Question - When Privilege Changes Take Effect?
Answer -
When mysqld starts, all grant table contents are read into memory and become effective at that point.
Modifications to the grant tables that you perform using GRANT, REVOKE, or SET PASSWORD are noticed by the server immediately.
If you modify the grant tables manually (using INSERT, UPDATE, etc.), you should execute a FLUSH PRIVILEGES statement or run mysqladmin flush-privileges or mysqladmin reload to tell the server to reload the grant tables. Otherwise your changes will have no effect until you restart the server. If you change the grant tables manually but forget to reload the privileges, you will be wondering why your changes don't seem to make any difference!
When the server notices that the grant tables have been changed, existing client connections are affected as follows:
Table and column privilege changes take effect with the client's next request.
Database privilege changes take effect at the next USE db_name command.
Global privilege changes and password changes take effect the next time the client connects.