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HDFS, mail # user - Re: Chaning Multiple Reducers: Reduce -> Reduce -> Reduce


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Re: Chaning Multiple Reducers: Reduce -> Reduce -> Reduce
Edward J. Yoon 2012-10-08, 22:47
P.S., giraph is different in the sense that it runs as a map-only job.

On Tue, Oct 9, 2012 at 7:45 AM, Edward J. Yoon <[EMAIL PROTECTED]> wrote:
>> asking for. If anyone who used Hama can point a few articles about how
>> the framework actually works and handles the messages passed between
>> vertices, I'd really appreciate that.
>
> Hama Architecture:
> https://issues.apache.org/jira/secure/attachment/12528219/ApacheHamaDesign.pdf
>
> Hama BSP programming model:
> https://issues.apache.org/jira/secure/attachment/12528218/ApacheHamaBSPProgrammingmodel.pdf
>
> On Tue, Oct 9, 2012 at 4:09 AM, Jim Twensky <[EMAIL PROTECTED]> wrote:
>> Thank you for the comments. Some similar frameworks I looked at
>> include Haloop, Twister, Hama, Giraph and Cascading. I am also doing
>> large scale graph processing so I assumed one of them could serve the
>> purpose. Here is a summary of what I found out about them that is
>> relevant:
>>
>> 1) Haloop and Twister: They cache static data among a chain of
>> MapReduce jobs. The main contribution is to reduce the intermediate
>> data shipped from mappers to reducers. Still, the output of each
>> reduce goes to the file system.
>>
>> 2) Cascading: A higher level API to create MapReduce workflows.
>> Anything you can do with Cascading can be done practically by more
>> programing effort and using Hadoop only. Bypassing map and running a
>> chain of sort->reduce->sort->reduce jobs is not possible. Please
>> correct me if I'm wrong.
>>
>> 3) Giraph: Built on the BSP model and is very similar to Pregel. I
>> couldn't find a detailed overview of their architecture but my
>> understanding is that your data needs to fit in distributed memory,
>> which is also true for Pregel.
>>
>> 4) Hama: Also follows the BSP model. I don't know how the intermediate
>> data is serialized and passed to the next set of nodes and whether it
>> is possible to do a performance optimization similar to what I am
>> asking for. If anyone who used Hama can point a few articles about how
>> the framework actually works and handles the messages passed between
>> vertices, I'd really appreciate that.
>>
>> Conclusion: None of the above tools can bypass the map step or do a
>> similar performance optimization. Of course Giraph and Hama are built
>> on a different model - not really MapReduce - so it is not very
>> accurate to say that they don't have the required functionality.
>>
>> If I'm missing anything and.or if there are folks who used Giraph or
>> Hama and think that they might serve the purpose, I'd be glad to hear
>> more.
>>
>> Jim
>>
>> On Mon, Oct 8, 2012 at 6:52 AM, Michael Segel <[EMAIL PROTECTED]> wrote:
>>> I don't believe that Hama would suffice.
>>>
>>> In terms of M/R where you want to chain reducers...
>>> Can you chain combiners? (I don't think so, but you never know)
>>>
>>> If not, you end up with a series of M/R jobs and the Mappers are just identity mappers.
>>>
>>> Or you could use HBase, with a small caveat... you have to be careful not to use speculative execution and that if a task fails, that the results of the task won't be affected if they are run a second time. Meaning that they will just overwrite the data in a column with a second cell and that you don't care about the number of versions.
>>>
>>> Note: HBase doesn't have transactions, so you would have to think about how to tag cells so that if a task dies, upon restart, you can remove the affected cells.  Along with some post job synchronization...
>>>
>>> Again HBase may work, but there may also be additional problems that could impact your results. It will have to be evaluated on a case by case basis.
>>>
>>>
>>> JMHO
>>>
>>> -Mike
>>>
>>> On Oct 8, 2012, at 6:35 AM, Edward J. Yoon <[EMAIL PROTECTED]> wrote:
>>>
>>>>> call context.write() in my mapper class)? If not, are there any other
>>>>> MR platforms that can do this? I've been searching around and couldn't
>>>>
>>>> You can use Hama BSP[1] instead of Map/Reduce.
>>>>
>>
Best Regards, Edward J. Yoon
@eddieyoon