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From Fabian Hueske <fhue...@gmail.com>
Subject Re: Implementing a low level join
Date Thu, 15 Aug 2019 07:58:59 GMT
Hi Felipe,

No, this is not possible (with reasonable effort).
A checkpoint would be the right time to do the change, but this would be
very involved, IMO.
As I said, you need a global decision to switch the strategy. This could be
communicated with a checkpoint barrier.
Then all operator would need to read (parts of) their state and ship it to
the other tasks, i.e., you need to exchange data between tasks of the same
operator.
There is no built-in tooling for this in Flink, so you would need to do
that yourself via some network connections. The coordination and timing
wouldn't be easy.

Something that might be a little bit easier could be to take a savepoint,
rewrite it with the new State Processor API, and load it into the updated
job.
This wouldn't be a real online switch, but might be good enough and does
not require distributed coordination.

Cheers,
Fabian

Am Do., 15. Aug. 2019 um 09:50 Uhr schrieb Felipe Gutierrez <
felipe.o.gutierrez@gmail.com>:

> Hi Fabian,
>
> thanks for jumping within this thread.
> Do you think there is possible to extend any join generic operator in
> order to make it a little dynamic? I was thinking that after I process a
> checkpoint I can change the join strategy.
>
> and if you do, do you have any toy example of this?
>
> Thanks,
> Felipe
> *--*
> *-- Felipe Gutierrez*
>
> *-- skype: felipe.o.gutierrez*
> *--* *https://felipeogutierrez.blogspot.com
> <https://felipeogutierrez.blogspot.com>*
>
>
> On Thu, Aug 15, 2019 at 9:42 AM Fabian Hueske <fhueske@gmail.com> wrote:
>
>> Hi,
>>
>> Just to clarify. You cannot dynamically switch the join strategy while a
>> job is running.
>> What Hequn suggested was to have a util method Util.joinDynamically(ds1,
>> ds2) that chooses the join strategy when the program is generated (before
>> it is submitted for execution).
>>
>> The problem is that distributed joins are composed of a data distribution
>> strategy (Broadcast-Forward, Partitioning) and a local execution strategy
>> (Hybrid Hash, Symmetric Hash, Nested Loops, Sort Merge, ...).
>> Switching the local strategy is sometimes possible but changing the data
>> distribution strategy is much more involved because you'd need global
>> coordination and re-distribute the data.
>>
>> Best,
>> Fabian
>>
>> Am Do., 15. Aug. 2019 um 09:31 Uhr schrieb Felipe Gutierrez <
>> felipe.o.gutierrez@gmail.com>:
>>
>>> I see, I am gonna try this.
>>> Thanks Hequn
>>> *--*
>>> *-- Felipe Gutierrez*
>>>
>>> *-- skype: felipe.o.gutierrez*
>>> *--* *https://felipeogutierrez.blogspot.com
>>> <https://felipeogutierrez.blogspot.com>*
>>>
>>>
>>> On Thu, Aug 15, 2019 at 4:01 AM Hequn Cheng <chenghequn@gmail.com>
>>> wrote:
>>>
>>>> Hi Felipe,
>>>>
>>>> If I understand correctly, you also have to decide whether to broadcast
>>>> the datastream from the right side before performing the function?
>>>>
>>>> One option is you can add a Util method to join dynamically, e.g.,
>>>> Util.joinDynamically(ds1, ds2). In the util method, you can implement your
>>>> own strategy logic and decide whether to broadcast or use CoProcessFunction.
>>>>
>>>> Best, Hequn
>>>>
>>>> On Wed, Aug 14, 2019 at 3:07 PM Felipe Gutierrez <
>>>> felipe.o.gutierrez@gmail.com> wrote:
>>>>
>>>>> Hi Hequn,
>>>>>
>>>>> I am implementing the broadcast and the regular join. As you said I
>>>>> need different functions. My question is more about if I can have an
>>>>> operator which decides beteween broadcast and regular join dynamically.
I
>>>>> suppose I will have to extend the generic TwoInputStreamOperator in Flink.
>>>>> Do you have any suggestion?
>>>>>
>>>>> Thanks
>>>>>
>>>>> On Wed, 14 Aug 2019, 03:59 Hequn Cheng, <chenghequn@gmail.com>
wrote:
>>>>>
>>>>>> Hi Felipe,
>>>>>>
>>>>>> > I want to implement a join operator which can use different
>>>>>> strategies for joining tuples.
>>>>>> Not all kinds of join strategies can be applied to streaming jobs.
>>>>>> Take sort-merge join as an example, it's impossible to sort an unbounded
>>>>>> data. However, you can perform a window join and use the sort-merge
>>>>>> strategy to join the data within a window. Even though, I'm not sure
it's
>>>>>> worth to do it considering the performance.
>>>>>>
>>>>>> > Therefore, I am not sure if I will need to implement my own
>>>>>> operator to do this or if it is still possible to do with CoProcessFunction.
>>>>>> You can't implement broadcast join with CoProcessFunction. But you
>>>>>> can implement it with BroadcastProcessFunction or
>>>>>> KeyedBroadcastProcessFunction, more details here[1].
>>>>>>
>>>>>> Furthermore, you can take a look at the implementation of both window
>>>>>> join and non-window join in Table API & SQL[2]. The code can
be found
>>>>>> here[3].
>>>>>> Hope this helps.
>>>>>>
>>>>>> Best, Hequn
>>>>>>
>>>>>> [1]
>>>>>> https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/broadcast_state.html
>>>>>> [2]
>>>>>> https://ci.apache.org/projects/flink/flink-docs-release-1.8/dev/table/sql.html#joins
>>>>>> [3]
>>>>>> https://github.com/apache/flink/tree/master/flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/runtime/join
>>>>>>
>>>>>>
>>>>>> On Tue, Aug 13, 2019 at 11:30 PM Felipe Gutierrez <
>>>>>> felipe.o.gutierrez@gmail.com> wrote:
>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I want to implement a join operator which can use different
>>>>>>> strategies for joining tuples. I saw that with CoProcessFunction
I am able
>>>>>>> to implement low-level joins [1]. However, I do know how to decide
between
>>>>>>> different algorithms to join my tuples.
>>>>>>>
>>>>>>> On the other hand, to do a broadcast join I will need to use
the
>>>>>>> broadcast operator [2] which yields a BroadcastStream. Therefore,
I am not
>>>>>>> sure if I will need to implement my own operator to do this or
if it is
>>>>>>> still possible to do with CoProcessFunction.
>>>>>>>
>>>>>>> Does anyone have some clues for this matter?
>>>>>>> Thanks
>>>>>>>
>>>>>>> [1]
>>>>>>> https://ci.apache.org/projects/flink/flink-docs-release-1.8/dev/stream/operators/process_function.html#low-level-joins
>>>>>>> [2]
>>>>>>> https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/broadcast_state.html
>>>>>>> *--*
>>>>>>> *-- Felipe Gutierrez*
>>>>>>>
>>>>>>> *-- skype: felipe.o.gutierrez*
>>>>>>> *--* *https://felipeogutierrez.blogspot.com
>>>>>>> <https://felipeogutierrez.blogspot.com>*
>>>>>>>
>>>>>>

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