Hi Mark,
On Jul 8, 2010, at 11:07 AM, Mark Howison wrote:
> Hi all,
>
> I'm wondering what happens internally in parallel HDF5 when two or
> more procs have overlapping hyperslab selections, e.g. when each proc
> has a layer of ghost zones for a stencil calculation and it tries to
> write all of the data including the ghost zones.
>
> Does HDF5 issue redundant read/write requests for the elements in the
> overlapping region? Or does it try to shrink the regions until they
> are disjoint? In the MPI-IO VFD, will the behavior depend on
> collective vs. independent mode?
The HDF5 library doesn't check for overlapping selections and the
behavior is dependent on the timing of the I/O operations (for serial and
parallel independent I/O) and whatever the MPI library does (for parallel
collective I/O), but the MPI standard says that this operation's outcome is
undefined (and thus will likely be subject to timing or process ordering
issues).
Quincey
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