1. Run ``pip install django-redis-cache``.
2. Modify your Django settings to use ``redis_cache``.
.. code:: python
When using TCP connections
CACHES = {
'default': {
'BACKEND': 'redis_cache.RedisCache',
'LOCATION': [
'<host>:<port>',
'<host>:<port>',
'<host>:<port>',
],
'OPTIONS': {
'DB': 1,
'PASSWORD': 'yadayada',
'PARSER_CLASS': 'redis.connection.HiredisParser',
'CONNECTION_POOL_CLASS': 'redis.BlockingConnectionPool',
'CONNECTION_POOL_CLASS_KWARGS': {
'max_connections': 50,
'timeout': 20,
},
'MAX_CONNECTIONS': 1000,
'PICKLE_VERSION': -1,
},
},
}
When using unix domain sockets
Note: ``LOCATION`` needs to be the same as the ``unixsocket`` setting
in your redis.conf
CACHES = {
'default': {
'BACKEND': 'redis_cache.RedisCache',
'LOCATION': '/path/to/socket/file',
'OPTIONS': {
'DB': 1,
'PASSWORD': 'yadayada',
'PARSER_CLASS': 'redis.connection.HiredisParser',
'PICKLE_VERSION': 2,
},
},
}
For Master-Slave Setup, specify the host:port of the master
redis-server instance.
CACHES = {
'default': {
'BACKEND': 'redis_cache.RedisCache',
'LOCATION': [
'<host>:<port>',
'<host>:<port>',
'<host>:<port>',
],
'OPTIONS': {
'DB': 1,
'PASSWORD': 'yadayada',
'PARSER_CLASS': 'redis.connection.HiredisParser',
'PICKLE_VERSION': 2,
'MASTER_CACHE': '<master host>:<master port>',
},
},
}
Usage
=====
django-redis-cache shares the same API as django's built-in cache backends,
with a few exceptions.
``cache.delete_pattern``
Delete keys using glob-style pattern.
example::
>>> from news.models import Story
>>>
>>> most_viewed = Story.objects.most_viewed()
>>> highest_rated = Story.objects.highest_rated()
>>> cache.set('news.stories.most_viewed', most_viewed)
>>> cache.set('news.stories.highest_rated', highest_rated)
>>> data = cache.get_many(['news.stories.highest_rated', 'news.stories.most_viewed'])
>>> len(data)
2
>>> cache.delete_pattern('news.stores.*')
>>> data = cache.get_many(['news.stories.highest_rated', 'news.stories.most_viewed'])
>>> len(data)
0
``cache.clear``
Same as django's ``cache.clear``, except that you can optionally specify a
version and all keys with that version will be deleted. If no version is
provided, all keys are flushed from the cache.
``cache.reinsert_keys``
This helper method retrieves all keys and inserts them back into the cache. This
is useful when changing the pickle protocol number of all the cache entries.
As of django-redis-cache < 1.0, all cache entries were pickled using version 0.
To reduce the memory footprint of the redis-server, simply run this method to
upgrade cache entries to the latest protocol.
Thundering Herd Protection
==========================
A common problem with caching is that you can sometimes get into a situation
where you have a value that takes a long time to compute or retrieve, but have
clients accessing it a lot. For example, if you wanted to retrieve the latest
tweets from the twitter api, you probably want to cache the response for a number
of minutes so you don't exceed your rate limit. However, when the cache entry
expires you can have mulitple clients that see there is no entry and try to
simultaneously fetch the latest results from the api.
The way to get around this problem you pass in a callable and timeout to
``get_or_set``, which will check the cache to see if you need to compute the
value. If it does, then the cache sets a placeholder that tells future clients
to serve data from the stale cache until the new value is created.
Example::
tweets = cache.get_or_set('tweets', twitter.get_newest, timeout=300)
Running Tests
=============
``./install_redis.sh``
``make test``
.. _redis-py: http://github.com/andymccurdy/redis-py/
.. _redis: http://github.com/antirez/redis/
.. _hiredis: http://github.com/antirez/hiredis/
.. _python: http://python.org