GD Rating System Pro 4.0 makes a huge change in the way data is stored, and it adds 3 more columns that aim to improve every aspect of the plugin working. Because of that, big parts of the rating data need to be transferred into new tables, and without that, the plugin can’t work. To make sure no new ratings are allowed, as soon as the new version is installed, the rating will be placed under maintenance, and you need to run the database upgrade.
When you get the plugin version update screen, it will go through the list of checks, update the database structure, and it will show the information about the database upgrade.
The upgrade process is very simple, and it should be done as soon as possible. Simply click the Database Upgrade button, and you will be taken to the Database 4.0 upgrade tools panel. This is a very simple panel that has only one button to start the process. Make sure you read the important notices and make sure that you have database backup ready in case something unexpected happens during the upgrade process!
The process requires the upgrade screen to remain active. It will display the upgrade process progress, and it is controlled by this page. the upgrade process is split into various smaller steps for each rating method, all upgrades are pure SQL queries, so they should be done quickly, and they should not take too much time even with a large number of ratings and votes.
Once the process finishes, you will see the message in the log about the processing being completed. After this, the maintenance mode should be disabled, but just in case, check it out in the plugin Settings -> Maintenance page.