DATA RECOVERY FROM BACKUP MADE VIA A NON-DATABASE UTILITY
Original Publication Date: 2001-May-01
Included in the Prior Art Database: 2003-Jun-12
Disclosed is a technique whereby it is possible to recover a database to its current state by using the backup copy made by a non-database utility and then applying the database log. To recover from a disk failure, customers make a backup copy of the database periodically via utilities which take advantage of the device geometry, such as Hierarchical Storage Management (HSM). These utilities are outside the scope of the database system and are faster than database utilities such as image copy. DBMS maintains a log-sequence-number (LSN) in the first page of the database called the header page. (The LSN is referred to as the LSN-Header here.) DBMS updates the LSN-Header by recording the LSN of the current-end-of-log when it closes the database and at least one update was performed while the database was open. Periodically, e.g., every nth checkpoint of the database system, it records the LSN as the LSN of the restart-redo-point for every database which is open and to which at least one update has been made since the database was opened. The LSN ranges corresponding to the first update to the database and its close are maintained by DBMS and are kept in a system database called SYSLGRNG. The ranges are referred to as LSN-First-Update and LSN-Close respectively. The LSN-Close recorded is the same as the LSN-Header in the header page. These ranges are used as filters when log apply is done for recovery.