Evergreen allows for the bulk anonymization of circulation histories. Evergreen calls this aged circulation. Circulation statistics are preserved (total circs, last checkout/renewal date, checkout/renewal/checkin workstation, etc) but patron information (name : barcode) is replaced with <Aged Circulation> text and the link to the patron record is removed.

In the client, <Aged Circulation> will show in the patron field in Circulation History Tab and Show Last Few Circulations.

In the database, every time you attempt to DELETE a row from action.circ, it copies over the appropriate data to action.aged_circulation, then deletes the action.circ row.