Comment 2 for bug 874409

Progress indicators are these spinning wheels, the digits progressing slowly from 0 to 100 (%) and all that stuff. As the manpage says quiet level 1 "produces output suitable for logging" thousands of lines saying
Reading package lists... 0%
Reading package lists... 0%
Reading package lists... 1%
Reading package lists... 2%
…
aren't that useful and are therefore what is disabled (=thousand of lines as removing previous lines isn't possible on non-tty output). One line telling what is currently done on the other hand is suitable for logging and useful in some cases.

Btw "mysql-server is already the newest version." is not an error message. It is just an information for the user - the command keeps the promise "After the command packge mysql-server is installed" for the user, that it doesn't need to do anything for it isn't an error…