[OSM-dev] Mapnik's speed rendering slow ?

[Shaun McDonald]

On 8 Nov 2008, at 17:22, sylvain letuffe wrote:

>> 0.5s per tile looks about right. The main tile server does not manage
>> to render all z18 tiles in 24 hours.
> Glups then...
>
> (...)
>> http://wiki.openstreetmap.org/index.php/Mod_tile
>
> Thanks all for the link, I already had a look at mod_tile and I  
> first thought
> it wouldn't fit my needs and then be a second choice.
>
> I'm willing to (did I say dreaming ?)
> 1) have a max older tile of 24h
> 2) don't kill my server under load
> 3) have a fast responsive Openlayer (which I have with all tiles  
> generated)
>
> mod_tile seams to me not beeing able to cover 3 (unless someone got  
> the pain
> to explore the same place before you, or unless we drop under ~0.02s  
> per
> tiles, in wich case I'll stop bothering with caching tiles and have  
> them
> rendered real-time )

At a recent trade show where OpenStreetMap was showcased, we had  
mod_tile running on a dual core laptop with the UK extract rendering  
the data live. It all seemed to work, though once in a while a refresh  
was required of the slippy map.

>
>
> 2->, as of the readme, is not completly sure, unless some users are  
> kicked
> off. because If simultaneously, 20 users are exploring a "new" region
> somewhere in mountain, the 0.5s/tile will soon transforms into much  
> higher,
> transforming mapnik into unusable
>
> Sounds like a corner case right ?
>

On a fast enough server that won't be a problem.

> So, staying for now with my idea, is there some mecanism implemented  
> (or to be
> implemented) in mapnik to :
> - When a tile is empty, not try to generate it (use a defined png  
> model
> instead), and not try to generate any other tiles included in zoom  
> greater
> than it
> - On each postgres "osm data update" ( with some kind of last- 
> modified flag ?)
> use them to render only last modified zones, wich, to my point of  
> vew seams
> to be much less numerous that vews

There is already a script in svn for doing tile expiry of the updates  
when using modtile.

http://www.asklater.com/matt/wordpress/?p=80

Shaun


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