[mpich-discuss] How does hyday works?

[Balaji, Pavan]

It's a distributed service.

  -- Pavan

> On Feb 14, 2017, at 2:23 PM, Dorier, Matthieu <mdorier at anl.gov> wrote:
> 
> Is the key-value server located on the machine that ran mpiexec, or on one of the machine in the hostfile?
> Thanks,
> 
> Matthieu
> ________________________________________
> From: Balaji, Pavan [balaji at anl.gov]
> Sent: Tuesday, February 14, 2017 2:04 PM
> To: discuss at mpich.org
> Subject: Re: [mpich-discuss] How does hyday works?
> 
> Well, not exactly.  The environment variables tell MPICH how to connect to a key-value server.  Then each process puts its business card (e.g., IP address and port) into the key-value server and all processes can query this information for the target process they want to communicate with.
> 
>  -- Pavan
> 
>> On Feb 14, 2017, at 11:19 AM, Dorier, Matthieu <mdorier at anl.gov> wrote:
>> 
>> Hi,
>> 
>> I'd like to have a better understanding of how Hydra works and how MPI processes "discover" how to connect to one another. I'm guessing something roughly like this happens:
>> 
>> - mpiexec launches and ssh connection to each node, and sets some environment variables that will indicate to the created processes how to connect to one another;
>> - MPI processes are created, and when calling MPI_Init they read the right environment variables to build MPI_COMM_WORLD.
>> 
>> Is this correct? If so, where could I find information about the environment variables at play?
>> 
>> Thanks,
>> 
>> Matthieu
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