1. A computer-implemented method, comprising: a main standby database system applying changes to standby database files, wherein the changes were made to a primary database of a primary database system; in response to applying changes, advancing an established logical time associated with a consistent state of the primary database system for computing queries to a particular logical time associated with a subsequent consistent state of the primary database system; sending to one or more subsidiary standby database systems said particular logical time, wherein said one or more subsidiary standby database systems do not apply said changes to said standby database files; and while said main standby database system is applying said changes to said standby database files: receiving a query issued to a subsidiary standby database system of the one or more subsidiary database systems; and said subsidiary standby database system computing results for said query that are consistent with said particular logical time based on data read from said standby database files; wherein each of the above steps is performed by one or more computing devices.