Hi,
> The server-settable-dist would be implemented to store the indices
> for the IO servers in the params field of the PVFS_sys_dist
> structure. I used server indices, because the PINT_dist_* interfaces
> allow for that (through the PINT_request_file_data struct), but its a
> bit ugly and probably confusing to the user. We could change that
> though, and use something like server aliases or hostnames, passing
> them through to the distribution parameters instead of indices. This
> would require a change to the distribution method calls, and the
I see what you mean, but that is certainly more efford and not useful for the
majority of the users. I think new functionality like the setting of the
hosts can be tested easily with the hint mechanisms and once they are used
more frequently during calls the interfaces can adapt it...
If the parameters are stored in the dist parameters like you suggest that will
be a problem for the migration and changed dataservers. Also it will not
allow to set the servers for all distributions...
> Right, I don't like the idea of 'overriding' a distribution's
> behavior with a hint. Conceptually it seems like the distribution
> should take care of this, and if it doesn't, we should fix it so it
> does.
I agree completely with that one :)
> Also, the server list hint gets a little ugly across sysint calls,
> since the list doesn't actually get stored anywhere for that file
> (does it?). With the distribution, we only have to specify it once
> at creation time, instead of passing it along to all future IO calls
> on that file.
It is not necessary to store it explicitly, even with the hint it has to be
specified only during the creation like you propose. Then it chooses the
datafile servers depending on the names, create dfiles only on those and sets
the datafile_array for the metafile later according to that list. Thus the
information is stored outside of the distribution. This is very useful for my
migration and also works on all distributions.
To come back to the hint struct, I would prefer this one:
typedef struct
{
char * type; /* null terminated */
char * hint; /* null terminated */
} PVFS_hint;
I do not see the usefulness of letting the user specify a non null terminated
hint, users/researchers propably will use something like that to cast an
arbitrary structure into the hint field, which is problematic for
compatibilty with other architectures.
Thanks,
Julian
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