Prevent FreeRADIUS from Writing to radpostauth Table

I'm running FreeRADIUS 3 on Red Hat Linux with a MySQL backend. I want FreeRADIUS to only read from the database-no writes-since I'm syncing it to another server for redundancy and using a separate interface to manage user accounts. Everything works, but I see Access-Accept and Access-Reject entries being written to radpostauth. How can I stop this? -Mike