django-ultracache 1.9.0

Installation

1. Install or add django-ultracache to your Python path.

2. Add ultracache to your INSTALLED_APPS setting.

3. Ensure django.core.context_processors.request is in TEMPLATE_CONTEXT_PROCESSORS setting.

Usage

django-ultracache provides a template tag {% ultracache %} that functions like Django’s standard cache template tag, with these exceptions.

1. It takes the sites framework into consideration, allowing different caching per site.

2. It allows undefined variables to be passed as arguments, thus simplifying the template.

3. Crucially, it is aware of model objects that are subjected to its caching. When an object is modified all affected cache key are automatically expired. This allows the user to set longer expiry times without having to worry about stale content.

4. The cache invalidation can be extended to issue purge commands to Varnish, Nginx or other reverse caching proxies.

Simplest use case:

{% load ultracache_tags %}
{% ultracache 3600 'my_identifier' object 123 undefined 'string' %}
    {{ object.title }}
{% endultracache %}

The tag can be nested. ultracache is aware of all model objects that are subjected to its caching. In this example cache keys outer and inner_one are expired when object one is changed but cache key inner_two remains unaffected:

{% load ultracache_tags %}
{% ultracache 1200 'outer' %}
    {% ultracache 1200 'inner_one' %}
        title = {{ one.title }}
    {% endultracache %}
    {% ultracache 1200 'inner_two' %}
        title = {{ two.title }}
    {% endultracache %}
{% endultracache %}

django-ultracache also provides a decorator cached_get to cache your views. The parameters follow the same rules as the ultracache template tag except they must all resolve. request.get_full_path() is always implicitly added to the cache key:

from ultracache.decorators import cached_get


class CachedView(TemplateView):
    template_name = "ultracache/cached_view.html"

    @cached_get(300, "request.is_secure()", 456)
    def get(self, *args, **kwargs):
        return super(CachedView, self).get(*args, **kwargs)

The cached_get decorator can be used in an URL pattern:

from ultracache.decorators import cached_get

url(
    r"^cached-view/$",
    cached_get(3600)(TemplateView.as_view(
        template_name="myproduct/template.html"
    )),
    name="cached-view"
)

Do not indiscriminately use the cached_get decorator. It only ever operates on GET requests but cannot know if the code being wrapped retrieves data from eg. the session. In such a case it will cache things it is not supposed to cache.

If your view is used by more than one URL pattern then it is highly recommended to apply the cached_get decorator in the URL pattern. Applying it at class level may lead to cache collisions, especially if get_template_names is overridden.

You can create custom reverse caching proxy purgers. See purgers.py for examples:

ULTRACACHE = {
    'purge': {'method': 'myproduct.purgers.squid'}
}

Automatic invalidation defaults to true. To disable automatic invalidation set:

ULTRACACHE = {
    'invalidate': False
}

django-ultracache maintains a registry in Django’s caching backend (see How does it work). This registry can’t be allowed to grow unchecked, thus a limit is imposed on the registry size. It would be inefficient to impose a size limit on the entire registry so a maximum size is set per cached value. It defaults to 25000 bytes:

ULTRACACHE = {
    'max-registry-value-size': 10000
}

It is highly recommended to use a backend that supports compression because a larger size improves cache coherency.

How does it work?

django-ultracache monkey patches django.template.base.Variable._resolve_lookup to make a record of model objects as they are resolved. The ultracache template tag inspects the list of objects contained within it and keeps a registry in Django’s caching backend. A post_save signal handler monitors objects for changes and expires the appropriate cache keys.

Tips

1. If you arre running a cluster of Django nodes then ensure that they use a shared caching backend.

2. Expose objects in your templates. Instead of passing object_title to a template rather have the template dereference object.title.

1.9.0

1. Move to tox for tests.

2. Django 1.9 compatibility.

0.3.8

1. Honor the raw parameter send along by loaddata. It prevents redundant post_save handling.

0.3.7

1. Revert the adding of the template name. It introduces a performance penalty in a WSGI environment.

2. Further reduce the number of writes to the cache.

0.3.6

1. Add template name (if possible) to the caching key.

2. Reduce number of calls to set_many.

0.3.5

1. Keep the metadata cache size in check to prevent possibly infinite growth.

0.3.4

1. Prevent redundant sets.

2. Work around an apparent Python bug related to di[k].append(v) vs di[k] = di[k] + [v]. The latter is safe.

0.3.3

1. Handle case where one cached view renders another cached view inside it, thus potentially sharing the same cache key.

0.3.2

1. The ultracache template tag now only caches HEAD and GET requests.

0.3.1

1. Trivial release to work around Pypi errors of the day.

0.3

1. Replace cache.get in for loop with cache.get_many.

0.2

1. Do not automatically add request.get_full_path() if any of request.get_full_path(), request.path or request.path_info is an argument for cached_get.

0.1.6

1. Also cache response headers.

0.1.5

1. Explicitly check for GET and HEAD request method and cache only those requests.

0.1.4

1. Rewrite decorator to be function based instead of class based so it is easier to use in urls.py.

0.1.3

1. cached_get decorator now does not cache if request contains messages.

0.1.2

1. Fix HTTPResponse caching bug.

0.1.1

1. Handle case where a view returns an HTTPResponse object.

0.1

1. Initial release.