Comment 9 for bug 1664025

Looks like juju unit agent is tied with mysqld process somehow. That's why agent upgrade (agent stop/start) causes mysql clean shutdown.

$ sudo systemctl status jujud-unit-mysql-0
● jujud-unit-mysql-0.service - juju unit agent for mysql/0
   Loaded: loaded (/var/lib/juju/init/jujud-unit-mysql-0/jujud-unit-mysql-0.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2017-02-13 09:57:30 UTC; 1min 47s ago
 Main PID: 16588 (bash)
    Tasks: 40
   Memory: 1.2G
      CPU: 4.353s
   CGroup: /system.slice/jujud-unit-mysql-0.service
           ├─16588 bash /var/lib/juju/init/jujud-unit-mysql-0/exec-start.sh
           ├─16592 /var/lib/juju/tools/unit-mysql-0/jujud unit --data-dir /var/lib/juju --unit-name mysql/0 --debug
           ├─16918 /bin/sh /usr/bin/mysqld_safe --wsrep-new-cluster
           └─17400 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/percona-xtradb-cluster --plugin-dir=/usr/lib/mysql/plugin --user=mysql --wsrep-provider=/usr/lib/libgalera_smm.so --wsrep

Feb 13 09:57:30 juju-cb5bdd-0 systemd[1]: Started juju unit agent for mysql/0.

$ sudo systemctl stop jujud-unit-mysql-0.service
$ pgrep -af mysqld
-> empty (no mysqld is running)