Right now it's possible to use the same memcached instance with moodle for both php sessions and muc store.

memcached implementation has a well-known (MDL-45375) inability to invalidate/purge group of keys, so current implementation simply deletes everything on purge of any cache.

That can hit php sessions being deleted together with MUC contents, and that can lead to real problems, invalidating moodle sessions in the middle (of a quiz, of a post...).

So it would be great to articulate some way to detect if the same memcached instance is being used for both php sessions and muc and warn, loud and in red about the risks of such combination.

Perhaps with a "fixed" key, or comparing settings or whatever. And to be shown in the admin notifications or in environment info or wherever.

Anything visible enough. Ciao