undo log
A storage area that holds copies of data modified by active transactions. If another transaction needs to see the original data (as part of a consistent read operation), the unmodified data is retrieved from this storage area. This area is physically part of the system tablespace. It is split into separate portions, the insert undo buffer and the update undo buffer. Collectively, these parts are also known as the rollback segment, a familiar term for Oracle DBAs.
See also consistent read.
See also rollback segment.
See also system tablespace.
See also transaction.