In its default configuration, Petclinic uses an in-memory database (HSQLDB) which
gets populated at startup with data. A similar setup is provided for MySql in case a persistent database configuration is needed.
Note that whenever the database type is changed, the app needs to be run with a different profile: spring.profiles.active=mysql
for MySql.
You could start MySql locally with whatever installer works for your OS, or with docker: