The earlier build of RecentX (4.0.13) had some bug where the data files grew quite big. 500mb is little on the higher side.
Can you please download the latest update from : http://www.conceptworld.com/RecentX/Download ?
It is much more snappier than the previous version.
Please follow below steps before installing new version:
1. Exit RecentX
2. Open the folder %appdata%\Conceptworld\RecentX in Windows Explorer. To do this, copy this path %appdata%\Conceptworld\RecentX and run from start menu or open in Windows Explorer.
3. Delete all the files in that folder
Download latest version from our website and let it index the files (when the computer is idle).