ORACLE-基础六(TABLESPACE AND DataFiles)

Tablespaces & DataFiles

Oracle stores data logically in tablespaces and physically in data files

Tablespaces:

1.Can belong to only one dataase at a time

2. Consist of one or more data files

3. Are further divied into locgical units of starage

Data files:

1.Can belong to only one tablespace and one database

2. Are a repository for schema object data

Types of Tablespaces

1.SYSTEM tablespace

a. Created with the database

b.Contains the data dictionary

c.Contains the SYSTEM undo segment

2.Non-SYSTEM tablespace

a.Separate segmets

b.Eases space administration

c.Controls amount of space allocated to a user

also types : permanent, undo , temporary

Space Mgmt in Tablespaces

1.Locally maaged tablespace:

a.Free extents are managed in the tablespace

b.Bitmap is used to record free extents.

c. Each bit corresponds to a block or group of blocks.

d. Bit value indicates free or used.

2.Dictionary-managed tablespace:

a. Free extents are managed by the data dictionary.

b.Appropriate tables are updated when extents are allocated or dellocated





推荐使用local Managed TS

Dictionary-Managed TS

1.Extents are managed in the data dictionary

2.Each segment stored in the tablespace can have a different storage clause.

3.Coalescing is required

CREATE TABLESPACE userdata DATAFILE 'xxxx.dbf' SIZE 500M EXTENT MANAGEMENT DICTIONARY DEFAULT STORAGE(initial 1M NEXT 1M PCTINCREASE 0)

</pre><h1 class="sql" name="code">Locally Managed Tablespace</h1><span style="font-size:18px;"></span><pre class="sql" name="code">1.Reduce contention on data dictionary tables

2.No undo generated when space allocation or deallocation occurs

3.No coalescing required

<pre class="sql" name="code">CREATE TABLESPACE userdata DATAFILE '/u01/oradata/userdata01.dbf' SIZE 500M EXTENT MANAGMENT LOCAL UNIFORM SIZE 128K

Migrating a DM SYSTEM TS

Migrate a dictionary manged SYSTEM tablespace to locally managed:

DBMS_SPACE_ADMIN.TABLESPACE_MIGRATE_TO_LOCAL('SYSTEM');

Undo Tablespace

1.Used to store undo segments

2.Cannot contain any other objects

3.Extents are locally namaged

4.Can only use the DATAFILE and EXTENT MANAGEMENT clauses

CREATE UNDO TABLESPACE undo1 DATAFILE '/u01/oradata/undo01.dbf' SIZE 40M

Temporary Tablespaces

1.Used for sort operations

2. Can be shared by multiple users

3.Cannot contain any permanent objects

4.Locally managed extents recommended

CREATE TEMPORARY TABLESPACE temp TEMPFILE '/u01/oradta/temp01.dbf' SIZE 20M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 4M;

Create temporary tablespace mytemp tempfile '/u01/oradata/wilson/mytemp01.dbf' size 100M extent management local;

Restrictions

Defualt tmporary tablespaces cannot be:

1.Dropped until after a new default is made available

2.Taken Offline

3.Altered to a permanent tablespace

Read-Only Tablespaces

Use the following command to place a tablespace in read-only mod:

ALTERTABLESPACE userdata READ ONLY

1.Causes a checkpoint

2.Data available only for read operations

3.Objects can be dropped from tablespace

Taking a Tablespace Offline

1.Not available for data access

2.Tablespaces that cannot be aken offline:

a.SYSTEM tablespace

b.Tablespaces with active undo segments

c.Default temporary tablespace

3.To take a tablespace offline:

ALTER TABLESPACE userdata OFFLINE

4.To bring a tablespace online:

ALTER TABLESPACE userdata ONLINE

Resizeing a Tablespace

A tablespace can be resized by :

1. Change the size of a data file:

a.Automatically using AUTOEXTEND

b.Manually using ALTER DATABASE

2.Adding a data file using ALTER TABLESPACE

Enable Automatic Extension

1.Can be resized automatically with the following commands:

a.CREATE DATABASE

b.CREATE TABLESPACE

c.ALTER TABLESPACE ... ADD DATAFILE

b.Example:

CREATE TABLESPACE user_data DATAFILE '/u01/oradata/userdata01.dbf' SIZE 200M AUTOEXTEND ON

NEXT 10M MAXSIZE 500M

c.Query the DBA_DATA_FILES view to determine whether AUTOEXTEND is enabled

Manually Resizing Date File

1.Manually increase or decrease a data file size using ALTER DATABASE

2.Resizeing a data file adds more space without adding more data files

3.Manual resizeing of a data file reclaims unused space in database

Example:

ALTER DATABASE DATAFILE '/u01/oradata/userdaa0.dbf' RESIZE 200M

Adding Data Files to a TS

Increases the space allocated to a tablespace by adding additional data files

Add DATAFILE clause is used to add a data file

Example:

ALTER TABLESPACE user_data ADD DATAFILE '/u01/oradata/userdata03.dbf' SIZE 200M

Methods for Moving DF

1.ALTER TABLESPACE

a.TABLESPACE must be offline.

b. Target data files must exist

ALTER TABLESPACE userdate RENAME DATAFILE '/u01/oradata/allan/1.dbf' TO '/u01/radata/allan/2.dbf'

2.ALTER DATABASE

a. Database must be mountd

b.Targe datafile must exit

ALTER DATABASE RENAME FILE '/u01/oradata/system01.dbf' TO '/u01/oradata/system02.dbf'

Dropping Tablespaces

1.You cannot drop a tablespace if it:

a.Is the SYSTEM tablespace

b. Has active segments

2.INCLUDING CONTENTS drops the segments

3.INCLUDING CONTENTS AND DATAFILES deletes data files

4.CASCADE CONSTRAINTS drops all referential integrity constraints.

DROP TABLESPACE userdata INCLUDING CONTENTS AND DATAFILES;

GEt Tablespace Information

Obtaining tablespace and data file information can be obtained by querying the following:

1.Tablespace information:

a.DBA_TABLESPACES

b.v$TABLESPACE

2.Data file information:

a.DBA_DATA_FILES

b.V$DATAFILE

3.Temp file information:

a. DBA_TEMP_FILES

b.V$TEMPFILE