Introduction

CacheMagic addresses the most common scenarios for caching and cache invalidation: temporal caching, instance caching, related objects caching, and thundering herd protection.

Temporal Caching

This is like memoizing an expensive operation. Usually something that doesn’t need to be super-fresh, and aggregates many objects - making invalidation difficult or impossible.:

@cached
def my_expensive_call(arg1, arg2):
    return do_other_things(arg1) * arg2

Instance Caching

This is the practice of caching individual model instances. CacheMagic provides a CacheController that you can attach to models to cause automatic caching and invalidations.

class Model(django.models.Model):
    cache = cachemagic.CacheController()
    field = django.models.TextField()

Model.objects.get(pk=27)    # hits the database
Model.cache.get(27)         # Tries cache first

Related Objects Caching

Having fetched an instance of a model, a frequent database operation is to find all the instances of another model that are related to your instance via foreign keys. You can attach a RelatedCacheController to your model to enable automatic caching and invalidation of these relations.

instance = Model.cache.get(pk=27)
related_things = instance.things_set.all()  # hits the database
related_things = instance.cache.things_set  # Tries cache first

The RelatedCacheController will automatically detect and cache objects related to the model it resides on by ForeignKeys, ManyToManyFields, and OneToOneFields.

Thundering Herd Protection

Any caching will be useless when a cache key expires and thousands of requests try to recompute the value at the same time. CacheMagic provides a cache backend for redis that prevents this problem by designating only one client to recompute the value while others simply read the existing cache value.

CACHES['default'] = {
    'BACKEND': 'cachemagic.cache.RedisHerdCache',
    'LOCATION': ':'.join([REDIS_HOST, str(REDIS_PORT), '0']),
    'OPTIONS': {
        'PASSWORD': REDIS_PASSWORD,
    },
}