Tablespace

From Oracle FAQ

A tablespace is a container for segments (tables, indexes, etc). A database consists of one or more tablespaces, each made up of one or more data files. Tables and indexes are created within a particular tablespace.

Oracle has a limit of 64,000 data files per database.

Contents 1 Default tablespaces 2 Tablespace types 2.1 Permanent tablespaces 2.2 Temp tablespaces 2.3 Undo tablespaces 3 Assign tablespaces to users 4 Check free/used space per tablespace 5 Best practices 6 Also see

[edit] Default tablespaces

When a new database is created, it will have the following tablespaces (as created by the Database Configuration Assistant):

• SYSTEM (the data dictionary)
• SYSAUX (optional database components)
• TEMP (temporary tablespace, see tablespace types below)
• UNDOTBS1 (undo tablespace, see tablespace types below)
• USERS (default users tablespace created)

[edit] Tablespace types

Different tablespace types can be created for different purposes:

[edit] Permanent tablespaces

Permanent tablespaces are used to store user data and user created objects like tables, indexes and materialized views. Sample create statements:

CREATE TABLESPACE tools DATAFILE '/u01/oradata/orcl/tools/file_1.dbf' SIZE 100M;

CREATE TABLESPACE tools DATAFILE 'C:\ORA\tools01.dbf' SIZE 100M AUTOEXTEND ON MAXSIZE 500M;

[edit] Temp tablespaces

Temp or temporary tablespaces are used to store data with short lifespan (transient data), for example: global temporarily tables or sort results.

CREATE TEMPORARY TABLESPACE temp TEMPFILE '/u01/oradata/orcl/temp/file_1.dbf' SIZE 100M;

With a single temp tablespace, the database will only write to one temp file at a time. However, Temporary tablespace groups, an Oracle 10g feature, can be created to allow Oracle to write to multiple temp files simultaneously.

[edit] Undo tablespaces

Undo tablespaces are used to store "before image" data that can be used to undo transactions. See ROLLBACK.

CREATE UNDO TABLESPACE undots DATAFILE '/u01/oradata/orcl/undo/file_1.dbf' SIZE 20M;

[edit] Assign tablespaces to users

Users cannot create objects in a tablespace (even it's their default tablespace) unless they have a quota on it (or UNLIMITED TABLESPACE privilege). Some examples:

Grant user scott access to use all space in the tools tablespace:

ALTER USER scott QUOTA UNLIMITED ON tools;

Prevent user scott from using space in the system tablespace:

ALTER USER scott QUOTA 0 ON system;

[edit] Check free/used space per tablespace

Example query to check free and used space per tablespace:

SELECT /* + RULE */  df.tablespace_name "Tablespace",
       df.bytes / (1024 * 1024) "Size (MB)",
       SUM(fs.bytes) / (1024 * 1024) "Free (MB)",
       Nvl(Round(SUM(fs.bytes) * 100 / df.bytes),1) "% Free",
       Round((df.bytes - SUM(fs.bytes)) * 100 / df.bytes) "% Used"
  FROM dba_free_space fs,
       (SELECT tablespace_name,SUM(bytes) bytes
          FROM dba_data_files
         GROUP BY tablespace_name) df
 WHERE fs.tablespace_name (+)  = df.tablespace_name
 GROUP BY df.tablespace_name,df.bytes
UNION ALL
SELECT /* + RULE */ df.tablespace_name tspace,
       fs.bytes / (1024 * 1024),
       SUM(df.bytes_free) / (1024 * 1024),
       Nvl(Round((SUM(fs.bytes) - df.bytes_used) * 100 / fs.bytes), 1),
       Round((SUM(fs.bytes) - df.bytes_free) * 100 / fs.bytes)
  FROM dba_temp_files fs,
       (SELECT tablespace_name,bytes_free,bytes_used
          FROM v$temp_space_header
         GROUP BY tablespace_name,bytes_free,bytes_used) df
 WHERE fs.tablespace_name (+)  = df.tablespace_name
 GROUP BY df.tablespace_name,fs.bytes,df.bytes_free,df.bytes_used
 ORDER BY 4 DESC;

Sample output:

Tablespace                      Size (MB)  Free (MB)     % Free     % Used
------------------------------ ---------- ---------- ---------- ----------
UNDOTBS1                               65    17.8125         27         73
EXAMPLE                               100     22.625         23         77
USERS                                   5     1.0625         21         79
TEMP                                   20          2         10         90
SYSAUX                            625.125       54.5          9         91
SYSTEM                                700     9.0625          1         99

[edit] Best practices

• Do not create objects in the SYSTEM tablespace. The system tablespace is reserved for the data dictionary.
• Don't create tablespaces, with hundreds of small datafiles, these files needs to be checkpointed, resulting is unnecessary processing.

[edit] Also see

• Bigfile tablespaces - tablespaces with a single large datafile
• LMT - Locally Managed Tablespaces
• DMT - Dictionary Managed Tablespaces
• Add space to database
• Database Concepts and Architecture
• ASM - Automated Storage Management
• RAID and JBOD

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