Summary of today's meeting

Hello Rich,

I thought it was also agreed that if process A communicates with failed process B
which had been restarted by another process C, and this was the first communication
from A to B since the restart of B, A would receive the equivalent of a ECONNRESET error.
This was in the context of a case where option 5 below is not being used by the app.

Howard

Richard Graham wrote:

Summary of today's meeting Here is a summary of what I think that we agreed to today. Please correct any errors, and add what I am missing.

We need to be able to restore MPI_COMM_WORLD (and it’s derivatives) to a usable state when a process fails.

Restoration may involve having MPI_PROC_NULL replace the lost process, or may replaced the lost processes with a new process (have not specified how this would happen)

Processes communicating directly with the failed processes will be notified via a returned error code about the failure.

When a process is notified of the failure, comm_repair() must be called. Comm_repair() is not a collective call, and is what will initiate the communicator repair associated with the failed process.

If a process wants to be notified of process failure even if it is not communicating directly with this process, it must register for this notification.

We don’t have enough information to know how to continue with support for checkpoint/restart.

We need to discuss what needs to do with respect to failure of collective communications.

There are several issues that came up with respect to these, which will be detailed later on.

Rich
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Howard Pritchard 
Cray Inc.