Cached pages can crash on 3.1 to 3.2 upgrade

[Iuri de Silvio]

My cached page from 3.1 crashes because I have a middleware setting a header.

Because cache_page do a pickle caching, we have a 3.1 JsonResponse running on 3.2, without the new headers feature.

AttributeError: 'JsonResponse' object has no attribute 'headers'
  File "django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "commons/middleware.py", line 44, in __call__
    response['X-Current-Version'] = VERSION
  File "django/http/response.py", line 172, in __setitem__
    self.headers[header] = value

Docs could provide some help about this, the fix should be easy cleaning specific cache or using CACHE_MIDDLEWARE_KEY_PREFIX. that is unfortunately broken.

https://code.djangoproject.com/ticket/32841

[Carlton Gibson]

Hi.

...we have a 3.1 JsonResponse running on 3.2...

I can't see how that's ever going to be supported. The response API doesn't change often but if it does you'll have to clear the cache. You note this:

...fix should be easy cleaning specific cache...

This seems a bit particular to merit specific documentation.

[Simon Charette]

FWIW we've used the KEY_FUNCTION ​setting to namespace keys of CACHES entries doing rich object serde by Django major version to prevent these issues from happening. You have to be careful to do a progressive rollout to prevent cache miss stampedes but it completely avoids these kinds of issues.

[Iuri de Silvio]

I didn't knew about this KEY_FUNCTION.

It would be a problem in my case because we have other keys in the same cache, but not difficult to move to a different cache and use that.

Thanks!