1. A system for providing a hosted application to one or more tenants, the system comprising: a scale group having a tenant assigned thereto, the scale group configured to maintain an unshared organization database for the tenant; and one or more site-wide server computers configured to receive a request from the tenant to upgrade the hosted application and, in response to receiving the request, to place the unshared organization database into a read-only mode of operation, to migrate the unshared organization database to an upgraded scale group, to cause the unshared organization database to be upgraded, and to enable the upgraded unshared organization database for use by the tenant at the upgraded scale group.