Site-Wide Caching in Django
My last article about caching RSS feeds in a Django project generated a lot of interest. My original goal was to help other people who have tried to cache QuerySet objects and received a funky error message. Many of my visitors offered helpful advice in the comments, making it clear that I was going about caching my feeds the wrong way.
I knew my solution was wrong before I even produced it, but I couldn't get Django's site-wide caching middleware to work in my production environment. Site-wide caching worked wonderfully in my development environment, and I tried all sorts of things to make it work in my production setup. It wasn't until one "Jacob" offered a beautiful pearl of wisdom that things started to make more sense:
How To Setup Site-Wide Caching
While most of this can be gleaned from the official documentation, I will repeat it here in an effort to provide a complete "HOWTO". For further information, hit up the official caching documentation.
The first step is to choose a caching backend for your project. Built-in options include:
- database (cached objects are stored in your database)
- local memory
To specify which backend you want to use, define the CACHE_BACKEND variable in your settings.py. The definition for each backend is different, so check out the official documentation for details.
Next, install a couple of middleware classes, and pay attention to where the classes are supposed to appear in the list:
- django.middleware.cache.UpdateCacheMiddleware - This should be the first middleware class in your MIDDLEWARE_CLASSES tuple in your settings.py.
- django.middleware.cache.FetchFromCacheMiddleware - This should be the last middleware class in your MIDDLEWARE_CLASSES tuple in your settings.py.
Finally, you must define the following variables in your settings.py file:
- CACHE_MIDDLEWARE_SECONDS - The number of seconds each page should be cached
- CACHE_MIDDLEWARE_KEY_PREFIX - If the cache is shared across multiple sites using the same Django installation, set this to the name of the site, or some other string that is unique to this Django instance, to prevent key collisions. Use an empty string if you don't care
If you don't use anything like Google Analytics that sets/changes cookies on each request to your site, you should have site-wide caching enabled now. If you only want pages to be cached for users who are not logged in, you may add CACHE_MIDDLEWARE_ANONYMOUS_ONLY = True to your settings.py file--its meaning should be fairly obvious.
If, however, your site-wide caching doesn't appear to work (as it didn't for me for a long time), you can create a special middleware class to strip those dirty cookies from the request, so the caching middleware can do its work.
import re class StripCookieMiddleware(object): """Ganked from http://2ze.us/Io""" STRIP_RE = re.compile(r'\b(_[^=]+=.+?(?:; |$))') def process_request(self, request): cookie = self.STRIP_RE.sub('', request.META.get('HTTP_COOKIE', '')) request.META['HTTP_COOKIE'] = cookie
Edit: Thanks to Tal for regex the suggestion!
Once you do that, you need only install the new middleware class. Be sure to install it somewhere between the UpdateCacheMiddleware and FetchFromCacheMiddleware classes, not first or last in the tuple. When all of that is done, your site-wide caching should really work! That is, of course, unless your offending cookies are not found by that STRIP_RE regular expression.
Thanks again to Jacob and "nf", the original author of the middleware class I used to solve all of my problems! Also, I'd like to thank "JaredKuolt" for the django-staticgenerator on his github account. It made me happy for a while as I was working toward real site-wide caching.