Physical Structure

An Oracle database consists of physical files.  The database itself has:

·        Datafiles – these contain the organization's actual data.

·        Redo log files – these contain a chronological record of changes made to the database, and enable recovery when failures occur.

·        Control files – these are used to synchronize all database activities and are covered in more detail in a later module.

Other key files as noted above include: 

·        Parameter file – there are two types of parameter files. 

o   The init.ora file (also called the PFILE) is a static parameter file.  It contains parameters that specify how the database instance is to start up.  For example, some parameters will specify how to allocate memory to the various parts of the system global area.

o   The spfile.ora is a dynamic parameter file.  It also stores parameters to specify how to startup a database; however, its parameters can be modified while the database is running.

·        Password file – specifies which *special* users are authenticated to startup/shut down an Oracle Instance.

·        Archived redo log files – these are copies of the redo log files and are necessary for recovery in an online, transaction-processing environment in the event of a disk failure.