updateDynamicSetting now logs all changes

community/kernel/src/main/java/org/neo4j/kernel/configuration/Config.java

@@ -571,11 +571,11 @@ public Optional<?> getValue( @Nonnull String key )
      * @implNote No migration or config validation is done. If you need this you have to refactor this method.
      *
      * @param setting The setting to set to the specified value.
-     * @param value The new value to set, passing {@code null} or empty should reset the value back to default value.
+     * @param newValue The new value to set, passing {@code null} or empty should reset the value back to default value.
      * @throws IllegalArgumentException if the provided setting is unknown or not dynamic.
      * @throws InvalidSettingException if the value is not formatted correctly.
      */
-    public void updateDynamicSetting( String setting, String value ) throws IllegalArgumentException, InvalidSettingException
+    public void updateDynamicSetting( String setting, String newValue ) throws IllegalArgumentException, InvalidSettingException
     {
         // Make sure the setting is valid and is marked as dynamic
         Optional<ConfigValue> option = findConfigValue( setting );
@@ -591,19 +591,22 @@ public void updateDynamicSetting( String setting, String value ) throws IllegalA
             throw new IllegalArgumentException( "Setting is not dynamic and can not be changed at runtime" );
         }
 
-        if ( value == null || value.isEmpty() )
+        String oldValue;
+
+        if ( newValue == null || newValue.isEmpty() )
         {
             // Empty means we want to delete the configured value and fallback to the default value
-            params.remove( setting );
+            oldValue = params.remove( setting );
             if ( overriddenDefaults.containsKey( setting ) )
             {
                 params.put( setting, overriddenDefaults.get( setting ) );
             }
+            newValue = "<default value>";
         }
         else
         {
             // Change setting, make sure it's valid
-            Map<String,String> newEntry = stringMap( setting, value );
+            Map<String,String> newEntry = stringMap( setting, newValue );
             List<SettingValidator> settingValidators = configOptions.stream()
                     .map( ConfigOptions::settingGroup )
                     .collect( Collectors.toList() );
@@ -612,8 +615,13 @@ public void updateDynamicSetting( String setting, String value ) throws IllegalA
                 validator.validate( newEntry, ignore -> {} ); // Throws if invalid
             }
 
-            params.put( setting, value );
+            oldValue = params.put( setting, newValue );
+            if ( oldValue == null )
+            {
+                oldValue = "<default value>";
+            }
         }
+        log.info( "Setting changed: '%s' changed from '%s' to '%s'", setting, oldValue, newValue );
     }
 
     private Optional<ConfigValue> findConfigValue( String setting )

community/kernel/src/test/java/org/neo4j/kernel/configuration/ConfigTest.java

@@ -33,6 +33,7 @@
 import javax.annotation.Nonnull;
 
 import org.neo4j.configuration.DocumentedDefaultValue;
+import org.neo4j.configuration.Dynamic;
 import org.neo4j.configuration.Internal;
 import org.neo4j.configuration.LoadableConfig;
 import org.neo4j.configuration.ReplacedBy;
@@ -353,4 +354,28 @@ public void augmentDefaults() throws Exception
         config.augmentDefaults( MySettingsWithDefaults.hello, "new default" );
         assertEquals( "new default", config.get( MySettingsWithDefaults.hello ) );
     }
+
+    public static class MyDynamicSettings implements LoadableConfig
+    {
+        @Dynamic
+        public static final Setting<Boolean> boolSetting = setting( "bool_setting", BOOLEAN, Settings.TRUE );
+    }
+
+    @Test
+    public void updateDynamicShouldLogChanges() throws Exception
+    {
+        Config config = Config.builder().withConfigClasses( Collections.singletonList( new MyDynamicSettings() ) ).build();
+
+        Log log = mock( Log.class );
+        config.setLogger( log );
+
+        config.updateDynamicSetting( MyDynamicSettings.boolSetting.name(), "false" );
+        config.updateDynamicSetting( MyDynamicSettings.boolSetting.name(), "true" );
+        config.updateDynamicSetting( MyDynamicSettings.boolSetting.name(), "" );
+
+        verify( log ).info("Setting changed: '%s' changed from '%s' to '%s'", MyDynamicSettings.boolSetting.name(), "<default value>", "false" );
+        verify( log ).info("Setting changed: '%s' changed from '%s' to '%s'", MyDynamicSettings.boolSetting.name(), "false", "true" );
+        verify( log ).info("Setting changed: '%s' changed from '%s' to '%s'", MyDynamicSettings.boolSetting.name(), "true", "<default value>" );
+        verifyNoMoreInteractions( log );
+    }
 }