Cached objects become stale after Django upgrade

[elgintg]

After upgrading Django version to 4.2 few months back, I now notice warning messages:

RuntimeWarning: Pickled model instance's Django version 3.2.14 does not match the current version 4.2.16.

These come from pickled switch objects in Redis cache. After having deleted all waffle keys from Redis, warnings are now silenced. By reading docs and going through the source code, I couldn't find any management command for clearing cache. I think the ideal solution would be to add new setting for cache expiration time.

In my particular case, I use only switches and hitting database from time to time for refreshing entries is totally fine.

[dancergraham]

Hello, thank you for reporting this.

I think this is covered by the Django upgrade guidelines here: https://docs.djangoproject.com/en/5.1/howto/upgrade-version/#deployment

It recommends clearing the cache on upgrade for this reason - Django provides a method for this (but not a management command). This stack overflow post discusses options: https://stackoverflow.com/questions/5942759/best-place-to-clear-cache-when-restarting-django-server