Maintaining a database: How to optimize tables
Step 1:
Due to changes in a database such as the deletion of data sets, it can lead to fragmentation which means that unused spaces can occur between the allocated spaces. Those unused spaces are called overhead.It makes sense to optimize a database from time to time in order to re-sort the data and to erase a possibly existing overhead. In the end, this will increase the amount of free webspace.
Step 2:

This can be done directly in the KAS (Technical Administration) panel by clicking menu item Databases and the phpMyAdmin icon right next to the respective database.
Once inside the phpMyAdmin, please click the database name on the left side unless it's already selected.
Step 3:
On the right side please scroll down and click Check tables having overhead.Step 4:

Search in support and FAQ