What function does the VACUUM command perform in a database management system?

The VACUUM command in database management systems, such as PostgreSQL, is used for cleaning and optimizing the database. It removes 'dead' rows left after updates or deletions, freeing space and preventing the database size from growing. VACUUM also updates statistics, which helps the query optimizer to build efficient execution plans.

Example of usage:

VACUUM;

Without regular VACUUM execution, database performance may degrade due to the accumulation of unused data.