Merge pull request #12134 from nextcloud/docs/apcu

docs(admin): Add more details about configuring APCu

admin_manual/configuration_server/caching_configuration.rst

@@ -121,6 +121,24 @@ Refresh your Nextcloud admin page, and the cache warning should disappear.
    config file or append ``--define apc.enable_cli=1`` to the cron job call.
 
 
+Depending on your installation size and the number of users and interactions
+with the system you may want to adapt the ``apc.shm_size`` setting in your
+``php.ini``. The default value is 32M which is usually too low for Nextcloud. A
+good starting point is 128M. If you have a lot of users and/or a lot of apps
+installed you may want to increase this value further. Keep in mind that this
+memory needs to be available in your system's memory and kept in mind when
+sizing the amount of workers on your server.
+
+A frequenly resetting cache can lead to unexpected slow downs when the cache is
+being cleared and refilled.
+
+There is an admin check trying to detect too low memory sizing, but make sure to
+monitor the APCu cache status to see if the cache is full and if you need to
+increase the size. `APCu provides a script
+<https://github.com/krakjoe/apcu/blob/master/apc.php>`_ that can help with this,
+otherwise the `serverinfo app <https://github.com/nextcloud/serverinfo>`_ in
+Nextcloud can also show the APCu cache status.
+
 Redis
 -----
 

admin_manual/release_notes/index.rst

@@ -14,6 +14,7 @@ These sub pages will cover the most important changes in Nextcloud, as well as s
 .. toctree::
    :maxdepth: 1
 
+   upgrade_to_31.rst
    upgrade_to_30.rst
    upgrade_to_28.rst
    upgrade_to_27.rst

admin_manual/release_notes/upgrade_to_31.rst

@@ -0,0 +1,13 @@
+=======================
+Upgrade to Nextcloud 31
+=======================
+
+System requirements
+-------------------
+
+* PHP 8.1 is now deprecated but still supported.
+
+PHP configuration
+-----------------
+
+We have a new setup warning to check if the memory reserved for APCu is high enough. If you see this warning, you should increase the memory reserved for APCu. You can do this by increasing the value of the ``apc.shm_size`` directive in your ``php.ini`` file. It is generally advised to review this value and increase it if necessary depending on your instance size.