Databases Reference
In-Depth Information
fails, any changed database blocks that were not yet written to the datafiles are
retrieved from the redo log files and written to the datafiles when the instance is
started again.
Control Files
The
maintains information about the physical structure of the
entire database. It stores the name of the database, the names and locations of
the tablespaces in the database, the locations of the redo log files, information
about the last backup of each tablespace in the database, and much more.
Because of the importance of this file, it is recommended that a copy of the con-
trol file reside on at least three different physical disks. As with the redo log
files, Oracle keeps all copies of the control file in synch automatically.
The control file and redo log file contents do not map directly to any database
objects, but their contents and status are available to the DBA by accessing vir-
tual tables called data dictionary views, which are owned by the
control file
control file
A file that records the physical structure
of a database, the database name, and
the names and locations of datafiles and
redo log files.
SYS
schema.
Oracle Memory Structures
The memory allocated to Oracle includes the following types of data:
Data from user reading and writing activity
◆
Information about database objects
◆
SQL commands
◆
Stored procedures and functions
◆
Transaction information
◆
Oracle program executables
This information is stored in three major areas: the System Global Area
(SGA), the Program Global Area (PGA), and the Software Code Area.
◆
SGA (System Global Area)
Shared Pool
DBWn
Database buffer cache
Data dictionary cache
SMON
Shared SQL and
PL/SQL procedures
and packages
Redo Log buffer cache
LGWR
Shared
memory
Software Code Area
Non-shared
memory
PGA (Program Global Area)
