[petsc-dev] use of hash table vs array in various places in PETSc

[Jed Brown]

On Wed, Sep 21, 2011 at 15:25, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
> >   Look at the MPI 3 proposals.
> >
> > The neighborhood collectives are the most natural mapping of VecScatter
> to MPI, but creation is still not as convenient.
>
>
>     Then they are fucking up MPI-3 and don't know what they are doing. Why
> not propose to them the correct model?
>

https://svn.mpi-forum.org/trac/mpi-forum-web/attachment/ticket/258/topol.pdf

You can see the proposal here, skip ahead to page 24, the red text is new.

There is no persistent non-blocking operation and setup involves creating a
communicator with graph topology and then having the user hold the send and
receive buffers. This is fine for implementing our scatter (though I'd
prefer a persistent variant), but our scatter is at a much higher level. I
don't think it belongs in MPI proper, at least not at this time, and suspect
there is little to no hope of getting it in the standard this late even if
we had a complete working implementation and full proposal ready for review
today.

Perhaps it could go in a thin library on top of MPI, but with no PETSc
dependencies.
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