2 Creating an Oracle Database

Planning for Database Creation

Prepare to create the database by research and careful planning. Table 2-1 lists some recommended actions:

Meeting Creation Prerequisites

Before you can create a new database, the following prerequisites must be met:

• The desired Oracle software must be installed. This includes setting various environment variables unique to your operating system and establishing the directory structure for software and database files.

• You must have the operating system privileges associated with a fully operational database administrator. You must be specially authenticated by your operating system or through a password file, allowing you to start up and shut down an instance before the database is created or opened. This authentication is discussed in "Database Administrator Authentication".

• Sufficient memory must be available to start the Oracle Database instance.

• Sufficient disk storage space must be available for the planned database on the computer that runs Oracle Database.

All of these are discussed in the Oracle Database Installation Guide specific to your operating system. If you use the Oracle Universal Installer, it will guide you through your installation and provide help in setting environment variables and establishing directory structure and authorizations.

Step 1: Decide on Your Instance Identifier (SID)

An instance is made up of the system global area (SGA) and the background processes of an Oracle Database. Decide on a unique Oracle system identifier (SID) for your instance and set the ORACLE_SID environment variable accordingly. This identifier is used to distinguish this instance from other Oracle Database instances that you may create later and run concurrently on your system.

The following example for UNIX operating systems sets the SID for the instance that you will connect to in Step 4: Connect to the Instance:

% setenv ORACLE_SID mynewdb

Step 2: Establish the Database Administrator Authentication Method

You must be authenticated and granted appropriate system privileges in order to create a database. You can use the password file or operating system authentication method. Database administrator authentication and authorization is discussed in the following sections of this book:

• "Database Administrator Security and Privileges"

• "Database Administrator Authentication"

• "Creating and Maintaining a Password File"

Step 3: Create the Initialization Parameter File

When an Oracle instance starts, it reads an initialization parameter file. This file can be a read-only text file, which must be modified with a text editor, or a read/write binary file, which can be modified dynamically by the database (for tuning) or with SQL commands that you submit. The binary file, which is preferred, is called a server parameter file. In this step, you create a text initialization parameter file. In a later step, you can optionally create a server parameter file from the text file.

One way to create the text initialization parameter file is to edit a copy of the sample initialization parameter file that Oracle provides on the distribution media, or the sample presented in this book.

$ORACLE_HOME/dbs/init.ora

For convenience, store your initialization parameter file in the Oracle Database default location, using the default name. Then when you start your database, it will not be necessary to specify the PFILE clause of the STARTUP command, because Oracle Database automatically looks in the default location for the initialization parameter file.

For name, location, and sample content for the initialization parameter file, and for a discussion of how to set initialization parameters, see "Understanding Initialization Parameters".

Step 4: Connect to the Instance

Start SQL*Plus and connect to your Oracle Database instance AS SYSDBA.

$ SQLPLUS /nolog
CONNECT SYS/password AS SYSDBA

Step 5: Create a Server Parameter File (Recommended)

Oracle recommends that you create a server parameter file. The server parameter file enables you to change initialization parameters with database commands and persist the changes across a shutdown and startup. You create the server parameter file from your edited text initialization file. For more information, see "Managing Initialization Parameters Using a Server Parameter File".

The following script creates a server parameter file from the text initialization parameter file and writes it to the default location. The script can be executed before or after instance startup, but after you connect as SYSDBA. The database must be restarted before the server parameter file takes effect.

-- create the server parameter file 
CREATE SPFILE='/u01/oracle/dbs/spfilemynewdb.ora' FROM
       PFILE='/u01/oracle/admin/initmynewdb/scripts/init.ora';
SHUTDOWN 
-- the next startup will use the server parameter file
EXIT

Step 6: Start the Instance

Start an instance without mounting a database. Typically, you do this only during database creation or while performing maintenance on the database. Use the STARTUP command with the NOMOUNT clause. In this example, because the server parameter file is stored in the default location, you are not required to specify the PFILE clause:

STARTUP NOMOUNT

At this point, the SGA is created and background processes are started in preparation for the creation of a new database. The database itself does not yet exist.

Step 7: Issue the CREATE DATABASE Statement

To create the new database, use the CREATE DATABASE statement. The following statement creates database mynewdb:

CREATE DATABASE mynewdb
   USER SYS IDENTIFIED BY pz6r58
   USER SYSTEM IDENTIFIED BY y1tz5p
   LOGFILE GROUP 1 ('/u01/oracle/oradata/mynewdb/redo01.log') SIZE 100M,
           GROUP 2 ('/u01/oracle/oradata/mynewdb/redo02.log') SIZE 100M,
           GROUP 3 ('/u01/oracle/oradata/mynewdb/redo03.log') SIZE 100M
   MAXLOGFILES 5
   MAXLOGMEMBERS 5
   MAXLOGHISTORY 1
   MAXDATAFILES 100
   MAXINSTANCES 1
   CHARACTER SET US7ASCII
   NATIONAL CHARACTER SET AL16UTF16
   DATAFILE '/u01/oracle/oradata/mynewdb/system01.dbf' SIZE 325M REUSE
   EXTENT MANAGEMENT LOCAL
   SYSAUX DATAFILE '/u01/oracle/oradata/mynewdb/sysaux01.dbf' SIZE 325M REUSE
   DEFAULT TABLESPACE tbs_1
   DEFAULT TEMPORARY TABLESPACE tempts1
      TEMPFILE '/u01/oracle/oradata/mynewdb/temp01.dbf' 
      SIZE 20M REUSE
   UNDO TABLESPACE undotbs 
      DATAFILE '/u01/oracle/oradata/mynewdb/undotbs01.dbf'
      SIZE 200M REUSE AUTOEXTEND ON MAXSIZE UNLIMITED;

A database is created with the following characteristics:

• The database is named mynewdb. Its global database name is mynewdb.us.oracle.com. See "DB_NAME Initialization Parameter" and "DB_DOMAIN Initialization Parameter".

• Three control files are created as specified by the CONTROL_FILES initialization parameter, which was set before database creation in the initialization parameter file. See "Sample Initialization Parameter File" and "Specifying Control Files".

• The password for user SYS is pz6r58 and the password for SYSTEM is y1tz5p. The two clauses that specify the passwords for SYS and SYSTEM are not mandatory in this release of Oracle Database. However, if you specify either clause, you must specify both clauses. For further information about the use of these clauses, see "Protecting Your Database: Specifying Passwords for Users SYS and SYSTEM".

• The new database has three redo log files as specified in the LOGFILE clause. MAXLOGFILES, MAXLOGMEMBERS, and MAXLOGHISTORY define limits for the redo log. See Chapter 6, "Managing the Redo Log".

• MAXDATAFILES specifies the maximum number of datafiles that can be open in the database. This number affects the initial sizing of the control file.

  Note:

  You can set several limits during database creation. Some of these limits are limited by and affected by operating system limits. For example, if you set MAXDATAFILES, Oracle Database allocates enough space in the control file to store MAXDATAFILES filenames, even if the database has only one datafile initially. However, because the maximum control file size is limited and operating system dependent, you might not be able to set all CREATE DATABASE parameters at their theoretical maximums.

  For more information about setting limits during database creation, see the Oracle Database SQL Reference and your operating system specific Oracle documentation.

• MAXINSTANCES specifies that only one instance can have this database mounted and open.

• The US7ASCII character set is used to store data in this database.

• The AL16UTF16 character set is specified as the NATIONAL CHARACTER SET, used to store data in columns specifically defined as NCHAR, NCLOB, or NVARCHAR2.

• The SYSTEM tablespace, consisting of the operating system file /u01/oracle/oradata/mynewdb/system01.dbf is created as specified by the DATAFILE clause. If a file with that name already exists, it is overwritten.

• The SYSTEM tablespace is a locally managed tablespace. See "Creating a Locally Managed SYSTEM Tablespace".

• A SYSAUX tablespace is created, consisting of the operating system file /u01/oracle/oradata/mynewdb/sysaux01.dbf as specified in the SYSAUX DATAFILE clause. See "Creating the SYSAUX Tablespace".

• The DEFAULT TABLESPACE clause creates and names a default permanent tablespace for this database.

• The DEFAULT TEMPORARY TABLESPACE clause creates and names a default temporary tablespace for this database. See "Creating a Default Temporary Tablespace".

• The UNDO TABLESPACE clause creates and names an undo tablespace that is used to store undo data for this database if you have specified UNDO_MANAGEMENT=AUTO in the initialization parameter file. See "Using Automatic Undo Management: Creating an Undo Tablespace".

• Redo log files will not initially be archived, because the ARCHIVELOG clause is not specified in this CREATE DATABASE statement. This is customary during database creation. You can later use an ALTER DATABASE statement to switch to ARCHIVELOG mode. The initialization parameters in the initialization parameter file for mynewdb relating to archiving are LOG_ARCHIVE_DEST_1 and LOG_ARCHIVE_FORMAT. See Chapter 7, "Managing Archived Redo Logs".

  See Also:

  • "Understanding the CREATE DATABASE Statement"

  • Oracle Database SQL Reference for more information about specifying the clauses and parameter values for the CREATE DATABASE statement

Step 8: Create Additional Tablespaces

To make the database functional, you need to create additional files and tablespaces for users. The following sample script creates some additional tablespaces:

CONNECT SYS/password AS SYSDBA
-- create a user tablespace to be assigned as the default tablespace for users
CREATE TABLESPACE users LOGGING 
     DATAFILE '/u01/oracle/oradata/mynewdb/users01.dbf' 
     SIZE 25M REUSE AUTOEXTEND ON NEXT  1280K MAXSIZE UNLIMITED 
     EXTENT MANAGEMENT LOCAL;
-- create a tablespace for indexes, separate from user tablespace
CREATE TABLESPACE indx LOGGING 
     DATAFILE '/u01/oracle/oradata/mynewdb/indx01.dbf' 
     SIZE 25M REUSE AUTOEXTEND ON NEXT  1280K MAXSIZE UNLIMITED 
     EXTENT MANAGEMENT LOCAL;

For information about creating tablespaces, see Chapter 8, "Managing Tablespaces".

Step 9: Run Scripts to Build Data Dictionary Views

Run the scripts necessary to build views, synonyms, and PL/SQL packages:

CONNECT SYS/password AS SYSDBA
@/u01/oracle/rdbms/admin/catalog.sql
@/u01/oracle/rdbms/admin/catproc.sql
EXIT

The following table contains descriptions of the scripts:

Step 10: Run Scripts to Install Additional Options (Optional)

You may want to run other scripts. The scripts that you run are determined by the features and options you choose to use or install. Many of the scripts available to you are described in the Oracle Database Reference.

If you plan to install other Oracle products to work with this database, see the installation instructions for those products. Some products require you to create additional data dictionary tables. Usually, command files are provided to create and load these tables into the database data dictionary.

See your Oracle documentation for the specific products that you plan to install for installation and administration instructions.

Step 11: Back Up the Database.

Take a full backup of the database to ensure that you have a complete set of files from which to recover if a media failure occurs. For information on backing up a database, see Oracle Database Backup and Recovery Basics.

Specifying the Default Tablespace Type

The SET DEFAULT...TABLESPACE clause of the CREATE DATABASE statement to determines the default type of tablespace for this database in subsequent CREATE TABLESPACE statements. Specify either SET DEFAULT BIGFILE TABLESPACE or SET DEFAULT SMALLFILE TABLESPACE. If you omit this clause, the default is a smallfile tablespace, which is the traditional type of Oracle Database tablespace. A smallfile tablespace can contain up to 1022 files with up to 4M blocks each.

The use of bigfile tablespaces further enhances the Oracle-managed files feature, because bigfile tablespaces make datafiles completely transparent for users. SQL syntax for the ALTER TABLESPACE statement has been extended to allow you to perform operations on tablespaces, rather than the underlying datafiles.

The CREATE DATABASE statement shown in "Specifying Oracle-Managed Files at Database Creation" can be modified as follows to specify that the default type of tablespace is a bigfile tablespace:

CREATE DATABASE rbdb1
     USER SYS IDENTIFIED BY pz6r58
     USER SYSTEM IDENTIFIED BY y1tz5p
     SET DEFAULT BIGFILE TABLESPACE
     UNDO TABLESPACE undotbs
     DEFAULT TEMPORARY TABLESPACE tempts1;

To dynamically change the default tablespace type after database creation, use the SET DEFAULT TABLESPACE clause of the ALTER DATABASE statement:

ALTER DATABASE SET DEFAULT BIGFILE TABLESPACE;

You can determine the current default tablespace type for the database by querying the DATABASE_PROPERTIES data dictionary view as follows:

SELECT PROPERTY_VALUE FROM DATABASE_PROPERTIES 
   WHERE PROPERTY_NAME = 'DEFAULT_TBS_TYPE';

Overriding the Default Tablespace Type

The SYSTEM and SYSAUX tablespaces are always created with the default tablespace type. However, you can explicitly override the default tablespace type for the UNDO and DEFAULT TEMPORARY tablespace during the CREATE DATABASE operation.

For example, you can create a bigfile UNDO tablespace in a database with the default tablespace type of smallfile as follows:

CREATE DATABASE rbdb1
...
     BIGFILE UNDO TABLESPACE undotbs
        DATAFILE '/u01/oracle/oradata/mynewdb/undotbs01.dbf'
        SIZE 200M REUSE AUTOEXTEND ON MAXSIZE UNLIMITED;

You can create a smallfile DEFAULT TEMPORARY tablespace in a database with the default tablespace type of bigfile as follows:

CREATE DATABASE rbdb1
   SET DEFAULT BIGFILE TABLSPACE
...
     SMALLFILE DEFAULT TEMPORARY TABLESPACE tempts1
        TEMPFILE '/u01/oracle/oradata/mynewdb/temp01.dbf' 
        SIZE 20M REUSE
...

Setting the Database Time Zone

Set the database time zone when the database is created by using the SET TIME_ZONE clause of the CREATE DATABASE statement. If you do not set the database time zone, then it defaults to the time zone of the server's operating system.

You can change the database time zone for a session by using the SET TIME_ZONE clause of the ALTER SESSION statement.

Specifying the Database Time Zone File

Two time zone files are included in the Oracle home directory. The default time zone file is $ORACLE_HOME/oracore/zoneinfo/timezonelrg.dat. A smaller time zone file can be found in $ORACLE_HOME/oracore/zoneinfo/timezone.dat.

If you are already using the smaller time zone file and you want to continue to use it in an Oracle Database 10g environment or if you want to use the smaller time zone file instead of the default time zone file, then complete the following tasks:

1. Shut down the database.

2. Set the ORA_TZFILE environment variable to the full path name of the timezone.dat file.

3. Restart the database.

If you are already using the default time zone file, then it is not practical to change to the smaller time zone file because the database may contain data with time zones that are not part of the smaller time file.

All databases that share information must use the same time zone datafile.

The time zone files contain the valid time zone names. The following information is also included for each time zone:

• Offset from Coordinated Universal Time (UTC)

• Transition times for Daylight Saving Time

• Abbreviations for standard time and Daylight Saving Time

To view the time zone names in the file being used by your database, use the following query:

SELECT * FROM V$TIMEZONE_NAMES;

Using the FORCE LOGGING Clause

To put the database into FORCE LOGGING mode, use the FORCE LOGGING clause in the CREATE DATABASE statement. If you do not specify this clause, the database is not placed into FORCE LOGGING mode.

Use the ALTER DATABASE statement to place the database into FORCE LOGGING mode after database creation. This statement can take a considerable time for completion, because it waits for all unlogged direct writes to complete.

You can cancel FORCE LOGGING mode using the following SQL statement:

ALTER DATABASE NO FORCE LOGGING;

Independent of specifying FORCE LOGGING for the database, you can selectively specify FORCE LOGGING or NO FORCE LOGGING at the tablespace level. However, if FORCE LOGGING mode is in effect for the database, it takes precedence over the tablespace setting. If it is not in effect for the database, then the individual tablespace settings are enforced. Oracle recommends that either the entire database is placed into FORCE LOGGING mode, or individual tablespaces be placed into FORCE LOGGING mode, but not both.

The FORCE LOGGING mode is a persistent attribute of the database. That is, if the database is shut down and restarted, it remains in the same logging mode. However, if you re-create the control file, the database is not restarted in the FORCE LOGGING mode unless you specify the FORCE LOGGING clause in the CREATE CONTROL FILE statement.

Performance Considerations of FORCE LOGGING Mode

FORCE LOGGING mode results in some performance degradation. If the primary reason for specifying FORCE LOGGING is to ensure complete media recovery, and there is no standby database active, then consider the following:

• How many media failures are likely to happen?

• How serious is the damage if unlogged direct writes cannot be recovered?

• Is the performance degradation caused by forced logging tolerable?

If the database is running in NOARCHIVELOG mode, then generally there is no benefit to placing the database in FORCE LOGGING mode. Media recovery is not possible in NOARCHIVELOG mode, so if you combine it with FORCE LOGGING, the result may be performance degradation with little benefit.

DB_NAME Initialization Parameter

DB_NAME must be set to a text string of no more than eight characters. During database creation, the name provided for DB_NAME is recorded in the datafiles, redo log files, and control file of the database. If during database instance startup the value of the DB_NAME parameter (in the parameter file) and the database name in the control file are not the same, the database does not start.

DB_DOMAIN Initialization Parameter

DB_DOMAIN is a text string that specifies the network domain where the database is created. This is typically the name of the organization that owns the database. If the database you are about to create will ever be part of a distributed database system, give special attention to this initialization parameter before database creation.

DB_BLOCK_SIZE Initialization Parameter

The most commonly used block size should be picked as the standard block size. In many cases, this is the only block size that you need to specify. Typically, DB_BLOCK_SIZE is set to either 4K or 8K. If you do not set a value for this parameter, the default data block size is operating system specific, which is generally adequate.

You cannot change the block size after database creation except by re-creating the database. If the database block size is different from the operating system block size, ensure that the database block size is a multiple of the operating system block size. For example, if your operating system block size is 2K (2048 bytes), the following setting for the DB_BLOCK_SIZE initialization parameter is valid:

DB_BLOCK_SIZE=4096

A larger data block size provides greater efficiency in disk and memory I/O (access and storage of data). Therefore, consider specifying a block size larger than your operating system block size if the following conditions exist:

• Oracle Database is on a large computer system with a large amount of memory and fast disk drives. For example, databases controlled by mainframe computers with vast hardware resources typically use a data block size of 4K or greater.

• The operating system that runs Oracle Database uses a small operating system block size. For example, if the operating system block size is 1K and the default data block size matches this, the database may be performing an excessive amount of disk I/O during normal operation. For best performance in this case, a database block should consist of multiple operating system blocks.

  See Also:

  Your operating system specific Oracle documentation for details about the default block size.

Nonstandard Block Sizes

Tablespaces of nonstandard block sizes can be created using the CREATE TABLESPACE statement and specifying the BLOCKSIZE clause. These nonstandard block sizes can have any of the following power-of-two values: 2K, 4K, 8K, 16K or 32K. Platform-specific restrictions regarding the maximum block size apply, so some of these sizes may not be allowed on some platforms.

To use nonstandard block sizes, you must configure subcaches within the buffer cache area of the SGA memory for all of the nonstandard block sizes that you intend to use. The initialization parameters used for configuring these subcaches are described in the next section, "Managing the System Global Area (SGA)".

The ability to specify multiple block sizes for your database is especially useful if you are transporting tablespaces between databases. You can, for example, transport a tablespace that uses a 4K block size from an OLTP environment to a data warehouse environment that uses a standard block size of 8K.

Components and Granules in the SGA

The SGA comprises a number of memory components, which are pools of memory used to satisfy a particular class of memory allocation requests. Examples of memory components include the shared pool (used to allocate memory for SQL and PL/SQL execution), the java pool (used for java objects and other java execution memory), and the buffer cache (used for caching disk blocks). All SGA components allocate and deallocate space in units of granules. Oracle Database tracks SGA memory use in internal numbers of granules for each SGA component.

The memory for dynamic components in the SGA is allocated in the unit of granules. Granule size is determined by total SGA size. Generally speaking, on most platforms, if the total SGA size is equal to or less than 1 GB, then granule size is 4 MB. For SGAs larger than 1 GB, granule size is 16 MB. Some platform dependencies may arise. For example, on 32-bit Windows NT, the granule size is 8 MB for SGAs larger than 1 GB. Consult your operating system specific documentation for more details.

You can query the V$SGAINFO view to see the granule size that is being used by an instance. The same granule size is used for all dynamic components in the SGA.

If you specify a size for a component that is not a multiple of granule size, Oracle Database rounds the specified size up to the nearest multiple. For example, if the granule size is 4 MB and you specify DB_CACHE_SIZE as 10 MB, the database actually allocates 12 MB.

Limiting the Size of the SGA

The SGA_MAX_SIZE initialization parameter specifies the maximum size of the System Global Area for the lifetime of the instance. You can dynamically alter the initialization parameters affecting the size of the buffer caches, shared pool, large pool, Java pool, and streams pool but only to the extent that the sum of these sizes and the sizes of the other components of the SGA (fixed SGA, variable SGA, and redo log buffers) does not exceed the value specified by SGA_MAX_SIZE.

If you do not specify SGA_MAX_SIZE, then Oracle Database selects a default value that is the sum of all components specified or defaulted at initialization time. If you do specify SGA_MAX_SIZE, and at the time the database is initialized the value is less than the sum of the memory allocated for all components, either explicitly in the parameter file or by default, then the database ignores the setting for SGA_MAX_SIZE.

Using Automatic Shared Memory Management

You enable the automatic shared memory management feature by setting the SGA_TARGET parameter to a non-zero value. This parameter in effect replaces the parameters that control the memory allocated for a specific set of individual components, which are now automatically and dynamically resized (tuned) as needed.

The SGA_TARGET initialization parameter reflects the total size of the SGA. Table 2-3 lists the SGA components for which SGA_TARGET includes memory—the automatically sized SGA components—and the initialization parameters corresponding to those components.

The parameters listed in Table 2-4, if they are set, take their memory from SGA_TARGET, leaving what is available for the components listed in Table 2-3.

In addition to setting SGA_TARGET to a non-zero value, you must set the value of all automatically sized SGA components to zero to enable full automatic tuning of these components.

Alternatively, you can set one or more of the automatically sized SGA components to a non-zero value, which is then used as the minimum setting for that component during SGA tuning. This is discussed in detail later in this section.

The V$SGA_TARGET_ADVICE view provides information that helps you decide on a value for SGA_TARGET. For more information, see Oracle Database Performance Tuning Guide.

SELECT SUM(value) FROM V$SGA = 1200M
SELECT CURRENT_SIZE FROM V$SGA_DYNAMIC_FREE_MEMORY = 208M

ALTER SYSTEM SET SGA_TARGET = 992M;
ALTER SYSTEM SET SHARED_POOL_SIZE = 0;
ALTER SYSTEM SET LARGE_POOL_SIZE = 0;
ALTER SYSTEM SET JAVA_POOL_SIZE = 0;
ALTER SYSTEM SET DB_CACHE_SIZE = 0;
ALTER SYSTEM SET STREAMS_POOL_SIZE = 0;

Using Manual Shared Memory Management

If you decide not to use automatic shared memory management by not setting the SGA_TARGET parameter, you must manually configure each component of the SGA. This section provides guidelines on setting the parameters that control the size of each SGA components.

DB_BLOCK_SIZE=4096

DB_CACHE_SIZE=12M
DB_2K_CACHE_SIZE=8M
DB_8K_CACHE_SIZE=4M