Oracle ORACLE9I B10508-01, Руководство по установке

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Starter Database Contents
5-26 Oracle9 i Installation Guide Release 2 (9.2.0.2) for HP Alpha OpenVMS
Locating Control Files
The starter database contains three control files
.
These files are located in the
ora_root:[oradata.< db_name >]
directory
.
The files
control01.ctl
,
control02.ctl
, and
control03.ctl
are automatically included in the Custom
database
.
Oracle Corporation recommends that you keep at least three control files
(on separate physical drives) for each database and set the CONTROL_FILES
initialization parameter to list each control file
.
Table 5–4 describes the database
control files.
Using Rollback Segments
Rollback segments record the old values of data that are changed by each
transaction, whether or not the transaction has been committed. Every database
contains one or more rollback segments. Use rollback segments to provide read
consistency, to roll back transactions, and to recover the database. The rollback
segments of the starter database are as follows:
■
Rollback segment
SYSTEM
is contained in tablespace
SYS
and is used by
SYS
.
■
Rollback segments _SYSSMU1$ through _SYSSMU10$ are a pool of rollback
segments that any instance can use if it requires a rollback segment. They are
contained in tablespace
UNDOTBS<n>
and are used by
PUBLIC
.
Using the Data Dictionary
The data dictionary is a protected collection of tables and views containing
reference information on the database, its structure, and its users
.
The data that is
stored in the dictionary includes the following:
Table 5–4 Database Control Files
Control Files Description
control01.ctl
control02.ctl
control03.ctl
A control file is an administrative file
.
Oracle9 i requires a
control file to start and run the database
.
The control file
records the physical structure of the database
.
For example, a
control file contains the database name, and the names and
locations of the database data files and redo log files.
See Also:
Oracle9i Database Administrator’s Guide for more
information on setting this initialization parameter value.