request doesn't fit into a rendering queue
RenderPrio, Render and RenderLow queues each only have a size of 32 entries. If these are full,
then requests overflow into the dirty queue. If this happens, renderd should send the NotDone
back immediately so that mod_tile doesn't wait for potentially a long time.
This however only worked for Render requests, but not RenderPrio or RenderLow. This patch fixes this.
* Only treat OPTIONS as preflight if Access-Control-Request-Method is set
* Only send Access-Control-Allow-Headers for preflight requests
* Don't send a bogus Access-Control-Allow-Headers value
In addition to Render and RenderPrio, add another priority level of RenderLow.
The idea is that if you rerender all tiles by touching planet-import-complete and
thereby likely overloading the server's rendering capacity you want to prioritize rerendering
of tiles that were explicitly marked dirty due to data changes over rerendering
due to planet-import-complete updates.
This is achieved by splitting rendering requests by if they are "old", or "very old".
As the tile expiry sets back the modification date many years, mod_tile splits
rendering requests based on how old the tiles are. If they are no more than a
certain threshold (currently set to one year) old, they are rendered with lower priority.
