS, will receive  a 'BroadcastStatusUpdate' from
runtime (see 2.1 in the steps).
- RS and Heads will broadcast StatusUpdate  event and will not notify its
status.
- When StatusUpdate event gets back to the head it will notify its
WORKING  status.

Hope that answers your concern.

Best,
Fouad

On Nov 11, 2016, at 6:21 AM, SHI Xiaogang 
>
wrote:

Hi Paris

I have several concerns about the correctness of the termination
protocol.
I think the termination protocol put an end to the computation even when
the computation has not converged.

Suppose there exists a loop context constructed by a OP operator, a Head
operator and a Tail operator (illustrated in Figure 2 in the first
draft).
The stream only contains one record. OP will pass the record to its
downstream operators 10 times. In other words, the loop should iterate 10
times.

If I understood the protocol correctly, the following event sequence may
happen in the computation:
t1:  RS emits Record to OP. Since RS has reached the "end-of-stream", the
system enters into Speculative Phase.
t2:  OP receives Record and emits it to TAIL.
t3:  HEAD receives the UpdateStatus event, and notifies with an IDLE
state.
t4. OP receives the UpdateStatus event from HEAD, and notifies with an
WORKING state.
t5. TAIL receives Record and emits it to HEAD.
t6. TAIL receives the UpdateStatus event from OP, and notifies with an
WORKING state.
t7. The system starts a new attempt. HEAD receives the UpdateStatus event
and notifies with an IDLE state.  (Record is still in transition.)
t8. OP receives the UpdateStatus event from HEAD and notifies with an
IDLE
state.
t9. TAIL receives the UpdateStatus event from OP and notifies with an
IDLE
state.
t10. HEAD receives Record from TAIL and emits it to OP.
t11. System puts an end to the computation.

Though the computation is expected to iterate 10 times, it ends earlier.
The cause is that the communication channels of MASTER=>HEAD and
TAIL=>HEAD
are not synchronized.

I think the protocol follows the idea 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[SHI Xiaogang]

Hi, Fouad

Thank you for the explanation. Now the centralized method seems correct to
me.
The passing of StatusUpdate events will lead to synchronous iterations and
we are using the information in each iterations to terminate the
computation.

Actually, i prefer the centralized method because in many applications, the
convergence may depend on some global statistics.
For example, a PageRank program may terminate the computation when 99%
vertices are converged.
I think those learning programs which cannot reach the fixed-point
(oscillating around the fixed-point) can benefit a lot from such features.
The decentralized method makes it hard to support such convergence
conditions.


Another concern is that Flink cannot produce periodical results in the
iteration over infinite data streams.
Take a concrete example. Given an edge stream constructing a graph, the
user may need the PageRank weight of each vertex in the graphs formed at
certain instants.
Currently Flink does not provide any input or iteration information to
users, making users hard to implement such real-time iterative applications.
Such features are supported in both Naiad and Tornado. I think Flink should
support it as well.

What do you think?

Regards
Xiaogang


2016-11-11 19:27 GMT+08:00 Fouad ALi :

> Hi Shi,
>
> It seems that you are referring to the centralized algorithm which is no
> longer the proposed version.
> In the decentralized version (check last doc) there is no master node or
> global coordination involved.
>
> Let us keep this discussion to the decentralized one if possible.
>
> To answer your points on the previous approach, there is a catch in your
> trace at t7. Here is what is happening :
>  - Head,as well as RS, will receive  a 'BroadcastStatusUpdate' from
> runtime (see 2.1 in the steps).
>  - RS and Heads will broadcast StatusUpdate  event and will not notify its
> status.
>  - When StatusUpdate event gets back to the head it will notify its
> WORKING  status.
>
> Hope that answers your concern.
>
> Best,
> Fouad
>
> > On Nov 11, 2016, at 6:21 AM, SHI Xiaogang 
> wrote:
> >
> > Hi Paris
> >
> > I have several concerns about the correctness of the termination
> protocol.
> > I think the termination protocol put an end to the computation even when
> > the computation has not converged.
> >
> > Suppose there exists a loop context constructed by a OP operator, a Head
> > operator and a Tail operator (illustrated in Figure 2 in the first
> draft).
> > The stream only contains one record. OP will pass the record to its
> > downstream operators 10 times. In other words, the loop should iterate 10
> > times.
> >
> > If I understood the protocol correctly, the following event sequence may
> > happen in the computation:
> > t1:  RS emits Record to OP. Since RS has reached the "end-of-stream", the
> > system enters into Speculative Phase.
> > t2:  OP receives Record and emits it to TAIL.
> > t3:  HEAD receives the UpdateStatus event, and notifies with an IDLE
> state.
> > t4. OP receives the UpdateStatus event from HEAD, and notifies with an
> > WORKING state.
> > t5. TAIL receives Record and emits it to HEAD.
> > t6. TAIL receives the UpdateStatus event from OP, and notifies with an
> > WORKING state.
> > t7. The system starts a new attempt. HEAD receives the UpdateStatus event
> > and notifies with an IDLE state.  (Record is still in transition.)
> > t8. OP receives the UpdateStatus event from HEAD and notifies with an
> IDLE
> > state.
> > t9. TAIL receives the UpdateStatus event from OP and notifies with an
> IDLE
> > state.
> > t10. HEAD receives Record from TAIL and emits it to OP.
> > t11. System puts an end to the computation.
> >
> > Though the computation is expected to iterate 10 times, it ends earlier.
> > The cause is that the communication channels of MASTER=>HEAD and
> TAIL=>HEAD
> > are not synchronized.
> >
> > I think the protocol follows the idea of the Chandy-Lamport algorithm to
> > determine a global state.
> > But the information of whether a node has processed any record to since
> the
> > last request is not STABLE.
> > Hence i doubt the correctness of the protocol.
> >
> > To determine the termination correctly, we need some information that is
> > stable.
> > In timelyflow, Naiad collects the progress made in each iteration and
> > terminates the loop when a little progress is made in an iteration
> > (identified by the timestamp vector).
> > The information is stable because the result of an iteration cannot be
> > changed by the execution of later iterations.
> >
> > A similar method is also adopted in Tornado.
> > You may see my paper for more details about the termination of loops:
> > http://net.pku.edu.cn/~cuibin/Papers/2016SIGMOD.pdf <
> http://net.pku.edu.cn/~cuibin/Papers/2016SIGMOD.pdf>
> >
> > Regards
> > Xiaogang
> >
> > 2016-11-11 3:19 GMT+08:00 Paris Carbone >:
> >
> >> Hi again Flink folks,
> >>
> >> Here is our 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[Fouad ALi]

Hi Shi,

It seems that you are referring to the centralized algorithm which is no longer 
the proposed version.
In the decentralized version (check last doc) there is no master node or global 
coordination involved.

Let us keep this discussion to the decentralized one if possible.

To answer your points on the previous approach, there is a catch in your trace 
at t7. Here is what is happening :
 - Head,as well as RS, will receive  a 'BroadcastStatusUpdate' from runtime 
(see 2.1 in the steps). 
 - RS and Heads will broadcast StatusUpdate  event and will not notify its 
status. 
 - When StatusUpdate event gets back to the head it will notify its WORKING  
status.

Hope that answers your concern.

Best,
Fouad

> On Nov 11, 2016, at 6:21 AM, SHI Xiaogang  wrote:
> 
> Hi Paris
> 
> I have several concerns about the correctness of the termination protocol.
> I think the termination protocol put an end to the computation even when
> the computation has not converged.
> 
> Suppose there exists a loop context constructed by a OP operator, a Head
> operator and a Tail operator (illustrated in Figure 2 in the first draft).
> The stream only contains one record. OP will pass the record to its
> downstream operators 10 times. In other words, the loop should iterate 10
> times.
> 
> If I understood the protocol correctly, the following event sequence may
> happen in the computation:
> t1:  RS emits Record to OP. Since RS has reached the "end-of-stream", the
> system enters into Speculative Phase.
> t2:  OP receives Record and emits it to TAIL.
> t3:  HEAD receives the UpdateStatus event, and notifies with an IDLE state.
> t4. OP receives the UpdateStatus event from HEAD, and notifies with an
> WORKING state.
> t5. TAIL receives Record and emits it to HEAD.
> t6. TAIL receives the UpdateStatus event from OP, and notifies with an
> WORKING state.
> t7. The system starts a new attempt. HEAD receives the UpdateStatus event
> and notifies with an IDLE state.  (Record is still in transition.)
> t8. OP receives the UpdateStatus event from HEAD and notifies with an IDLE
> state.
> t9. TAIL receives the UpdateStatus event from OP and notifies with an IDLE
> state.
> t10. HEAD receives Record from TAIL and emits it to OP.
> t11. System puts an end to the computation.
> 
> Though the computation is expected to iterate 10 times, it ends earlier.
> The cause is that the communication channels of MASTER=>HEAD and TAIL=>HEAD
> are not synchronized.
> 
> I think the protocol follows the idea of the Chandy-Lamport algorithm to
> determine a global state.
> But the information of whether a node has processed any record to since the
> last request is not STABLE.
> Hence i doubt the correctness of the protocol.
> 
> To determine the termination correctly, we need some information that is
> stable.
> In timelyflow, Naiad collects the progress made in each iteration and
> terminates the loop when a little progress is made in an iteration
> (identified by the timestamp vector).
> The information is stable because the result of an iteration cannot be
> changed by the execution of later iterations.
> 
> A similar method is also adopted in Tornado.
> You may see my paper for more details about the termination of loops:
> http://net.pku.edu.cn/~cuibin/Papers/2016SIGMOD.pdf 
> 
> 
> Regards
> Xiaogang
> 
> 2016-11-11 3:19 GMT+08:00 Paris Carbone  >:
> 
>> Hi again Flink folks,
>> 
>> Here is our new proposal that addresses Job Termination - the loop fault
>> tolerance proposal will follow shortly.
>> As Stephan hinted, we need operators to be aware of their scope level.
>> 
>> Thus, it is time we make loops great again! :)
>> 
>> Part of this FLIP basically introduces a new functional, compositional API
>> for defining asynchronous loops for DataStreams.
>> This is coupled with a decentralized algorithm for job termination with
>> loops - along the lines of what Stephan described.
>> We are already working on the actual prototypes as you can observe in the
>> links of the doc.
>> 
>> Please let us know if you like (or don't like) it and why, in this mail
>> discussion.
>> 
>> https://docs.google.com/document/d/1nzTlae0AFimPCTIV1LB3Z2y-
>> PfTHtq3173EhsAkpBoQ
>> 
>> cheers
>> Paris and Fouad
>> 
>> On 31 Oct 2016, at 12:53, Paris Carbone > > kth.se >> wrote:
>> 
>> Hey Stephan,
>> 
>> Thanks for looking into it!
>> 
>> +1 for breaking this up, will do that.
>> 
>> I can see your point and maybe it makes sense to introduce part of scoping
>> to incorporate support for nested loops (otherwise it can’t work).
>> Let us think about this a bit. We will share another draft for a more
>> detail description of the approach you are suggesting asap.
>> 
>> 
>> On 27 Oct 2016, at 10:55, Stephan Ewen > > 

Re: [DISCUSS] FLIP-14: Loops API and Termination

[SHI Xiaogang]

Hi Paris

I have several concerns about the correctness of the termination protocol.
I think the termination protocol put an end to the computation even when
the computation has not converged.

Suppose there exists a loop context constructed by a OP operator, a Head
operator and a Tail operator (illustrated in Figure 2 in the first draft).
The stream only contains one record. OP will pass the record to its
downstream operators 10 times. In other words, the loop should iterate 10
times.

If I understood the protocol correctly, the following event sequence may
happen in the computation:
t1:  RS emits Record to OP. Since RS has reached the "end-of-stream", the
system enters into Speculative Phase.
t2:  OP receives Record and emits it to TAIL.
t3:  HEAD receives the UpdateStatus event, and notifies with an IDLE state.
t4. OP receives the UpdateStatus event from HEAD, and notifies with an
WORKING state.
t5. TAIL receives Record and emits it to HEAD.
t6. TAIL receives the UpdateStatus event from OP, and notifies with an
WORKING state.
t7. The system starts a new attempt. HEAD receives the UpdateStatus event
and notifies with an IDLE state.  (Record is still in transition.)
t8. OP receives the UpdateStatus event from HEAD and notifies with an IDLE
state.
t9. TAIL receives the UpdateStatus event from OP and notifies with an IDLE
state.
t10. HEAD receives Record from TAIL and emits it to OP.
t11. System puts an end to the computation.

Though the computation is expected to iterate 10 times, it ends earlier.
The cause is that the communication channels of MASTER=>HEAD and TAIL=>HEAD
are not synchronized.

I think the protocol follows the idea of the Chandy-Lamport algorithm to
determine a global state.
But the information of whether a node has processed any record to since the
last request is not STABLE.
Hence i doubt the correctness of the protocol.

To determine the termination correctly, we need some information that is
stable.
In timelyflow, Naiad collects the progress made in each iteration and
terminates the loop when a little progress is made in an iteration
(identified by the timestamp vector).
The information is stable because the result of an iteration cannot be
changed by the execution of later iterations.

A similar method is also adopted in Tornado.
You may see my paper for more details about the termination of loops:
http://net.pku.edu.cn/~cuibin/Papers/2016SIGMOD.pdf

Regards
Xiaogang

2016-11-11 3:19 GMT+08:00 Paris Carbone :

> Hi again Flink folks,
>
> Here is our new proposal that addresses Job Termination - the loop fault
> tolerance proposal will follow shortly.
> As Stephan hinted, we need operators to be aware of their scope level.
>
> Thus, it is time we make loops great again! :)
>
> Part of this FLIP basically introduces a new functional, compositional API
> for defining asynchronous loops for DataStreams.
> This is coupled with a decentralized algorithm for job termination with
> loops - along the lines of what Stephan described.
> We are already working on the actual prototypes as you can observe in the
> links of the doc.
>
> Please let us know if you like (or don't like) it and why, in this mail
> discussion.
>
> https://docs.google.com/document/d/1nzTlae0AFimPCTIV1LB3Z2y-
> PfTHtq3173EhsAkpBoQ
>
> cheers
> Paris and Fouad
>
> On 31 Oct 2016, at 12:53, Paris Carbone  kth.se>> wrote:
>
> Hey Stephan,
>
> Thanks for looking into it!
>
> +1 for breaking this up, will do that.
>
> I can see your point and maybe it makes sense to introduce part of scoping
> to incorporate support for nested loops (otherwise it can’t work).
> Let us think about this a bit. We will share another draft for a more
> detail description of the approach you are suggesting asap.
>
>
> On 27 Oct 2016, at 10:55, Stephan Ewen  @apache.org>> wrote:
>
> How about we break this up into two FLIPs? There are after all two
> orthogonal problems (termination, fault tolerance) with quite different
> discussion states.
>
> Concerning fault tolerance, I like the ideas.
> For the termination proposal, I would like to iterate a bit more.
>
> *Termination algorithm:*
>
> My main concern here is the introduction of a termination coordinator and
> any involvement of RPC messages when deciding termination.
> That would be such a fundamental break with the current runtime
> architecture, and it would make the currently very elegant and simple model
> much more complicated and harder to maintain. Given that Flink's runtime is
> complex enough, I would really like to avoid that.
>
> The current runtime paradigm coordinates between operators strictly via
> in-band events. RPC calls happen between operators and the master for
> triggering and acknowledging execution and checkpoints.
>
> I was wondering whether we can keep following that paradigm and still get
> most of what you are proposing here. In some sense, all we need to do is
> replace RPC calls with