Does debconf-set-selections automatically deletes values from debconf database once they are used?

[Yuri Kanivetsky <yuri.kanivetsky@gmail.com>]

Hi,

One of these days, I made, say, unattended install of different
version of mysql. And the main concern is about putting passwords in
debconf database (if they are left there or not). But also I'm curious
what's exactly happening there. Consider the following typescript:

    # export DEBIAN_FRONTEND="noninteractive"

    # sudo debconf-set-selections <<< "mysql-community-server
mysql-community-server/remove-data-dir boolean true"

    # echo GET mysql-community-server/remove-data-dir | debconf-communicate
    0 true

    # apt purge mysql-*
    ...

    # echo GET mysql-community-server/remove-data-dir | debconf-communicate
    10 mysql-community-server/remove-data-dir doesn't exist

    # sudo debconf-set-selections <<< "mysql-server
mysql-server/root_password password 123456"

    # sudo debconf-set-selections <<< "mysql-server
mysql-server/root_password_again password 123456"

    # echo GET mysql-server/root_password | debconf-communicate
    0 123456

    # apt install mysql-server-5.6
    ...

    # echo GET mysql-server/root_password | debconf-communicate
    0

So, do the values get deleted after use? Who does this? Why I can set
a value when the package is not installed yet, but getting it after
removing the package triggers an error? And more importantly, is the
password still in debconf database after installing the package?

Regards,
Yuri