During undo log management, each modifying transaction creates its own undo log file, in which the undo log entries are written. Every undo log entry is assigned an undo log sequence number starting with 0.
Undo log files are internal database storage structures, which are stored in the data area.
Storage of the undo log files in the data area means that the information in the data area is sufficient to create a transaction-consistent database state that reflects the state of the database system at the time of the last savepoint.
· MySQL MaxDB: At the end of a transaction, the transaction itself deletes the undo log files.
· SAP liveCache: At the end of the transaction, the undo log files are transferred to history management, because they are needed for unlocked, consistent reading. The undo log files are deleted at a later point in time by the garbage collector.
In exceptional circumstances, storage of the undo log files in the data area can lead to a full data area. In this case, increase the size of the data area.