Re: Large files access time

[Steve Hankin <Steven.C.Hankin@xxxxxxxx>]

Hi Jon,

a small P.S.:
Ferret has a qualifier USE/REGULAR_T (I think ...I'm offline at the moment)
that has the same effect as inserting the point-spacing='regular' attribute
on the T axis, but requires no change to the file.

    - steve

================================

Jonathan Callahan wrote:

> Jean-Marie,
>
> This seems inordinately slow for Ferret.  Especially for a file that is
> only 1.5 Mb!  When this happens it usually means that the time axis is
> marked as 'irregular' which means that Ferret has to read in the entire
> time axis before it can begin.  We have found many cases where the axis
> was actually 'regular' in spite of what the NetCDF attribute says.  If
> this is the case then you can use ncatted to change the time axis
> attribute and Ferret should open this dataset much more quickly.
>
> -- Jon
>
> J-M Epitalon wrote:
>
> >hello,
> >
> >I have daily simulation output covering the period 01-01-1950 to
> >31-12-2005. It is in a NetCDF file that is 1.5 Mb large.
> >
> >When I access it through Ferret, it takes 2 to 4 mn to open it (execute
> >instruction "use").
> >
> >I read in NCO documentation that "Some random access operations on large
> >files on certain architecture are slow when using the NetCDF interface".
> >
> >That seems to be the problem. I could check that it is slow also with
> >other tools than ferret (Python, or NCO tools).
> >
> >Anyway, what solution would you suggest to work around this ?
> >Is using MC descriptors a good idea?
> >
> >Thanks
> >
> >Jean-Marie Epitalon
> >CERFACS
> >Toulouse, France
> >
> >
> >