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From Alexandros Daglis <alexandros.dag...@epfl.ch>
Subject Re: Inter- and intra-node message passing
Date Mon, 04 Feb 2013 20:30:09 GMT
This helps indeed. Thank you Claudio!

Alexandros

On 4 February 2013 18:48, Claudio Martella <claudio.martella@gmail.com>wrote:

> Giraph runs on a Hadoop cluster as a map reduce job. Each worker is hence
> a different task and it runs as a different jvm. This means that you can
> have two workers running in the same machine. Hence it can happen that two
> vertices running on two different workers executed in the same machine
> might exchange messages over the network. The practical impact depends on
> the host operating system.
> On the other side, two vertices residing on the same worker but being
> computed by different compute threads will behave as mentioned in the
> previous email. If you would like to minimize the first behavior, you
> should ensure a single worker is executed on each machine, and set
> adequately the number of compute threads per worker.
>
> Hope this helps,
> Claudio
>
>
> On Monday, February 4, 2013, Daglis Alexandros wrote:
>
>>  Hello Claudio,
>>
>> Thank you for your prompt answer!
>> So, vertices that belong to the same worker thread do not require access
>> to the network in order to exchange messages.
>> However, what about *different worker threads* that reside on different
>> cores *of the same node*?
>>
>> Cheers,
>> Alexandros
>>
>>  ------------------------------
>> *From:* Claudio Martella [claudio.martella@gmail.com]
>> *Sent:* Monday, February 04, 2013 6:19 PM
>> *To:* user@giraph.apache.org
>> *Subject:* Re: Inter- and intra-node message passing
>>
>>   Hi Alexandros,
>>
>>  if two vertices are on the same worker, the message does not pass
>> through the network but it is put directly in the mailbox of the
>> destination vertex.
>>
>>  Cheers,
>> Claudio
>>
>>
>> On Mon, Feb 4, 2013 at 6:03 PM, Alexandros Daglis <
>> alexandros.daglis@epfl.ch> wrote:
>>
>>>  Hello everybody,
>>>
>>> I was wondering about the message-passing protocol: is there a
>>> difference if two communicating threads are on the same node, as opposed to
>>> being on different ones? Is communication achieved through memory whenever
>>> the threads are local to the node, or does it always default to the
>>> network?
>>>
>>> I tried answering that question by going through the code, but I haven't
>>> seen any high-level difference in handling those two different cases. I
>>> would appreciate if someone could give me a hint on that.
>>>
>>> Thank you in advance.
>>> Alexandros
>>>
>>
>>
>>
>>  --
>>    Claudio Martella
>>    claudio.martella@gmail.com
>>
>
>
> --
>    Claudio Martella
>    claudio.martella@gmail.com
>

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