Thanks for this explanation. I'm not sure to understand why you don't support last-modified.
I understand that ETag allows to handle new tile with same content. But it is more complex as it need to store metadata for the tile. With last-modified solution, we simply have to send the timestamp of the file (a metadata already stored by any filesystem). Of course, we don't avoid new file with same content, but I expect we can avoid some downloads in many case. Is it possible to imagine both system: - last-modified for simple client - Etag for evolved client 2010/2/17 Jon Burgess <jburgess...@googlemail.com>: > On Wed, 2010-02-17 at 21:43 +0100, Jocelyn Jaubert wrote: >> Hi Guilhem, >> >> Le 16 février 2010, Guilhem Bonnefille a écrit : >> > 2010/2/7 Greg Troxel <g...@ir.bbn.com>: >> > > I don't see how to set the new 'tiles fresh enough' paramater. It >> > > seems OSM mapnik updates from minutely tiles; it's cool to grab >> > > them when you want, but a lot of server load normally. I suggest a >> > > week for the default fresh-enough-not-to-ask time, but I don't see >> > > how to set that in the GUI and I don't see it in the viking file. >> > >> > I added a preference for setting this value dynamically. Check Git >> > repo at SourceForge. >> > >> > But I fear that this feature is no more functional: I did many tests >> > and I feel tiles are always downloaded (from tile.openstreetmap.org). >> > Jocelyn, as you are the author of this feature, can you give it a try? >> >> I have looked at what is sent to the server, and received from it (via >> the -V switch) and it seems that tile.openstreetmap.org returns a tile >> even if it was not updated on the server. >> >> But if you try on the OSM server, then it works correctly: no tile is >> sent by the server if viking already has a recent tile. > > Do you mean that the osmarender server works as you expect here? > > > I wrote the mod_tile code which serves the tiles from > tile.openstreetmap.org and can give you some background on the current > behaviour. We made a decision to make use of the ETag header instead of > the last-modified field. Tiles often get re-rendered without the > contents changing. If we used the last-modified time then this would > result in the tile being downloaded unnecessarily. > > Instead, we return an ETag header in the HTTP response for each tile > which is derived from the md5sum of the tile. If the tile gets > re-rendered and the content is identical to the previous tile then the > ETag should match even if the last-modified-time was updated. > > > When the client makes a request it should store the ETag returned. When > it comes to request the tile again the client includes this ETag in a > If-None-Match header. If the current tile on the server still has the > same content then this will trigger a 304/NotModified response. I have > included an example of in an attachment. > > We also return "Expires:" and "Cache-Control:" headers which can assist > the client in deciding when to try requesting the tile again. > > All these headers are defined in the various HTTP RFCs. In theory, > properly written web browsers and caches should work fine with them but > I am beginning to wonder whether I should discard the ETag and move back > to a simple last-modified time system. > > Jon > > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Viking-devel mailing list > Viking-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/viking-devel > Viking home page: http://viking.sf.net/ > -- Guilhem BONNEFILLE -=- JID: gu...@im.apinc.org MSN: guilhem_bonnefi...@hotmail.com -=- mailto:guilhem.bonnefi...@gmail.com -=- http://nathguil.free.fr/ ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
