Database Reference
In-Depth Information
Figure 3.10
Different Segment
or Tablespace Types
and Their
Functions.
the same. Thus the lines in Figure 3.10 represent those pointer links
between Controlfile, log files, and datafiles.
3.3.3
Rollback and Undo
It is important to Oracle SQL, both DML and DDL, to understand what
exactly happens when database changes are executed. Several issues need to
be covered briefly:
Transactional control.
Differences in the logging entries of DML and DDL.
Differences between the COMMIT and ROLLBACK commands.
The sequence of events when data is changed.
A transaction is a grouped (a BEGIN … END block) set of one or more
commands executed one after the other (sequentially). Dependencies may
or may not exist between commands. A transaction starts at the beginning
of a user session with the first executed command, or immediately after a
