DROP USER与从mysql.user表中删除行之间的区别

I have a database with hundreds of active connections at any point in time. When I use the DROP USER sql statement to remove a user account, it takes ~4 seconds, during which all other connections have the state "Checking permissions". This means that to delete 1000 users, I'll effectively be locking the database for a good part of 4000 seconds, which is unacceptable. I do notice, however, that deleting a user row from the mysql.users table is instant.I have a database with hundreds of active conne