is there at any point in time any data in there?
I think that deploying the same process definition multiple times will result in many versions of the definition.
Deletion of history (and not only history) happens when you undeploying process definition. When you delete running process instance, all information about this process instance (including history) will be deleted.
Yes- there is data in the tables. I haven't been able to pinpoint when the data is deleted. I thought the issue was fixed as I ran a bunch of tests and stopped the service (I thought it was a caching/persistence/transaction commit issue), and saw my data was still there. The next day, I looked at the tables again, and the data had disappeared. Therefore, I am *assuming* it must be deleted when I restart my service which redeploys the process definitions... but haven't been able to verify this yet.