First knowledge of Oracle Control Files

Source: Oracle dba ppt06 Maintaining the Control File
1. Learning Objectives
1) Explain the use of control files
2) List Control File Content
3) Diversified Management and control documents
4) use OMF to manage control files
5) Get Control File Information

2. What is a control file? What features does it have?
Definition: the control file is a binary file that defines the physical status of the current database.
Features:
1) if the control file is lost, it needs to be restored.
2) read in the MOUNT status
3) control files are constantly updated during database operation
4) each control file is associated with only one database.
5) should be diversified
6) Maintain database entities
7) size initialized by the create database statement

Note: The control file is managed and maintained by the DBA.

3. What content does the control file contain?
1) Database Name and unique database ID
2) data file and Log File ID
3) Check the Point Number of the synchronization information required for database recovery
4) database creation time
5) tablespace name
6) The current redo log file SCN
7) start and end of rollback segments
8) redo log archiving information
9) backup information

4. What is the brief introduction to the control file?
1) The control file is specified by the control_files parameter in the following format:
Control_files = ("home/app/.../control01.ctl", "home/app/.../control02.ctl ")
Each file in the parameter is an image relationship. That is to say, the database can run normally if one of the files is in good condition.

2) the following statement queries the control file information:
SQL> select * from v $ controlfile
If the control file is damaged or lost, the database will be terminated and cannot be started. Therefore, to mirror the control file, perform the following steps:
A. Close the database.
B. Copy the control file
C. Modify the parameter file and add the location description of the new control file.
D. Restart the database.
Note that the control file also contains several server parameter settings. If you modify the value of these parameters, you just need to re-create the control file. These parameters are:
MAXLOGFILES: Maximum number of log files
MAXLOGMEMBERS: Maximum number of log members
MAXLOGHISTORY: Maximum number of historical logs
MAXDATAFILES: Maximum number of data files
MAXINSTANCES: Maximum number of instance files
All commands used to modify the database structure will change the control file. At the same time, it is recorded in the oracle trace file. The trace file name is alter_SID.log, and the path is as follows:
D: \ oracle \ product \ 10.1.0 \ admin \ DB_NAME \ bdump \ SIDALRT. log (unix is alter_SID.ora)
You can also specify the path of the trace file in the parameter file. The directory of the background process trace file is specified by the background_dump_dest parameter. The location of the user trace file is specified by the parameter user_bdump_dest, for example:
Background_bdump_dest =/u01/app/oracle/oralog/bdump
User_bdump_dest =/u01/app // oralog/udump

5. How to diversify control documents?
Steps:
1) Modify SPFILE:
Alter system set control files =
'$ HOME/ORADATA/u01/ctrl01.ctl ',
'$ HOME/ORADATA/u02/ctrl02.ctl' SCOPE = SPFILE;

2) shut down the database
SQL> shutdown

3) create additional control files
$ Cp $ HOME/ORADATA/u01/ctrl01.ctl copy the existing control file
$ HOME/ORADATA/u02/ctrl02.ctl
4) Start the database
SQL> startup

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