caching

Caching

Basic

There are 3 tings, that will be cached.

1. Mapnik Style XML for each date
2. tile cache location
3. tile

The cache will be filled on each HTTP request, where there is no cached file or when using the prerendering command.

$ docker-compose -f local.yml run --rm django python manage.py prerender [ZOOM_LEVEL]

Below is a diagram, how the cache is used in a view.

Caching Objects

1. Mapnik Style XML for each date

Cache will be created, when a tile process is running. For each date, the system need a different mapnik style XML.

2. tile cache location

Cache location of a tile. To save space on the cache server, every tile will be hashed with MD5 and saved under the MD5 value. When multiple tiles have the same MD5 hash, then only one tile will be saved. The cache location key is year-month-day-zoom-X-Y.

3. tile

Finally, the tile PNG. The cache key is the hash value of the tile.

Config

In the config file, you can set, how low the cache should be saved.

# caching
# ------------------------------------------------------------------------------
# to which zoom level tiles should cached
ZOOM_LEVEL=13
# 2592000 == 1 month
TILE_CACHE_TIME=2592000

ZOOM_LEVEL to which zoom level the cache should be stored.

TILE_CACHE_TIME how long a tile should be cached in seconds.

Caching Objects

To clear up all cached files use

$ docker-compose -f local.yml run --rm django python manage.py clear_cache

But be careful, this command can't be undone!

Compression

To save space on the cache system, any cache object will be compressed with lzma. To change the compression mode, modify config/settings/production.py under CACHES. All available compression modes are listed here: https://docs.python.org/3/library/lzma.html#module-lzma