[OSM-dev] Ways on the new renderer... maybe usable after all!

[Lars Aronsson]

nick at hogweed.org wrote:

> While there is a slight slowdown, it's not too bad. For 
> instance, the renderer will render the way-rich tile with bbox 
> -0.75,51.02,-0.7,51.07 in 2.6 seconds if ways aren't fetched 
> from the database, against 3.7 if ways are fetched and rendered. 
> Other bboxes give similar time ratios, typically 3:4 no 
> ways:ways.

The 3:4 slowdown isn't too bad, but the times are too bad to begin 
with.  For a slippy map to work alright, tiles must perhaps be 
generated a hundred times faster: 26 and 37 milliseconds, rather 
than 2.6 and 3.7 seconds.  Today we draw roads only at zoom 11 and 
deeper, but it would be really nice to see roads at zoom 7.

Adding more hardware is not going to solve this.  We'd have to 
wait ten years for Moore's law to have that effect.  So how are we 
going to solve it?

Increasing the Squid timeout from 48 hours to 48 days might help. 
The over all experience would be faster panning and zooming, even 
if tile generation stays in the multiple second range.  But 
starting to draw roads at zoom 7 includes a SQL select of every 
little line segment in Greater London, and the occasional 
regeneration of any tile there could take minutes and hours.  
(Not to mention other drawbacks of longer Squid expiration.)


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se