Recover Techniques

• extensively damaged:restore backup data and redo transactions on log file

• inconsistent:use undo and redo

• deferred update:write to log file until commited then write into DB by using log records

• only redo is needed, can redo any times

• immediate update:write-ahead log protocol

• need redo and undo(reverse order)

• Shadow paging:use current and shadow page, not log file system