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[netCDF #VIG-404579]: caching

Hi Reiner,

Sorry to have taken so long to respond to your question:
> I am making progress using netcdf4 on Linux and I am thinking of
> implementing a cache mechanism to avoid retrieving the same data twice over
> the Internet. I would like this cache to live-on between sessions and
> accumulate all accessed data in all sessions connected to a given nc file.
> Of course, the cache contents would have to be discarded when the nc file on
> the server side changes. Now I am wondering whether a netCDF/OpenDAP client
> has any way of retrieving version or file time stamp information of the
> remote data set. Comments and suggestions are greatly appreciated.

No sorry, I know no way of getting version or time stamp information unless
it is part of the metadata or data in the file you are accessing.

In general, there may not be a single file associated with the information 
returned
from an OPeNDAP query.  For example, if you request information from a TDS
server via DAP protocols, the response may require opening and aggregating data
and metadata from multiple files, which may span a wide range of times.

Since OPeNDAP protocols are layered on top of HTTP, you may be able to use 
information
in the HTTP header, but that's not available through the netCDF OPeNDAP client. 
 For
more information about this approach, see the DAP 2.0 standard, section 7.1.4, 
"Support
for HTTP/1.1 caching":

  http://opendap.org/pdf/ESE-RFC-004v1.1.pdf

There may be something more up-to-date on OPeNDAP support for caching, but I'm 
not aware
of it.  I'm Cc:ing Dennis Heimbigner, the Unidata expert on OPeNDAP client and 
server
protocols.  He can correct any misstatements I've made and may have more to add 
about
how you could tackle this problem.

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: VIG-404579
Department: Support netCDF
Priority: High
Status: Closed