Missing support for rollback in django.core.cache

[Vlada Macek]

Tried unsuccessfully to find existing ticket for this, so starting an idea discussion.

In my project, I use memcached via django.core.cache to cache data resulting from some ORM operations. But when the database rolls back, the memcache is kept in the wrong state.

Currently I'm adding another layer with local dict (which has some speed improvements effects):

class DeferredMemcache(object):
    def __init__(self):
        from django.core import cache  # Importing this way so debug_toolbar can patch it later.

        self.real_cache = cache.cache
        self.local_cache = {}

    def get(self, key, default=None):
        try:
            value, deadline = self.local_cache[key]
        except KeyError:
            return self.real_cache.get(key, default)
        else:
            return value if deadline > time.time() else default

    def set(self, key, value, timeout):
        assert timeout > 0
        self.local_cache[key] = value, timeout + time.time()

    def commit(self):
        for key, (value, deadline) in self.local_cache.iteritems():
            timeout = deadline - time.time()
            if timeout >= 0:
                self.real_cache.set(key, value, timeout)

        self.local_cache.clear()

What do you think about adding some support for cache rollback in Django?

[Tim Graham]

Could you please open a discussion on the DevelopersMailingList to get feedback on the idea?

[Aymeric Augustin]

I believe this is a duplicate of #21803.