Hi Tim, unfortunately I have no influence on the servers I get my images from.
THX Carsten Am 04.03.2010 20:06, schrieb Tim Schaub: > Hey- > > Dipl. Inf. Carsten Eider wrote: > >> Hi list, >> >> while examining my WMS-Servers logs i was surpprised by the amount of >> WMS-requests I found within. >> Using Firefox and Firebug i recognized, that the tiles were not cached >> by the browser, i.e. >> each time they came into the viewport of the map they were re-requested! >> >> Is there a way to use cached images by the browser instead of requesting >> them time and again? >> >> > Caching is best controlled by using the appropriate headers in your > server responses. > > If your server responds with an Expires header, we can't force the > browser to use a cached image (without essentially rewriting our own > cache) if the Expires date has been reached. > > If your server (or gateway cache) uses Etag or Last-Modified headers, > the browser will try to make requests with If-None-Match or > If-Modified-Since headers. If the server responds with 304, Not > Modified, the browser will pull from its cache. > > Looking at the http://openlayers.org/dev/examples/example.html example, > you can see Etag headers on the static images (west-mini.png etc.). The > GetMap responses from openlayers.org contain Expires headers > corresponding to the request time (so they immediately expire). The > GetMap responses from www2.dmsolutions.ca don't contain any cache > related headers. > > When you refresh the page, requests for static images return 304, Not > Modified, and the browser pulls those from its cache. Previous > responses for GetMap images make the browser think those should not be > cached, so they are requested with Cache-Control: max-age=0. We can't > override the headers in this case, so if your server obeys, it will do > whatever it does to generate new GetMap responses. > > So, you can improve the caching situation by having your server (or > gateway cache) use appropriate headers on responses. If you configure a > gateway cache like Varnish or Squid in front of your WMS, this should be > handled for you. If you use a tile generator to pre-seed a tile cache > and serve those statically, you can configure your server to use > Last-Modified headers. If you are confident that you won't be updating > static images, use future Expires headers to avoid the intermediate > request with If-None-Match or If-Modified-Since headers. > > The short story is that for image requests and effectively using the > browser's cache, OpenLayers isn't the place to make changes. > > Oh, and re-reading your question, I see you were talking about > panning/zooming instead of reloading the page. The same advice applies, > with the additional note that your browser cache can eventually fill up. > I think the default configuration for Firefox is 50MB. > > Hope that is some help. > Tim > > >> THX >> Carsten >> >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> Dev mailing list >> Dev@openlayers.org >> http://openlayers.org/mailman/listinfo/dev >> > > -- Mit freundlichen Grüßen / Yours faithfully Carsten Eider Dipl. Inf. (FH) Kompetenzzentrum für Innovative Informationssysteme c/o Fachhochschule Bingen / University of applied sciences Bingen Berlinstraße 109 55411 Bingen Tel: +49 (0) 6721 / 409-179 Fax: +49 (0) 6721 / 994-251 email: ei...@fh-bingen.de Internet: iis.fh-bingen.de Diese E-Mail, inklusive anhängender Dateien, kann vertrauliche und/oder rechtlich geschützte Inhalte enthalten. Wenn Sie nicht der richtige Adressat sind und diese E-Mail irrtümlich erhalten haben, benachrichtigen Sie bitte sofort den Absender und vernichten Sie sodann die Originalnachricht. Die unbefugte Kopie, Weiterleitung oder sonstige Verbreitung dieser Nachricht ist nicht gestattet. This e-mail, including attachments, may contain confidential and/or privileged information. If you are not the intended recipient, please notify the sender immediately then delete the original message. Any copying forwarding and/or distribution without permission of the sender is forbidden.
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