How Oracle Disk Manager works with Oracle Managed Files


How Oracle Disk Manager works with Oracle Managed Files
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The following example illustrates the relationship between Oracle Disk Manager and Oracle Managed Files (OMF). The example shows the init.ora contents and the command for starting the database instance. To simplify Oracle UNDO management, the new Oracle10g or later init.ora parameter UNDO_MANAGEMENT is set to AUTO. This is known as System-Managed Undo.

Note:

Before building an OMF database, you need the appropriate init.ora default values. These values control the location of the SYSTEM tablespace, online redo logs, and control files after the CREATE DATABASE statement is executed.

$ cat initPROD.ora
UNDO_MANAGEMENT = AUTO
DB_CREATE_FILE_DEST = '/PROD'
DB_CREATE_ONLINE_LOG_DEST_1 = '/PROD'
db_block_size = 4096 
db_name = PROD
$ sqlplus /nolog
SQL> connect / as sysdba
SQL> startup nomount pfile= initPROD.ora

The Oracle instance starts.

Total System Global Area 93094616 bytes 
Fixed Size 279256 bytes
Variable Size 41943040 bytes
Database Buffers 50331648 bytes
Redo Buffers 540672 bytes

To implement a layout that places files associated with the EMP_TABLE tablespace in a directory separate from the EMP_INDEX tablespace, use the ALTER SYSTEM statement. This example shows how OMF handles file names and storage clauses and paths. The layout allows you to think of the tablespaces as objects in a file system as opposed to a collection of datafiles. Since OMF uses the Oracle Disk Manager file resize function, the tablespace files are initially created with the default size of 100MB and grow as needed. Use the MAXSIZE attribute to limit growth.

The following example shows the commands for creating an OMF database and for creating the EMP_TABLE and EMP_INDEX tablespaces in their own locale.

Note:

The directory must exist for OMF to work, so the SQL*Plus HOST command is used to create the directories:

SQL> create database PROD;

The database is created.

SQL> HOST mkdir /PROD/EMP_TABLE;
SQL> ALTER SYSTEM SET DB_CREATE_FILE_DEST = '/PROD/EMP_TABLE';

The system is altered.

SQL> create tablespace EMP_TABLE DATAFILE AUTOEXTEND ON MAXSIZE \
500M;

A tablespace is created.

SQL> ALTER SYSTEM SET DB_CREATE_FILE_DEST = '/PROD/EMP_INDEX';

The system is altered.

SQL> create tablespace EMP_INDEX DATAFILE AUTOEXTEND ON MAXSIZE \
100M;

A tablespace is created.

Use the ls command to show the newly created database:

$ ls -lFR
total 638062
drwxr-xr-x 2 oracle10g dba 96 May  3 15:43 EMP_INDEX/
drwxr-xr-x 2 oracle10g dba 96 May  3 15:43 EMP_TABLE/
-rw-r--r-- 1 oracle10g dba 104858112 May 3 17:28 ora_1_BEhYgc0m.log 
-rw-r--r-- 1 oracle10g dba 104858112 May 3 17:27 ora_2_BEhYu4NA.log
-rw-r--r-- 1 oracle10g dba 806912 May 3 15:43 ora_BEahlfUX.ctl
-rw-r--r-- 1 oracle10g dba 10489856 May 3 15:43 ora_sys_undo_BEajPSVq.dbf
-rw-r--r-- 1 oracle10g dba 104861696 May 3 15:4 ora_system_BEaiFE8v.dbf 
-rw-r--r-- 1 oracle10g dba 186 May 3 15:03 PROD.ora 

./EMP_INDEX:
total 204808
-rw-r--r-- 1 oracle10g dba 104861696 May 3 15:43
ora_emp_inde_BEakGfun.dbf

./EMP_TABLE:
total 204808
-rw-r--r-- 1 oracle10g dba 104861696 May 3 15:43
ora_emp_tabl_BEak1LqK.dbf