django-lrucache-backend 4.0.0

About

lrucache_backend is an in-memory cache that has differing goals to the LocMemCache backend that Django provides.

Originally its purpose was to improve the cache eviction strategy, using an LRU algorithm over a random cull. However, Django 2.1 changed the LocMemCache to also use an LRU strategy.

Now, lrucache_backend has two major differences from Django.

1. Eliminates key char validation, improving performance at the cost of not being portable with memcache backends.

2. Eliminates serialization (pickling), allowing instances to be shared across requests. Any mutations performed on cache objects are maintained.

lrucache_backend functions as a global object cache, and uses a familiar Django interface to avoid poorly reimplementing local object caches in service layers:

def get_data_before(self):
    if not hasattr(self, '__data'):
        self.__data = self.expensive_query()
    return self.__data

def get_data_after(self):
    lcache = caches['local']
    data = lcache.get('our_data')
    if not data:
        data = self.expensive_query()
        lcache.set('our_data', data, timeout=600)
    return data

The benefits (despite the longer method) include timeouts, sharing data between requests, and avoiding network requests. This is especially useful when there are hundreds or thousands of property accesses that would hit the cache where network overhead would be prohibitive. The Fat model pattern can greatly benefit from tiered caching.

Installation

pip install django-lrucache-backend

Usage

Configure your CACHES Django setting appropriately:

CACHES = {
    'local': {
        'BACKEND': 'lrucache_backend.LRUObjectCache',
        'TIMEOUT': 600,
        'OPTIONS': {
            'MAX_ENTRIES': 100,
            'CULL_FREQUENCY: 100,
        },
        'NAME': 'optional-name'
    }
}

Note:

Set CULL_FREQUENCY == MAX_ENTRIES to only delete a single key per cull to only eliminate a single entry per cull. This maintains the LRU property most effectively, but can have performance implications.

And then use the cache as you would any other:

>>> from django.core.cache import caches

>>> local = caches['local']
>>> local.set('key', 123)
>>> local.get('key')
... 123

If you’re going to use this cache backend, then it’s highly recommended to use it as a non-default cache. That is, do not configure this cache under the default name.

Local memory caches compete for memory with your application so it’s in your best interests to use it as sparingly and deliberately as possible.

Compatibility

Django 2.2+ Python 3.6+

Licence

MIT

Authors

django-lrucache-backend was written by Josh Smeaton.