[OSM-dev] rendering: mad ideas

Mikel Maron mikel_maron at yahoo.com
Sat Mar 25 13:14:32 GMT 2006


I don't recall the problems precisely, I'd need to get re-embedded in squid and tiling.

only-if-cached looks like useful stuff potentially.

Remember the subject of this thread is "mad ideas"! mad ideas are good (what else could you call mapping the entire world with gps units ;), but I think there are some saner ideas to start with first. Getting some intelligent cache invalidation working is probably the next best step. And continuing to refine speed up rendering on the server -- in C or even perl rather than Ruby. I've unfortunately had to focus on other things recently, maybe there'll be time upcoming, or maybe somone else would like to look at this in detail.

----- Original Message ----
From: Erik Johansson <erjohan at gmail.com>
To: Dev Openstreetmap <dev at openstreetmap.org>
Sent: Friday, March 24, 2006 1:23:47 PM
Subject: Re: [OSM-dev] rendering: mad ideas

On 3/24/06, Mikel Maron <mikel_maron at yahoo.com> wrote:
> The last time I was investigating this, things got stuck with Squid. I was trying to implement cache invalidation on a list of cache objects, using the squidpurge tool, and it wasn't working brilliantly. Help welcome.

What was the problem? I have to date had no problem with invalidating
my very very very simple test pages (just ordinary CGIs without
changing the URLs)..

I got a nice tip from Henrik Nordström of Squid fame, if you add a
header to the request  you can tell squid to only give to the image if
it is cached. Very usefull, and perhaps a good idea to use in the
applet..

Cache-Control: only-if-cached

Compare:
# noncached tile
wget --header "Cache-Control: only-if-cached"
'http://tile.openstreetmap.org/cgi-bin/steve/mapserv?map=/usr/lib/cgi-bin/steve/wms.map&service=WMS&WMTVER=1.0.0&REQUEST=map&STYLES=&TRANSPARENT=TRUE&LAYERS=landsat,streets&WIDTH=256&HEIGHT=128&BBOX=17.841873,59.332920536311434,17.929764,59.39'

# cached tile
wget http://tile.openstreetmap.org/cgi-bin/steve/mapserv?map=/usr/lib/cgi-bin/steve/wms.map&service=WMS&WMTVER=1.0.0&REQUEST=map&STYLES=&TRANSPARENT=TRUE&LAYERS=landsat,streets&WIDTH=256&HEIGHT=128&BBOX=17.841873,59.332920536311434,17.929764,59.355327237805916

--
/Erik

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