Overview of Tablespaces and Datafiles

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Let us first understand the logical structure of the database before we look at the tablespace.

  • Tablespace
  • Datafiles
  • Segments
  • Extents
  • Data blocks

Tablespaces:

Oracle Database consists of one or more logical storage units called tablespace

Its collectively store all the database data.

Each tablespace consists one or more files called datafiles.

Data is collectively stored in the datafiles that constitute each tablespace of the database



Image Source: Oracle Doumentations 

 

Types of tablespaces

There are 2-types of tablespaces there

System tablespace

Non-System tablespace

 

System tablespace

System tablespace created along with database

It’s must require in all database

Should not contain user data’s

 

Non-System tablespace

Enable more flexibility in database administration

Control the amount of space to user objects

Separate data by backup requirement

 

Creating tablespace

Create tablespace <Tablespace_Name>

Datafile <Datafie_Location>

Autoextend on next 100M Maxsize 1G;

 

We can create tablespace with below parameters based on requirements

 

CREATE TABSESPACE tablespace

Minimum Extent integer [k/M]

Logging|Nologging

Online|Offline

Permanent|Temporary

 

Read Only Tablespaces

Alter tablespace <Tablespace_Name> Read Only;


How to take tablespace in offline mode:

Whenever the database is open mode we can take any tablespace to move offline mode except the system,stsaux,undo and tmp tablespace

 

Command

 

Alter tablespace <tablespace name> Offline;

Alter tablespace <tablespace name> Online;

Alter tablespace tablespace_name

[Online | Offline [Normal | Temporary | Immediate| For Recover]]

 

Normal: Flush all blocks in all datafiles in the tablespace out of the SGA

This is default option

Temporary: Performs a checkpoint for all online datafiles in the tablespace even if some files could not be written.

For Recover: Takes tablespace offline for Pont -in-time recovery

Datafile:

Each tablespace comsists of one or more files called datafiles.

All datafiles are physical structure 

A datafile can only be a part of one tablespace.

How to Move the Datafiles:

Table space must be offline mode

User OS command to move/Copy the files


Execute the below command in sql

Alter tablespace <Tablespace_name> Rename

Datafile ‘U01/oradata/<Datafile_name.dbf>’

To ‘U02/ oradata/<Datafile_name.dbf>’;


Being tablespace online mode

 

How to drop the tablespace:

We can drop the table space from the DB when tablespace and its contents are no longer required

DEROP  TABLESPACE <TALESPACE_NAME> INCLUDING CONTENTS AND DATAFILES;

TABLESPACE: Specifies name of the tablespace to be dropped

INCLUSING CONTENTS: Drop all the segments in the tablespace

AND DATAFILES: Delete the associated OS files

CASCADE CONSTRAINTS:  Drop referential integrity Constraints table outside the tablespace that refer to primary and unique keys in the tables in the dropped tablespace.


Segments

Segments is the space allocated for a specific logical storage structure within a tablespace

Tablespace may consists of one or more segments

Each segments made up of one or more extents. 


Extents:

Space is allocated to a segment by extents

One or more extents make up a segments

The DBA Can manually add extents to segments

Extents is a group of connected blocks.


Reference:

Frequently used Tablespace and datafile commands

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