This one is available since APCu 4.0, since we require APCu 4.0.6 this works fine. Also it brings us PHP 7 compatibility and thus fixes https://github.com/owncloud/core/issues/21095

For enhanced security it is recommended to configure Redis to only accept connections with a password. (http://redis.io/topics/security)

This is especially critical since Redis supports the LUA scripting language and thus a simple SSRF vulnerability (as proven in http://benmmurphy.github.io/blog/2015/06/04/redis-eval-lua-sandbox-escape/ for example) may lead to a remote code execution.

Newer Memcached's do not support the underlying protocol commands that
getAllKeys() is implemented with. We should fallback to clearing
everything in that case, as causing (temporary) performance problems for
other applications on the server is better than having stale cached data.

Warning is now printed to logs, but occ and cron will still work.

Instead of falling back to null memcache, throw exceptions.
Also throw file locking specific exceptions in case the class is not
available.

This reverts commit ff24554e.

This prevents breaking ownCloud completely when memcache is not enabled
and the locking code is triggered

Prevents to have the cache reused by other instances on the server which have possible the same instance ID and also invalidates older cache entries after an upgrade which can cause unwanted side-effects.

Impact for deployment: The same cache will only get used if ownCloud is installed with the same version and under the same path. But this should be a basic requirement anyways.

Caches divided up into two groups: distributed and local. 'Low latency' is an
alias for local caches, while the standard `create()` call tries to get
distributed caches first, then local caches.

Memcache backend is set in `config.php`, with the keys `memcache.local` and
`memcache.distributed`. If not set, `memcache.distributed` defaults to the value
of `memcache.local`.

This reverts commit 6a1a4880.

APCu before 4.0.6 is unbelievable buggy and tend to segfault the PHP process (i.e. the whole webserver)

This potentially fixes https://github.com/owncloud/core/issues/14175

Requires a backport to stable8