Hi,

I have a typical setup like:

PostGIS => GS => GWC => Browser.


Can I have preseeded tiles at GeoWebCache that are invalidated (i.e. get 
expired) on the fly based on caching headers?

That is, is the following possible?:

1. Browser re-requests a certain tile including If-Modified-Since header
2. GWC has a preseeded tile but needs to know if the tile is still valid. So 
GWC passes the request (still with If-Modified-Since) on to GS
3. GS looks up PostGIS to decide if tile is still valid or not. That is, if the 
data for the requested area has changed. Depending on that finding...
4. GS answers "304 Not Modified" or gives GWC the freshly generated tile
5. GWC updates its cache and passes answer along (either "304 Not Modified" or 
new tile)

I've read about Caching with Last-Modified or E-Tag headers at 
http://geowebcache.org/docs/current/services/responseheaders.html#last-modified-and-if-modified-since
However, this only handles the communication between browser and GWC. How about 
the "backend communication" between GS and GWC?

Best,
Jens



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