More documentation (#192)

* add function has_data and remove_data

* add few rows about deleting data

* add server gone away

* formatting

* format again

Frequently-Asked-Questions.md

@@ -280,6 +280,17 @@ like `include_path = C:/Apache2/htdocs/cacti`.
 
 ## Common Problems
 
+### I see "MySQL server has gone away" in cacti log and cacti does not work as expected
+
+Check the following in MySQL/MariaDB
+```
+SHOW GLOBAL VARIABLES LIKE 'max_connections';
+SHOW GLOBAL STATUS LIKE 'max_used_connections';
+```
+
+If they are close, increase the max_connections in the server.cnf (mysql.cnf, my.cnf) 
+and restart MariaDB/MySQL.
+
 ### Cron is out of sync with the Poller Interval
 
 ```shell

Plugin-Creating-Plugins.md

@@ -42,7 +42,7 @@ setting | description
 *capabilities* | A comma delimited list of capabilities for define what capabilities the plugin has primarily remotely.
 *nosync* | A comma delimited list of relative paths that should not be synchronized with the remote data collectors, for example transient folders that may contain quite a bit of data that changes often.
 
-## Functions
+## Mandatory functions
 
 Inside the setup file, there are several functions that are mandatory in order
 for your plugin to properly be detected, and to properly function.
@@ -114,6 +114,25 @@ function plugin_PLUGINNAME_check_config () {
 }
 ```
 
+## Optional functions
+Some plugins delete all your data and settings when you uninstall them.
+However, some plugins preserve the data and can be used again in the future.
+The following 2 functions allow you to delete all data and settings without
+uninstalling the plugin or manually deleting them.
+If the plugin does not contain the function, the delete icon will not appear
+in the settings (console -> configuration -> plugins).
+These functions are used in version 1.3 and higher.
+
+```php
+function plugin_PLUGINNAME_has_data() {
+    return true;
+}
+
+function plugin_PLUGINNAME_remove_data() {
+    return false;
+}
+```
+
 #### Registering Hooks
 
 The way that your plugin is able to interact within Cacti is via the many hooks

Plugins.md

@@ -112,6 +112,11 @@ plugin.
 
 ![plugin dependencies](images/plugins-dependencies.png)
 
+### Delete plugin data and settings
+Some plugins have new functionality and allow you to delete data and plugin
+settings and start from scratcg. This can be done with the trash can icon in
+Console > Configuration > Plugins
+
 ---
 
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