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From Benoît Hanotte <benoit.jc.hano...@campus.tu-berlin.de>
Subject Re: Nested Iterations supported in Flink?
Date Tue, 14 Apr 2015 13:53:21 GMT
Thanks for you quick answers!

The algorithm is the following: I've got a spatial set of data and I want  
to find dense regions. The space is beforehand discretized into "cells" of  
a fixed size. Then, for each dense cell (1st iteration), starting with the  
most dense, the algorithm tries to extend it with neighboring cells (the  
nested iteration) until the density of the obtained extended cell is under  
a threshold (and some other conditions). When that's done, the used cells  
are removed from the input set, and the next most dense cell is extended.

Would running the program multiple times be efficient in that case (I  
would have to save the datasets and reload them probably)? As for using  
the mapPartition operator I think it wouldn't be possible since the nested  
iteration needs the entire cells datasets.

Best,

Benoît



Le Tue, 14 Apr 2015 15:16:48 +0200, Till Rohrmann  
<till.rohrmann@gmail.com> a écrit:

> If your inner iterations happens to work only on the data of a single  
> partition, then you can also implement this iteration as part >of a  
> mapPartition operator. The only problem there would be that you have to  
> keep all the partition's data on the heap, if you >need access to it.
>
> Cheers,
>
> Till
>
> On Tue, Apr 14, 2015 at 3:11 PM, Stephan Ewen <sewen@apache.org> wrote:
>> Hi Benoît!
>>
>> You are right, the nested iterations are currently not supported.
>>
>> The test you found actually checks that the Optimizer gives a good  
>> error message when encountering nested iterations.
>>
>> Can you write your program as one iterations (the inner) and start the  
>> program multiple times to simulate the nesting?
>>
>> Greetings,
>> Stephan
>>
>>
>> On Tue, Apr 14, 2015 at 8:11 AM, Benoît Hanotte  
>> <benoit.jc.hanotte@campus.tu-berlin.de> wrote:
>>> Hello,
>>>
>>> I'm implementing an algorithm which requires nested iterations, and,  
>>> from what I understood, this feature was not yet >>>available in Flink
 
>>> [1], and my experiments with 2 nested bulk iterations seem to confirm  
>>> that. However I came across a >>>Flink unit test [2] using nested  
>>> iterations, so I'm now a bit confused. Could you please give me some  
>>> insight on what is >>>supported or not in the current state of the 

>>> project?
>>>
>>> Thanks!
>>>
>>> Benoît.
>>>
>>> [1]  
>>> http://mail-archives.apache.org/mod_mbox/flink-user/201411.mbox/%3CCANC1h_tpNFWwrnm14+Et1yBvkQPQ1->>>pfk=iUPP5Un90ZgUGeyg@mail.gmail.com%3E
>>> [2]  
>>> https://github.com/apache/flink/blob/master/flink-optimizer/src/test/java/org/apache/flink/optimizer/>>>NestedIterationsTest.java
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