Re: Bug#961108: openmpi: providing 64-bit MPI

[Gard Spreemann <gspr@nonempty.org>]

Drew Parsons <dparsons@debian.org> writes:

> If I understand correctly, it's dangerous to simply enable 64-bit in
> PETSc alone. It needs to be done all along the computational library
> stack.

In the case of PETSc, is the intention to change to using the 64-bit
indexing option, or to provide a new additional package that uses 64-bit
indexing? The latter sounds burdensome long-term, so I would probably
lean towards the former.

If you do intend to go for the former, I think it's a good idea to very
clearly warn the user upon upgrade. The PETSc binary sparse matrix and
vector file formats are assumed to use whatever indexing data types that
the library is compiled with, and as far as I remember there is no
metadata about this in the file format itself. Without warning, I
suspect a lot of users might burn themselves when using LoadMat [1] and
friends on data files written with 32 bit index versions of the
package. I don't know how common the file format is and whether most
people just use HDF5, but I know I've often used the PETSc format to
avoid the complications of HDF5.

PS: I can volunteer to write a 32->64 bit conversion tool for these
files if desired. Ideally I guess upstream should provide 32/64-bit
specific versions of the reading/writing functions.

[1] https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatLoad.html


 Best,
 Gard