Are there any recommendations to keep the database healthy in a production environment ? For instance, a list of tables (or better, scripts) which should be archived and purged on a regular basis to keep performance optimal ?
Activiti keeps its runtime tables minimal, to keep things fast.
All the stuff in the history tables could be archived. There are no foreign keys from history to runtime. But it of course depends on your usage of the history: are you querying and displaying history info anywhere? If so, it might not be as easy to remove the history.
Of course, if you don't need the history, you could also turn it off completely.