Hi.
Looking at the render queue on ptolemy, I often observe metatiles for powermap Z9 or Z10 timing out. Powermap is not the only one, bw-mapnik and bw-noicons is another candidate, too, for other Zoom levels.
Then what happens, the metatile is not rendered, and when the browser user zooms in and out, the same long rendering resulting in a timeout happens again. (To me it seems that much of Z9/Z10 for the powermap just cannot be rendered in germany, but admittedly that's a guess.)
So this is bad in two ways: first, the queue is congested with long running tasks, second, this happens over and over again. While the first thing cannot easily be changed, the second, worse, point could be avoided:
Why not just put a (mostly transparent) metatile saying "timeout" as the rendering result? So for the style creator it would easily be trackable what zoom level (or detail) is problematic, and for the user it would be possible to just issue a manual "/dirty", if the user thinks it may be worthwhile to try rendering again.
Kind regards, Kay