metadata consistency

[Wei-keng Liao]

One minor correction. The last API in the list I intent to say
is the family of ncmpi_put_att_<type> APIs. The <type> can be one
of text, uchar, schar, short, int, ...

Wei-keng

On Jul 11, 2013, at 12:03 PM, Wei-keng Liao wrote:

> Dear PnetCDF users,
> 
> I am working on strengthening the PnetCDF's metadata consistency and
> would like to change/limit the usage of APIs that modified the
> metadata (file header) of a netCDF file. These APIs are:
>    ncmpi_rename_dim(),
>    ncmpi_rename_var(),
>    ncmpi_copy_att(),
>    ncmpi_rename_att(), and
>    ncmpii_put_att().              <------- correction !
> 
> (The consistency here is referring to the consistency of file header
> data stored in memory across all MPI processes.)
> 
> In netCDF, the above APIs are allowed in data mode if the space
> required to store the new metadata (attributes, names, etc.) is
> less than the old one. Otherwise, they must be called in the define
> mode.
> 
> In PnetCDF, I would like to change that to allow these APIs only
> in define mode. If your applications require the above APIs to
> be called in data mode, please do let me know.
> 
> Here is my reason for the above change. In data mode, if metadata
> is changed on one process's memory (or even the change is written
> to the file by that process because NC_SHARE is set), there is no
> way to propagate the change from this process to other processes,
> until ncmpi_close() or ncmpi_sync() is called. If allowing these
> APIs in define mode only, we can rely on ncmpi_endef() to
> ensure/check the consistency.
> 
> Please let me know if your applications will have a problem with
> such change.
> 
> (My plan is to make NC_SHARE the default mode for PnetCDF as
> PnetCDF IS developed to handle parallel access to shared files.
> The above suggested API changes is the first step of my plan.)
> 
> 
> Wei-keng
>