Try and make mapnik tiles more cache friendly
|Reported by:||amm||Owned by:||jburgess777@…|
Since the diff processing of mapnik tiles, the maximum cache age has reduced from the 7 days it used to be to something a lot lower.
Of cause, it isn't possible to predict the next time the tile changes, but one can try and create some heuristics that tries to be a compromise between cacheability and recency.
The current patch uses a system that is based on the tile dirtyness, the zoom level and the last modified time.
There are a bunch of constants defined in render_config to set the heuristic policy. The policy assumes, that low zoom tiles change less frequently noticably than higher level zooms, so they get cached longer.