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In MPI, is it possible to add new nodes after it is started? For example, I have 2 computers already running a parallel MPI application. I start another instance of this application on a third computer and add it to the existing communicator. All computers are in a local network.

stokastik
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2 Answers2

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No, it's not currently possible to add new nodes to a running MPI application. MPI is designed to know the total number of nodes when the program starts.

Work is being done (on MPI-3, for example) on handling nodes that go down. Maybe if you can add faulty nodes back, then you can add new ones, but that's the closest thing I can think of. See this answer for more info on approaches to MPI fault tolerance.

Community
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Steve Blackwell
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It is possible for a MPI2 program to spawn new ranks. The function is MPI_Comm_spawn and it starts up children on a new MPI communicator. That is to say the new ranks have a different MPI_COMM_WORLD from the previously running ranks. It should be possible to make a new communicator that contains all of the current running ranks though.

qsc
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  • I think this is true for already-connected nodes, but not for external, new-to-comm-world nodes. – ivotron Jul 17 '13 at 21:06