Re: [thredds] Cache-Control in ncWMS/Thredds

• To: Jonathan Blower <j.d.blower@xxxxxxxxxxxxx>
• Subject: Re: [thredds] Cache-Control in ncWMS/Thredds
• From: Heiko Klein <Heiko.Klein@xxxxxx>
• Date: Wed, 17 Feb 2010 15:22:25 +0100

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

• Follow-Ups:
  • Re: [thredds] Cache-Control in ncWMS/Thredds
    • From: Ethan Davis

• References:
  • [thredds] Cache-Control in ncWMS/Thredds
    • From: Heiko Klein
  • Re: [thredds] Cache-Control in ncWMS/Thredds
    • From: Jonathan Blower