When Is FLUSH PRIVILEGES Actually Needed in MySQL?

When to Use (and Not Use) FLUSH PRIVILEGES in MySQL

When creating new users and their associated databases, it's common to execute commands like:

CREATE DATABASE mydb;
GRANT ALL PRIVILEGES ON mydb.* TO myuser@localhost IDENTIFIED BY "mypassword";

However, it's often seen that the FLUSH PRIVILEGES command is also used after these commands in tutorials. This raises the question: when is FLUSH PRIVILEGES actually necessary?

When FLUSH PRIVILEGES is Unnecessary

As noted in the MySQL documentation, privileges assigned through GRANT do not require FLUSH PRIVILEGES to take effect. The MySQL server immediately recognizes these changes and reloads the grant tables.

When FLUSH PRIVILEGES is Necessary

FLUSH PRIVILEGES is only needed when grant tables are modified directly using commands like INSERT, UPDATE, or DELETE. In these cases, changes will not be reflected in privilege checking until the server is restarted or the grant tables are reloaded using FLUSH PRIVILEGES.

This distinction is important to understand to avoid the confusion that can arise when changes made to grant tables via direct modifications do not seem to have any effect.

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