[mpich-discuss] romio large array

[Rob Latham]

On Mon, Apr 26, 2010 at 08:05:41AM -0500, Dave Goodell wrote:
> [adding RobL]
> 
> It looks like ROMIO is checking for reads of more data than INT_MAX
> bytes in a single call.  I'm guessing that this is defensive because
> some of the internal code in ROMIO may not be prepared to handle
> this case.  Rob can probably comment with less speculation.

that's exactly what's going on.  

Dave, I don't know if the forum is still talking about the MPI_COUNT
issue, but we get questions like this about once a year. People
definitely try to read more than 2GB of data at a time.

> The best workaround is probably to split the read into two reads for
> now.

Yep.  Try to decompose it so that the data remains contiguous in
memory. It's a bit of a pain to program, but you'll likely not see any
decrease in performance.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA