In order to ensure fast performance we recommend to keep up to 20 thousand books in one database. If you accumulated mush more books in single database and want to improve the performance, you can split your database into several parts.
Create a new database (File -> New Database) and select menu File -> Import -> Alfa Ebooks Manager.
Load the books, sort them and select the books you want to import. After that you can manually remove the imported books from the primary database.