tilestache: use memcache instead of disk for tile storage

So far, tiles have been stored on disk which, in combination with
bad disk performance, made the map slow and laggy.

This patch switches to memcache, which will remove the dependency
on disk performance for loading cached tiles entirely.

Note that installing and configuring memcached will be required
manually like for the other dependencies.

Signed-off-by: Fabian Bläse <fabian@blaese.de>
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

README.md

@@ -8,7 +8,7 @@
 
 ## Debian Dependencies
 ```bash
-apt-get install mysql-server python3-mysqldb python python3 python3-requests python3-lxml python3-pip python3-flask python3-dateutil python3-numpy python3-scipy python3-mapnik python3-pip uwsgi-plugin-python3 nginx
+apt-get install mysql-server memcached python3-memcache python3-mysqldb python python3 python3-requests python3-lxml python3-pip python3-flask python3-dateutil python3-numpy python3-scipy python3-mapnik python3-pip uwsgi-plugin-python3 nginx
 pip3 install wheel pymongo pillow modestmaps simplejson werkzeug
 ```
 

ffmap/mapnik/tilestache.cfg

@@ -1,7 +1,6 @@
 {
 	"cache": {
-		"name": "Disk",
-		"path": "/var/cache/ffmap/tiles/"
+		"name": "Memcache"
 	},
 	"layers": {
 		"tiles/routers": {

install.sh

@@ -13,9 +13,6 @@ cp -v ffmap/mapnik/tilestache.cfg /usr/share/ffmap
 cp -rv ffmap/web/static /usr/share/ffmap
 cp -rv ffmap/web/templates /usr/share/ffmap
 
-mkdir -vp /var/cache/ffmap/tiles/
-chown -R www-data:www-data /var/cache/ffmap/tiles/
-
 cp -v ffmap/systemd/*.service /etc/systemd/system/
 systemctl daemon-reload