METHOD AND MEANS FOR ARCHIVING MODIFIABLE PAGES IN A LOG BASED TRANSACTION MANAGEMENT SYSTEM

A method and means for achieving files of modifiable pages in a log based phased commit transaction management system (TMS) in which those pages which have been modified since the last full or incremental backup donot require during the copy operation any modifications to the page itself but merely to a common status page. This is accomplished by management of a pair of global log sequence numbers. Comparison between a first number (ICBU.sub.-- LSN) and each data page LSN as the page is modified permits the common status page to be updated to correctly reflect the changed status. Subsequent modifications to the same page donot require amendment of the status page. The status page indicia are reset as part of the backup procedure and for ascertaining the page copy set for incremental copying. The ICBU LSN assumes one of two values as a function of the copy operation and another value for processing page modifications after the copy operation. A second number (ICRF.sub.-- LSN) is used in the restoration of a file after the file has been partially restored by a page merge in page number order from full and incremental copies. In this case, the ICRF.sub.-- LSN defines the point in the log for redo since the most recent copy was made.