Appreciate your answer.
Since I met some access performance problem, I need to know the details of
my netcdf file.
Is it possible to display compression level and chunk size by some existing
tools?
Since the file that I use is not generated by me, I need to check those very
detailed information.
Thanks
On Tue, Jul 19, 2011 at 6:04 PM, Russ Rew <russ@xxxxxxxxxxxxxxxx> wrote:
> Hi Chris,
>
> > Will the performance of access to NetCDF degrades if I set every
> dimension
> > unlimited?
>
> Short answer: yes.
>
> Explanation: when you make a dimension unlimited, variables that use
> that dimension use chunked storage rather than contiguous storage, which
> incurs some storage overhead for B-tree indexing of the resulting chunks
> and for partially written chunks.
>
> Also, variables that use unlimited dimensions use 1, by default, for the
> chunk length along unlimited dimension axes. That's a reasonable
> default for multidimensional variables that have only one unlimited
> dimension, but if all dimensions are unlimited, the default would make
> chunk sizes for all variables only big enough to hold 1 value, which
> would be a very inefficient use of chunking.
>
> If you specify chunk lengths explicitly for each variable, and if you
> intend to append an unknown amount of data along every dimension, it may
> make sense to set every dimension unlimited. Otherwise, it would be
> better to only declare a few dimensions unlimited, those along which
> data will be appended.
>
> --Russ
>
