Managing Tablespaces : Bigfile Tablespaces

A bigfile tablespace is a tablespace with a single, but very large (up to 4G blocks) datafile. Traditional smallfile tablespaces, in contrast, can contain multiple datafiles, but the files cannot be as large. The benefits of bigfile tablespaces are the following:

• A bigfile tablespace with 8K blocks can contain a 32 terabyte datafile. A bigfile tablespace with 32K blocks can contain a 128 terabyte datafile. The maximum number of datafiles in an Oracle Database is limited (usually to 64K files). Therefore, bigfile tablespaces can significantly enhance the storage capacity of an Oracle Database.
• Bigfile tablespaces can reduce the number of datafiles needed for a database. An additional benefit is that the DB_FILES initialization parameter and MAXDATAFILES parameter of the CREATE DATABASE and CREATE CONTROLFILE statements can be adjusted to reduce the amount of SGA space required for datafile information and the size of the control file.
• Bigfile tablespaces simplify database management by providing datafile transparency. SQL syntax for the ALTER TABLESPACE statement lets you perform operations on tablespaces, rather than the underlying individual datafiles.

Bigfile tablespaces are supported only for locally managed tablespaces with automatic segment space management, with three exceptions: locally managed undo tablespaces, temporary tablespaces, and the SYSTEM tablespace.

Notes:

 Bigfile tablespaces are intended to be used with Automatic Storage Management (ASM) or other logical volume managers that supports striping or RAID, and dynamically extensible logical volumes.
 Avoid creating bigfile tablespaces on a system that does not support striping because of negative implications for parallel query execution and RMAN backup parallelization.
 Using bigfile tablespaces on platforms that do not support large file sizes is not recommended and can limit tablespace capacity. Refer to your operating system specific documentation for information about maximum supported file sizes.

Creating a Bigfile Tablespace
To create a bigfile tablespace, specify the BIGFILE keyword of the CREATE TABLESPACE statement (CREATE BIGFILE TABLESPACE ...). Oracle Database automatically creates a locally managed tablespace with automatic segment space management.
You can, but need not, specify EXTENT MANAGEMENT LOCAL and SEGMENT SPACE
MANAGEMENT AUTO in this statement. However, the database returns an error if you specify EXTENT MANAGEMENT DICTIONARY or SEGMENT SPACE MANAGEMENT MANUAL.
The remaining syntax of the statement is the same as for the CREATE TABLESPACE
statement, but you can only specify one datafile. For example:

CREATE BIGFILE TABLESPACE bigtbs

DATAFILE '/u02/oracle/data/bigtbs01.dbf' SIZE 50G

You can specify SIZE in kilobytes (K), megabytes (M), gigabytes (G), or terabytes (T).

If the default tablespace type was set to BIGFILE at database creation, you need not specify the keyword BIGFILE in the CREATE TABLESPACE statement. A bigfile tablespace is created by default.

If the default tablespace type was set to BIGFILE at database creation, but you want to create a traditional (smallfile) tablespace, then specify a CREATE SMALLFILE TABLESPACE statement to override the default tablespace type for the tablespace that you are creating.

Altering a Bigfile Tablespace
Two clauses of the ALTER TABLESPACE statement support datafile transparency when you are using bigfile tablespaces:

• RESIZE: The RESIZE clause lets you resize the single datafile in a 
       bigfile tablespace to an absolute size, without referring to the datafile. 
       For example:

               ALTER TABLESPACE bigtbs RESIZE 80G;

               AUTOEXTEND (used outside of the ADD DATAFILE clause):

With a bigfile tablespace, you can use the AUTOEXTEND clause outside of the ADD DATAFILE clause. For example:

ALTER TABLESPACE bigtbs
AUTOEXTEND ON NEXT 20G;

An error is raised if you specify an ADD DATAFILE clause for a bigfile tablespace.

Identifying a Bigfile Tablespace

The following views contain a BIGFILE column that identifies a tablespace as a
bigfile tablespace:

• DBA_TABLESPACES
• USER_TABLESPACES
• V$TABLESPACE

You can also identify a bigfile tablespace by the relative file number of its single datafile. That number is 1024 on most platforms, but 4096 on OS/390.