Using log entries, the database system logs all transactions that change data in the database. There are undo log entries (before images) and redo log entries (after images).
The database system needs the log entries to be able to undo SQL statements or to restore after a system failure (transaction consistency).
Name |
Alternative Name |
Use |
---|---|---|
Undo Log Entries |
Before Images |
|
Redo Log Entries |
After Images |
|
Concepts of the Database System, How Databases Log Data Changes
Database Administration, Backing up Log Entries