Tablespace
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.
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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)
Tablespace types
Different tablespace types can be created for different purposes:
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;
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.
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;
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;
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
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.