I’ve spent the last few weeks playing around with django-page-cms. It’s going well so far. But I am having an issue with some customisations I made and the caching that is used. So here my notes so far on the subject. These are really for my own reference, but I thought others might find them helpful. The Django Project documentation describes the caching in detail as well.
Activating caching
You can turn on caching by using CACHE_BACKEND in the settings file.
Types of caching
There are five types of caching that come with Django:
1. Memcached
This uses the Memchached caching framework and is entirely memory based. Memcached can be downloaded from here: http://danga.com/memcached/. Memchached needs to be installed separately.
2. Database
This uses your database for caching. You need to create a table in your database using this command:
python manage.py createcachetable [cache_table_name]
and then use this setting:
CACHE_BACKEND = 'db://my_cache_table'
3. Filesystem chaching
This uses the file system for caching. You can set it up using the following setting:
CACHE_BACKEND = 'file:///var/tmp/django_cache'
Note: you need the three forward slashes after file and your webserver needs read/write access to the directory listed.
4. Local-memory caching
This provides the speed of memory caching if you don’t have the capability for running Memcached. It is multi-process and thread safe. However since each process therefore has it’s own chache, it is not bery memory efficient and best used in development environement only. Set it up like this:
CACHE_BACKEND = 'locmem:///'
5. Dummy caching
Used for development purposes to simulate caching, but without actually using a cache. Set it up like this:
CACHE_BACKEND = 'dummy:///'
You can also create your own custom chache mechanism if you wish.
CACHE_BACKEND arguments
There are three arguments:
- timeout: how long to chache the info for
- max_entries: maximum number of items to cache
- cull_percentage: what percentage to cull when max_entries is reached. eg: 3 means 1/3
Choosing what to cache
Caching a whole site
This can be done with middleware. See the docs for more info.
The per-view cach
This lets you cache the output of specific views. This is easy to setup:
@cache_page(60 * 15)
from django.views.decorators.cache import cache_page
def slashdot_this(request):
Template fragment caching
This lets you cache blocks within a template. You can do this using the following code:
{% load cache %}
{% cache 500 sidebar request.user.username %}
.. sidebar for logged in user ..
{% endcache %}{% load %} is the Django mechanism for loading custom tag libraries/
{% cache 500 sidebar request.user.username%} .. {% endcache %} defines the block to be cached. 500 is the length of the cache in seconds and any following items make up the key for the cache.
API caching
This lets you cache items programmatically. The core functions are:
cache.set('my_key', 'hello, world!', 30)
cache.get('my_key')
where my_key is the key for the item in the cache, ‘hello world!’ is the content being cached and 30 is the number of seconds to cache it for.
Further information on caching
You can also vary your cache depending on the request headers or use the cache_control decorator to control how private data is handled, whether to check for new versions and how many times a page can be chached.
