The idea is to implement namespaces using a decorator. This makes much more sense than having namespaces built-into the generic CacheProvider because namspaces only make sense for shared caches. So non-shared caches like ArrayCache should not have namespace logic at all.

Also the need to add namespaces depends on the usage. If a developer uses a global cache like Redis but does not reuse it it many unrelated places (where he cannot ensure cache ids do not collide), there is no point in adding namespaces. This also has the benefit to not add the overhead when not needed. The current overhead comes from reading the namespace version on each fetch. So currently each fetch does two accesses. The version is cached in the CacheProvider to boost the performance, but that can obivously result in race conditions. So this is removed in the decorator.

Decorating a cache with this namespace logic will also make sure that deleting all cache entries usingflushAll() will only remove the cache entries of the given namespace and not everything. This way one application/library can delete all of its cache without interfering with the shared cache of another app/library. This makesClearableCache::deleteAll obsolete. Classes that use a cache should not have to care aboutdeleteAll vsflushAll. They just want to delete the stuff. It's the task of the developer to make use of the namespace decorator when they have a global cache and different places where deletion can occur.

Todo

• Throw exception if decorated cache doesn't implement MultiGetCache or FlushableCache
• Add tests for decorator
• DeprecateCacheProvider::setNamespace andCacheProvider::getNamespace. In the next major version we can then remove namespacing from there and thus the cache providers that don't need it like ArrayCache will not by default inherit the namespace overhead.
• Updatehttps://github.com/doctrine/DoctrineCacheBundle to use NamespacedCacheDecorator when anamespace config is used
• Updatehttps://github.com/doctrine/doctrine2 to only useflushAll (ordeleteAll if we want to settle on this name). This is mainly used in cache clear commands.