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
>
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