[OSM-dev] Improvement of tile rendering

[Udo Giacomozzi]

Hello Jon,

Friday, March 20, 2009, 7:48:42 PM, you wrote:
JB> If you want to mess around with a slightly higher level implementation,
JB> I recently re-implemented the mod_tile render daemon into python [1].

Unfortunately I'm not familiar with Python.


JB> It is functionally equivalent to the C render daemon.

BTW, where can I find the source code of the C daemon?


JB> It still requires the
JB> C mod_tile module, but I am considering writing a python version of that
JB> too.


You might want to use FastCGI instead of messing around with Apache
modules. It offers a number of advantages:

- in this case a Apache module is probably not really faster than a
  FastCGI implementation

- FastCGI would allow you to keep rendering daemon and request
  handling at one place (in one process)

- FastCGI is more portable, as it is not bound to Apache (consider
  Lighttpd)

- you have full control over threading, like limiting the number of
  concurrent requests. This is very important for optimizazion.

- your FastCGI server can be restarted/replaced or crash at any time
  without bringing the whole web server down

- the FastCGI server runs with it's own system user, which makes file
  access (caching...) easier

I'm using FastCGI in a number of projects and programming languages.
Some of them easily handle up to 100 requests per second on a standard
server.


JB> The purpose of these is to allow easier experimentation. If some good
JB> new ideas develop then I may adopt them into the C code. Another
JB> possibility is mixing the two implementations together by linking an
JB> embedded python interpretor into the C code.

...I'm sure Python supports FastCGI. If you are unfamiliar with it,
you should have a look at it. It's very simple (which makes it so
good).


Anyway, I would suggest to do any dynamic processing only in case a
tile is missing (i.e. installing it as a error 404 handler), because
most requests will probably go to already rended tiles. In this case
the web server will just have to serve a static file without having to
invoke Python or anything.

Udo