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 can be
used to create a transaction-consistent database state that reflects the state
of the database system at the time of the last savepoint.
·
SAP DB OLTP: 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.