[EXTERNAL] Re: metadata consistency

[Rob Latham]

On Thu, Jul 18, 2013 at 11:47:57AM -0500, Wei-keng Liao wrote:
> There is an issue for flushing the number of records to file I would like
> discuss here. In r1364, since the number of records is part of file header,
> it is flushed to file only when NC_SHARE is used. Otherwise, it will be done
> at file close time. However, because flushing it only requires to write a
> 4-byte (CDF and CDF2) or 8-byte integer (CDF5), flushing it should cost
> much less than other header changes. Other cases will require to flush the
> entire header. I can change the flushing to be performed no matter
> NC_SHARE is set or not. Please let me know your preference on when the
> number of records should be flushed, as this can affect what you will
> see from the file header if the program stops/exists before file close.

As our HDF5 friends can attest, metadata consistency is a big deal. 

I'm nervous, though, about introducing an additional 8 byte write to
every record variable I/O operation.   I guess we should try it and
see what the costs are.  

==rob

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