docs: add docs

Author: kenjis

user_guide_src/source/changelogs/v4.4.0.rst

@@ -222,8 +222,10 @@ Others
     - It can also take an object that implements ``ResponseInterface`` as its first argument.
     - It implements ``ResponsableInterface``.
 - **DebugBar:** Now :ref:`view-routes` are displayed in *DEFINED ROUTES* on the *Routes* tab.
-- **Factories:** You can now define the classname that will actually be loaded.
-  See :ref:`factories-defining-classname-to-be-loaded`.
+- **Factories:**
+    - You can now define the classname that will actually be loaded.
+      See :ref:`factories-defining-classname-to-be-loaded`.
+    - The Config Caching implemented. See :ref:`factories-config-caching` for details.
 
 Message Changes
 ***************

user_guide_src/source/concepts/factories.rst

@@ -262,3 +262,81 @@ that single call will return a new or shared instance:
 
 .. literalinclude:: factories/007.php
    :lines: 2-
+
+.. _factories-config-caching:
+
+Config Caching
+**************
+
+.. versionadded:: 4.4.0
+
+To improve performance, the Config Caching has been implemented.
+
+Prerequisite
+============
+
+.. important:: Using this feature when the prerequisites are not met will prevent
+    CodeIgniter from operating properly. Do not use this feature in such cases.
+
+- To use this feature, the properties of all Config objects instantiated in
+  Factories must not be modified after instantiation. Put another way, the Config
+  classes must be an immutable or readonly classes.
+- By default, every Config class that is cached must implement ``__set_state()``
+  method.
+
+How It Works
+============
+
+- Save the all Config instances in Factories into a cache file before shutdown,
+  if the state of the Config instances in Factories changes.
+- Restore cached Config instances before CodeIgniter initialization if a cache
+  is available.
+
+Simply put, all Config instances held by Factories are cached immediately prior
+to shutdown, and the cached instances are used permanently.
+
+How to Update Config Values
+===========================
+
+Once cached, the cache is never expired. Changing a existing Config file
+(or changing Environment Variables for it) will not update the cache nor the Config
+values.
+
+So if you want to update Config values, update Config files or Environment Variables
+for them, and you must manually delete the cache file.
+
+You can use the ``spark cache:clear`` command:
+
+.. code-block:: console
+
+    php spark cache:clear
+
+Or simply delete the **writable/cache/FactoriesCache_config** file.
+
+How to Enable Config Caching
+============================
+
+Uncomment the following code in **public/index.php**::
+
+    --- a/public/index.php
+    +++ b/public/index.php
+    @@ -49,8 +49,8 @@ if (! defined('ENVIRONMENT')) {
+     }
+
+     // Load Config Cache
+    -// $factoriesCache = new \CodeIgniter\Cache\FactoriesCache();
+    -// $factoriesCache->load('config');
+    +$factoriesCache = new \CodeIgniter\Cache\FactoriesCache();
+    +$factoriesCache->load('config');
+     // ^^^ Uncomment these lines if you want to use Config Caching.
+
+     /*
+    @@ -79,7 +79,7 @@ $app->setContext($context);
+     $app->run();
+
+     // Save Config Cache
+    -// $factoriesCache->save('config');
+    +$factoriesCache->save('config');
+     // ^^^ Uncomment this line if you want to use Config Caching.
+
+     // Exits the application, setting the exit code for CLI-based applications

user_guide_src/source/installation/upgrade_440.rst

@@ -117,15 +117,16 @@ match the new array structure.
 Mandatory File Changes
 **********************
 
-index.php
-=========
+index.php and spark
+===================
 
-The following file received significant changes and
+The following files received significant changes and
 **you must merge the updated versions** with your application:
 
 - ``public/index.php`` (see also :ref:`v440-codeigniter-and-exit`)
+- ``spark``
 
-.. important:: If you don't update the above file, CodeIgniter will not work
+.. important:: If you don't update the above files, CodeIgniter will not work
     properly after running ``composer update``.
 
     The upgrade procedure, for example, is as follows:
@@ -134,6 +135,7 @@ The following file received significant changes and
 
         composer update
         cp vendor/codeigniter4/framework/public/index.php public/index.php
+        cp vendor/codeigniter4/framework/spark spark
 
 Config Files
 ============