Some claim it is much faster than any other database engine available. According to the published results, MySQL outperforms all other database engines by an average of 40 percent. Of course it's best to maintain a healthy scientific skepticism. This need for speed in MySQL comes at an expense. MySQL does not support transactions.
Transactions slow down the performance of a database engine.
They also require log files so they can be undone or rolled back. Having a log file requires a system administrator to babysit the file and make sure it does not grow too large. Log files also need to be backed up with your database. A constraint is a method of enforcing relationships between tables and thereby ensuring data integrity. The main advantage of using a constraint is to guard against programming mistakes.