[mpich-discuss] How does hyday works?

[Balaji, Pavan]

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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