The database system first saves undo log files and later permanently deletes them. This function is called history management.
History management enables consistent views and asynchronous deletion of data that is no longer needed.
Only SAP liveCache database instances use consistent views. You can configure transaction consistency in OLTP (MaxDB) database instances through the isolation level.
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1. At the end of a transaction, the user task writes a reference to its undo log file in a history file in the data area.
2. History management assigns the history file to a garbage collector.
3. The garbage collector processes the history file sequentially and asks the history management which undo log files it wants to delete.
4. If an undo log file is no longer needed for a consistent view, the garbage collector deletes the undo log file and the reference to it in the history file.