MySQL - error socket

Hello,

I have Hassbian last version (from 2.7.2019). How I installed MySQL:

1.sudo apt install default-mysql-server
2. Create database
sudo mysql -u root

CREATE DATABASE hass_db;
CREATE USER 'username'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON hass_db.* TO 'username'@'localhost';
FLUSH PRIVILEGES;
quit;
sudo service mysql restart
sudo apt-get install libmariadb-dev-compat libssl-dev
sudo apt-get install default-libmysqlclient-dev libssl-dev
pip3 install mysqlclient
sudo -u homeassistant -H -s
source /srv/homeassistant/bin/activate
pip3 install mysqlclient

Configuration recorder in yaml:

recorder:
  purge_keep_days: 1
  db_url: mysql://username:[email protected]/hass_db?charset=utf8
  include:
    entities:
      - sensor.livingroom_temperature
      - sensor.outdoors_temperature
      - sensor.boiler_temperature
      - sensor.wboiler_temperature
      - switch.boiler
      - switch.heating
      - switch.wboiler

The installation is successful. It works for several days, but after appears error: 2002, “Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (2)” home assistant. Saving to MySQL is broken.

Question: Is it installation correct? Can be a problem in purge_keep_days: 1, it can delete an important configuration?

Thank you.