[EMAIL PROTECTED] wrote on Mon, 09 Oct 2006 10:57 -0500:
> I'm warming to the idea of doing everything related to distributions
> through the hints mechanism, even though it sort of undoes Pete's
> attempt to simplify the discussion.
My number one complaint with using a hint mechanism is that it is a
direct indication that the API was poorly designed in the first
place.
An exception to this rule is to implement purely optional parameters
for performance optimization, like most of the hints applied to
MPI_File_open. The code still works without these hints, just
slower.
Like Walt, I'm also not real clear on why anybody needs to specify
hostnames as well as a distribution when creating a file. But the
discussion I've seen makes it look like people who want to do this
do not view the hostname placement rules as optional. If PVFS
ignores the hint, that is definitely not okay. So it should be part
of the API proper if we take it seriously.
I don't care much about passing strings versus passing arrays of
keyvals, but I don't want to have a whole set of different knobs
to control what are conceptually part of the same function: how do
the bytes of the file get laid out on disks.
> So I think we're mostly trying to work out what our API should really
> be, whether we should extend the distro functionality vs. going totally
> to hints, and if we go to hints what that API should look like, right?
Yes. Pick one. If you want to augment the existing PVFS_sys_dist
set of calls (lookup, setparam, ...) to handle hostnames, fine. If
you want to scrap all that and go with a big opaque string passed
into PVFS_sys_create, that would be another approach, but let's not
do both. (And not call the string a "hint" if it is mandatory.)
How about just add PVFS_sys_dist_get_IO_server_aliases() and
PVFS_sys_dist_set_IO_server_mapping(). Under the hood each
distribution orders the IO servers it'll use according to the
mapping then does business as usual. This instead of the random
starting point and sequential ordering used now.
-- Pete
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