Invalidation of multiple caches efficiently in Django

Question

In my project I own the following model:

class Item(models.Model):
    month = models.DateField('month', null=False, blank=False, db_index=True)
    kg = models.BigIntegerField('kg')
    tags = models.ManyToManyField('Tag', related_name='items')
    // vários outros campos utilizados para filtrar

And I have the report_view which returns the sum of kg by Month and by tag in accordance with os filtros provided in the query of URL.

That one view returns something like this:

--------------------------------
|Tag    |jan    |fev    |mar   |
--------------------------------
|Tag 1  |1000   |1500   |2000  |
--------------------------------
|Tag 2  |1235   |4652   |0     |
--------------------------------

Like my table Item already has more than 4 million records and is always growing, my report_view always stays in the cache.

So far so good.

The problem is: users of the site can change the tags of Items and whenever this occurs it is necessary to invalidate the caches, but I’d like to do it in a more granulated.

For example, if a user changes the tag in a Item of janeiro this should only invalidate the caches of janeiro (I prefer that the caches are by month than by tag for sometimes a tag interferes with the other). But I don’t know what all the views who went to cache because there are thousands of possibilities of different filters that change the URL.

What I’ve managed to do so far:

• Create a signal which invalidates all caches whenever a tag mute

@receiver(m2m_changed, sender=Item.tags.through)
def tags_changed(sender, **kwargs):
    cache.clear()

But it clears all which is not good..

There is a way to mark caches so something like this can be done:

cache.filter('jan').clear()