Data base management system for recovering from an abnormal condition

Claim 1

A data base management system comprising: a secondary storage unit having data base storing means for storing data divided into physical pages, each physical page corresponding one-to-one to a logical page; a current page table for managing position information about a latest physical page storing latest updated data and a shadow physical page storing the data before a latest update in each of the logical pages; a current page table management table for pointing to a shadow page table which is a copy of the current page table at a checkpoint, and a latest page table which is the current page table as updated after the checkpoint; blank physical page management means for managing unused physical pages in the secondary storage unit; first updating means which accesses said current page table management table when data in a logical page is updated by a transaction, said first updating means referring to management information about said blank physical page management means when a shadow page table does not exist corresponding to the page table containing the position information about the physical page corresponding to the logical page and obtaining an unused physical page, thereafter said first updating means copying the data in the latest updated page table to the physical page and enters the copied data in said current page table management table as the latest page table for the logical page and a page table before the latest update as the shadow page table, said first updating means updating said blank physical page management means to indicate the obtained physical page as being used, and checks the position information about the physical page corresponding to the logical page in said current page table according to the management information in said current page table management table, and refers to the management information in said blank physical page management means if the shadow physical page corresponding to the logical page does not exist according to the position information thereafter obtaining a presently unused physical page from said data base storing means and entering the unused physical page in said current page table as the latest physical page of the logical page; second updating means for writing the updated data of the logical page to the latest physical page corresponding to the logical page to be updated which is entered in said current page table by referring to said current page table updated by said first updating means, and changing the position information pointing to the shadow page corresponding to the logical page in said current page table such that the information points to the updated physical page; and third updating means for updating said blank physical page management means to indicate that the shadow physical page is unused.

Claim 23

A method for managing a database having a logical page with a corresponding physical page, the method comprising: shadow paging the physical page with a first shadow physical page; storing positional information in a page frame identifying the physical page and the first shadow physical page; and shadow paging the page frame with a second shadow physical page containing shadow positional information identifying the physical page and the first shadow physical page.

Claim 24

A method for managing a database having a logical page with a corresponding physical page, the method comprising: shadow paging the physical page with a first shadow physical page; storing positional information in a page frame identifying the physical page and the first shadow physical page; and shadow paging the page frame with a second shadow physical page containing shadow positional information identifying the physical page and the first shadow physical page.