Caching behaviour with default settings

[arneb]

Since the introduction of the CACHES setting Django by default uses the LocMemCache backend. Using multiple Django processes on the server, each process maintains it's own cache (as documented here: https://docs.djangoproject.com/en/1.6/topics/cache/#local-memory-caching).

I think this yields to outdated templates in the cache of all processes, except the one, that was used to save a change through the Django Admin.

Setting DBTEMPLATES_CACHE_BACKEND to None does not change the behaviour.

I think this behaviour needs to be documented, because I have to actively disable the LocMemCache setting to fix the problem with stale db-templates.

If I don't use caching at all in a project, I would normally not think about altering the Django default setting.

Environment: Django 1.6.2, Python 2.7.5, dbtemplates 1.3

Possibly related to #43

Edit: Using a DummyCache as the default cache fixed the problem with stale db-templates completely.

[jezdez]

Have you tried setting a LOCATION of the locmem backends as described in the Django settings?

[arneb]

No, because the point I wanted to make is: "If my project does not use Django's Cache Framework at all, I will never think about changing the CACHES setting and that will break dbtemplates".

If I make any use of Django caching in my project, I will definately use a cache backend thats works for my setup and then dbtemplates will of course work correctly.

The documentation says (https://github.com/jezdez/django-dbtemplates/blob/develop/docs/advanced.txt#L7):

To enable one of them you need to specify a setting called DBTEMPLATES_CACHE_BACKEND ...

And:

Starting in version 1.0 dbtemplates allows you also to set the new dict-based CACHES setting,
which was introduced in Django 1.3.
All you have to do is to provide a new entry in the CACHES dict named 'dbtemplates', e.g.:

What's missing is a clear indication that, If I do nothing, it will use CACHES['default'] and I have to make sure, that it's configured to work for my envirnoment.

After reading the documentation I thought that dbtemplates would only use the cache, if I activated it somehow. But it does it silently by default.
Then Django's default (LocMenCache) combined with my Process-based Django Workers lead to the strange behaviour of seeing outdated templates from some workers.

I opened the ticket because I think it might save others some time if this would be mentioned in the documentation.

[jezdez]

Ah, okay, thanks for the clarification, I'm sorry you had to find out that implicit behavior the hard way. This needs to be clarified indeed.

[mpasternak]

@arneb thank you for this problem report, would you mind submitting a pull request against the current docs?

[guettli]

Maybe this will be solved via PR #131