[OSM-dev] Renderd problems.

Jochen Topf jochen at remote.org
Sat Oct 2 14:48:25 BST 2010

On Sat, Oct 02, 2010 at 01:28:48PM +0100, Kai Krueger wrote:
> On -10/01/37 20:59, Peter Körner wrote:
>> but renderd had a hard limit of 1000 tiles in the queue.
> For completeness sake, I thought I'd mention that you can change that  
> limit quite easily. Simply change the constant at  
> http://trac.openstreetmap.org/browser/applications/utils/mod_tile/render_config.h#L73 
> to a higher value and you should be done (well OK, the constant the line  
> below also should be adjusted).
> That limit used to be there, I think, as the queue used a linear list,  
> which meant adding and searching tiles where O(n), thus n was limited.  
> It now uses a hashtable lookup, so that limit could be much higher  
> without problems.
> On the main OSM tile server, I believe, that limit is still there as a  
> feature rather than a bug. In order to achieve a fast turn around time  
> for mappers, the queue is limited, thus also "limiting" the time a  
> request takes to get through the queue. Instead requests are dropped  
> completely and the next time someone views the tile, mod_tile again  
> tries to queue it. This has the advantage that frequently viewed tiles  
> are more likely to end up in the queue and then are quickly rendered.
> Ideally, you would probably have a large priority queue with the  
> priority boosted every time another request comes in for that tile. But  
> that isn't implemented. Does tirex support that?

No, its doesn't. But you could add something like this externally. Have
a process read the log file and count requests and re-queue them with
rising priority and possibly the "only-if-older-than-filter".

It also supports an expire time for queued requests. So you can queue a
metatile and give the request an expire time. If the metatile couldn't be
rendered in time, it will silently drop out of the queue. If a new request
for the same metatile comes in, the expire timer starts anew.

Jochen Topf  jochen at remote.org  http://www.remote.org/jochen/  +49-721-388298

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