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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).

Table 1: Types of Log Entries


Alternative Name


Undo Log Entries

Before Images

  • Enable the rollback of transactions that are not yet complete

  • Enable consistent views (for SAP liveCache databases only)

Redo Log Entries

After Images

  • Enable repetition of completed transactions

More Information

Concepts of the Database System, How Databases Log Data Changes

Database Administration, Backing up Log Entries