[OSM-dev] Creating Easy Map Embedding

[David Earl]

On 22/10/2007 15:42, Christopher Schmidt wrote:
> On Mon, Oct 22, 2007 at 03:01:46PM +0100, David Earl wrote:
>> Why don't we create a distributed tile server, so the load can be spread 
>> around? Then we do have "infinite resources like Google".
> 
> Building a distributed tile server is a lot of work, and not easy. (I
> say this having built the innards of a distributed tile cache for
> TileCache.)
> 
> How many people have the ability to set up and maintain an up to date
> copy of the mapnik database? How many people have the server resources to
> deploy mapnik, PostGIS, etc. as well as maintaining an up to date copy
> of the planet that doesn't fall behind? 

I wasn't anticipating the rendering would be distributed, just the tile 
serving. I think the present algorithm for re-rendering is wasteful - it 
is too late because the request is made after someone has tried to look 
at a tile. I think it needs to be done in response to changes in the data.

If lots of people start wanting tiles, then that will outweigh 
re-rendering based on change rather than demand.

> I think that if you browse
> informationfreeway, which uses distributed caches of tiles, you'll see
> the benefit this has, but also the drawback, which is that you're
> depending on your tile caches to always be available -- when they
> aren't, the whole map suffers.


Well, most of the time now the centralised server fails to deliver at 
least one tile on most occasions I look at it. There are many times when 
I fail to get a response at all and just an array of pink tiles.


> A distributed tile cache is a difficult problem to solve, and it's not
> the most important part of the problem here: 


Only because of the algorithm, that says render tiles after someone has 
attempted to look at them (and who will therefore not see them).


> The more important question -- at least to me -- is "What resources does
> OSM want to be providing to users of OSM?" Is 'tiles' one of them, or is
> the OSM tile server only a resource designed to be used for OSM.org, and
> everything else belongs off site? I don't know how others feel about
> this question, and I'd be interested in hearing what others think.


The easier it is to incorporate, the more people are likely to make use 
of OSM.


> A distributed tile cache is a difficult problem to solve

Tiles at home was a difficult problem to solve, but it was done.

But it doesn't seem an insurmountable problem.

In any case a single central server will have have to distribute 
resources sooner or later if demand outstrips the capabilities of one 
server, though it may be somewhat easier when it is all under central 
control.

David