DBCA Initialization Parameters Window

Use the Memory tab of the Database Configuration Assistant (DBCA) Initialization Parameters window to set the initialization parameters that control how the database manages its memory. You can choose from the following methods for memory management:

• Typical—This method requires little configuration, and allocates memory as a percentage of total overall physical system memory. Select Typical and enter a value in the Memory Size (SGA and PGA) field. The percentage of memory represented by the value entered is shown in the Percentage field. You can also use the slider to change the value. Click Show Memory Distribution to view the System Global Area (SGA) size and Program Global Area (PGA) size allocated. Click Use Automatic Memory Management to have the system automatically tunes many of the memory components of the SGA, and allocate memory to individual PGAs as needed. The system can also dynamically decrease or increase the total amount of memory allocated to the SGA or aggregate PGA, depending on processing demands. The total memory used for the database instance never exceeds the amount you specify. This automatic memory tuning for the instance is known as automatic memory management. To learn more about PGA and SGA, see "About Instance Memory Structures".

• Custom—This method requires more configuration than the Typical option, but gives you more control over how the database instance uses system memory. This option is meant for more experienced database administrators. You can directly specify memory sizes for the SGA and aggregate PGA and their substructures, such as the shared pool and buffer cache.

  Select one of the following options for customized memory management:

  • Automatic Shared Memory Management to allocate specific amounts of memory to the SGA and aggregate PGA. With this setting, automatic shared memory management is enabled for the SGA, and memory is allocated to the individual PGAs as needed.

  • Manual Shared Memory Management to enter specific values for each SGA component and the aggregate PGA. This disables automatic shared memory management and enables you to determine how the SGA memory is distributed among the SGA memory components.

In the Sizing tab of the Database Configuration Assistant (DBCA) Initialization Parameters window, you specify the smallest block size and the maximum number of operating system user processes that can simultaneously connect to the database.

• Block Size—Use this list to select the block size, or accept the default. Oracle Database data is stored in data blocks of the size specified. One data block corresponds to a specific number of bytes of physical space on disk. Selecting a block size other than the default 8 kilobytes (KB) value requires advanced knowledge and should be done only when absolutely required.

  While using predefined templates, this list is not enabled because the database will be created with the default block size of 8 KB. If you chose Custom Database in the Database Type window, you can change the block size here.

• Processes—In this field, specify the maximum number of processes that can simultaneously connect to the database. Enter a number or accept the default value of 300. The default value for this parameter is appropriate for many environments. The value you select should allow for all background processes, user processes, and parallel execution processes.

Use the Character Sets tab of the Database Configuration Assistant (DBCA) Initialization Parameters window to define the character sets used by your database. Character sets are the encoding schemes used to display characters on your computer screen. The character set determines what languages can be represented in the database.

Oracle recommends using Unicode (AL32UTF8) as the database character set. AL32UTF8 is Oracle's name for the UTF-8 encoding of the Unicode standard. The Unicode standard is the universal character set that supports most of the currently spoken languages of the world. The use of the Unicode standard is indispensable for any multilingual technology, including database processing.

After a database is created and accumulates production data, changing the database character set is a time consuming and complex project. Therefore, it is very important to select the right character set at installation time. Even if the database does not currently store multilingual data but is expected to store multilingual data within a few years, the choice of AL32UTF8 for the database character set is usually the only good decision.

If you create a multitenant container database (CDB), consider that the character set you select determines which other databases you can later plug into the CDB. Only databases with a compatible database character set can be plugged into the CDB.

The default character set used by Oracle Universal Installer (OUI) and DBCA for the UNIX, Linux, and Microsoft Windows platforms is not AL32UTF8, but a Microsoft Windows character set known as an ANSI code page. The particular character set is selected based on the current language (locale) of the operating system session that started OUI or DBCA. If the language is American English or a Western European language, then the default character set is WE8MSWIN1252. Each Microsoft Windows ANSI Code Page can store data from only one language or a limited group of languages, such as only Western European, or only Eastern European, or only Japanese.

A Microsoft Windows character set is the default even for databases created on UNIX and Linux platforms because Microsoft Windows is the prevalent platform for client workstations. Oracle Client libraries automatically perform the necessary character set conversion between the database character set and the character sets used by non-Windows client applications.

You may also choose to use any other character set from the presented list of character sets. You can use this option to select a particular character set required by an application vendor, or choose a particular character set that is the common character set used by all clients connecting to this database.

Because AL32UTF8 is a multibyte character set, database operations on character data may be slightly slower when compared to single-byte database character sets, such as WE8MSWIN1252. Storage space requirements for text in most languages that use characters outside of the ASCII repertoire are higher in AL32UTF8 compared to legacy character sets supporting the language. Note that the increase in storage space concerns only character data and only data that is not in English. The universality and flexibility of Unicode usually outweighs these additional costs.

• Database Character Set—In this section, select one of the following options:

  • Use the Default—Select this option to select only the language currently used by the operating system for all your database users and database applications.

  • Use Unicode (AL32UTF8)—Select this option to support multiple languages for your database users and database applications.

  • Choose from the list of character sets—Select this option if you want Oracle Database to use a character set other than the default character set used by the operating system.

  Note:

  AL32UTF8 is a variable-width multibyte character set. Applications connecting to a database that uses AL32UTF8 for character data processing must be correctly programmed to work with such character sets. Always verify the character set requirements of the applications that use the database. Contact the application vendor and ask for a Unicode-capable version, if your current application version does not support the Unicode standard.

• National Character Set—In this list, select a character set or accept the default. The national character set, also called NCHAR character set, is the character set used to store and process data of data types NVARCHAR2, NCHAR, and NCLOB. These data types allow storing of Unicode characters in a database that does not have a Unicode database character set. Unless installation requirements of any of your applications specify otherwise, accept the default value of AL16UTF16 as the national character set.

  Note:

  Although this character set is called "national," after the SQL standard (ISO/IEC 9075), it is not better suited to support globalized applications than the database character set. Because working with national character set data requires additional API calls in client applications, and because national character set data is not supported by some database components, such as Oracle Text, Oracle recommends that multilingual applications use VARCHAR2, CHAR, and CLOB data types and an Oracle database with the database character set AL32UTF8.

• Default Language—In this list, select a default database language or accept the default. The default language determines how the database supports locale-sensitive information such as day and month abbreviations, default sorting sequence for character data, and reading direction (left to right or right to left).

• Default Territory—In this list, select the name of the territory whose conventions are to be followed for day and week numbering or accept the default. The default territory also establishes the default date format, the default decimal character and group separator, and the default International Standardization Organization (ISO) and local currency symbols. For example, in the United Kingdom, the default date format is DD-MON-YYYY, where DD is the day of the month (1-31), MON is the abbreviated name of the month, and YYYY is the 4-digit year.

Use the Connection Mode tab of the Database Configuration Assistant (DBCA) Initialization Parameters window to select the database connection mode. You can run the database in either of the following connection modes:

• Dedicated Server Mode—This mode allows a dedicated server process for each user process. Select this option when the number of total clients is expected to be small, for example, 50 or fewer. You might also choose this option when database clients typically make persistent, long-running requests to the database. By default, the database is configured for dedicated server processes.

• Shared Server Mode—This mode allows several client connections to share a database-allocated pool of resources. Use this mode in configurations in which client load is expected to cause a strain on memory and other system resources. If you choose shared server mode, then you must indicate the number of server processes you want to create when a database instance is started. For more information about setting this parameter, click Help.