Unchecked memory allocation and potential performance problem

[Russ Rew]

On Wed, Dec 06, 2006 at 09:53:18 -0600, Rob Latham wrote:
> Off the top of my head there are two not-too-hard ways we can do this:
> 
> There's nothing in the CDF-1 or CDF-2 file format spec that prevents
> us from using an arbitrarily large header to describe the data.  If we
> know the right parameters for alignment and blocksize, we can pad the
> header out to a useful point (which might somewhat reduce the chance a
> re-definition would trigger a costly data shuffle).
> 
> Same thing for variables.  We don't *have* to place variables butting
> up against each other.  They could also be padded out to beneficial
> points in the file.  This change would be more invasive than padding
> the header.

There is a documented serial netCDF-3 interface for reserving extra
space in the header and for controlling alignment of the data sections
for fixed-size and record variables, using the function nc__enddef
(note the two underscores in the name):

  http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-c.html#nc_005f_005fenddef

Also by default, data for variables starts on four-byte boundaries, so
badly aligned accesses should not occur except possibly when getting
subsets of byte or short variables.

--Russ