I received several questions in the past regarding registry testing related to the Flush-On-Close functionality. So I'll talk about this a little bit in this blog.
This functionality is for the hive-based registry and it is disabled by default. When it's enabled, it will flush the registry aggresively. Basically, RegFlushKey will be called on every RegCloseKey call when Flush-On-Close is enabled. But be careful when turning on this setting, there's a tradeoff in the performance. It can degrade the performance of your system, especially if you use the registry operations a lot.
To turn on/off this feature, set the following in the registry:
This registry value is read once during the boot, thus you can't toggle the feature without a reboot.