MySQL replication is used to copy data from one MySQL server (the primary or source server) to another (the replica or slave server). It is used for high availability, load balancing, and disaster recovery.

The MySQL Server processes and executes DDL (Data Definition Language) commands like CREATE, ALTER, and DROP. It communicates with the SQL Parser to interpret the commands and the storage engines to implement changes.

The Seconds_Behind_Master value, available in the output of the SHOW SLAVE STATUS command, is the default method for monitoring replication lag in MySQL. It shows how many seconds the replica is behind the primary server.

MySQL Enterprise Firewall is designed to monitor SQL query execution and block any suspicious activity or unauthorized queries, providing real-time protection against SQL injection and other database attacks.

The SHOW GRANTS command is used to display the privileges assigned to a specific user. This is helpful when checking what access levels a user has within the MySQL system.