Wordpress uses a MySQL-database. Your posts, pages, users, settings and many more things are stored in this database.
When your WordPress-website is growing, your database grows with it. There is a chance that something can go wrong, for example: messages that have been deleted on the site but are still stored in the database. These things can go wrong on any website, whether it is a WordPress site or not. Luckily WordPress has a standard function to ''repair'' or ''optimize'' your database.
Repair or optimize your WordPress database
To make sure your database can be repaired or optimized you need to add one line of code to your wp-config.php file. This is not enabled by default, because the repair page is public and can be accessed by anyone. If this function would always be on, hackers and/or bots could exploit it for their own gains. You can temporarily add this line of code to your wp-config file and remove it whenever you are done with the reparation/optimization of the database.
After you have added this, you can go to this page:
On this page, you can give WordPress the order to automatically repair and/or optimize your database.
When you are done optimizing and/or repairing your database, remove the line of code from the wp-config.php file you have added before.
On a side note: whenever you are making changes to the database, it is highly recommended to backup the database!