On a Debian Wheezy, the post install script for the package "mariadb-server-10.0" tries to call "deb-systemd-helper" which is part of the package "init-system-helpers" which isnt mandatory.

On my wheezy systems, i got this error when doing an upgrade of the packages :

Stopping MariaDB database server: mysqld.

/var/lib/dpkg/info/mariadb-server-10.0.postinst: line 270: deb-systemd-helper: command not found

Starting MariaDB database server: mysqld.

Checking for corrupt, not cleanly closed and upgrade needing tables..

Its just a "visual bug" as this command just tries to unmask the Systemd service "mysql.service" so its not breaking anything on non-systemd systems.

Adding a test to check if "deb-systemd-helper" is present on the system before executing the command would be enough.

–
On Jessie, the package also isnt mandatory but its a dependency on "cron" which is installed by default on most systems.