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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
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Hi Heiko, In THREDDS, we have some support for Last-Modified just not in all the services we support (for various reasons). It is a bit more complicated to get an accurate last-modified date for aggregated (and other virtual) datasets but certainly do-able. John Caron is reworking some of the TDS aggregation code so I'll talk to him about support for last-modified times there. Jon has done some ncWMS refactoring and I'm working on folding that into the TDS. I think this might fit into that work as well. He and I will talk off line and see what we can come up with. Cheers, Ethan On 2/17/2010 7:22 AM, Heiko Klein wrote: > Hi Jon, > > I made a mistake while testing. The png-elements returned from ncWMS > don't have a no-cache or expires response-header, only the > getCapabilites document does so. > > I've been checking the png-headers with firebug, and it was firebug > which added a no-cache element and pragma to the request-header. And > this made panning around in a figure very slow. Disabling firebug > reduced the wms-server load a lot. > > Nonetheless, a static configuration parameter as you suggest would be > nice. Another option (or maybe in addition) could be to add the > Last-Modified Date to the response header ( > http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.3.1 ). > > Best regards, > > Heiko > > On 2010-02-17 12:17, Jonathan Blower wrote: >> Hi Heiko, >> >> Cache control is tricky as there is always a danger that cached images >> can hang around while the backing data changes. Hence THREDDS is very >> conservative. ncWMS has more sophisticated caching than THREDDS, for >> various technical reasons, but this is implemented at the server side, >> rather than using http expiration controls. >> >> It might be possible to have a configuration parameter that enables the >> sysadmin to set the expiration time for images from a particular server >> (or maybe a particular dataset). Would this be useful? Even a figure >> of 1 or 5 minutes would help a browser to cache in the case of panning >> around a figure. >> >> Cheers, Jon >> >> -----Original Message----- >> From: Heiko Klein [mailto:Heiko.Klein@xxxxxx] >> Sent: 15 February 2010 16:33 >> To: thredds@xxxxxxxxxxxxxxxx >> Cc: Jonathan Blower >> Subject: Cache-Control in ncWMS/Thredds >> >> Hi, >> >> while trying to get the ncWMS/Thredds operational, I recognized that all >> elements (png/getCapabilities) are returned with an expiration date = >> Expires Thu Jan 01 1970 01:00:00 GMT+0100 (CET) >> >> This generates a high load on our server, since the browser refetches >> each tile while looking around the figure. Is it possible to control the >> browser-cache for ncWMS/Thredds? >> >> Best regards, >> >> Heiko > > _______________________________________________ > thredds mailing list > thredds@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/
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