Rename and Relocate Datafile | Oracle Database

Rename and Relocate a Datafile in Oracle Database

Renaming or Relocating Datafiles belonging to a Single Tablespace

You can rename datafiles to either change their names or relocate them.

To rename or relocate datafiles belonging to a Single Tablespace do the following.

Oracle Views to get Info About Tablespaces and Datafiles | Oracle Database

Oracle Views to get Information regarding Oracle Tablespaces and Datafiles

Oracle has provided many Data dictionary views to get information about tablespaces and datafiles.  Some of them are:

To view information about Tablespaces in a database give the following query

SQL> select * from dba_tablespaces;

SQL> select * from v$tablespace;

To view information about Datafiles

SQL> select * from dba_data_files;

SQL> select * from v$datafile;

To view information about Tempfiles

SQL> select * from dba_temp_files;

SQL> select * from v$tempfile;

To view information about free space in datafiles

SQL> select * from dba_free_space;

To view information about free space in tempfiles

SQL> select * from V$TEMP_SPACE_HEADER;

Making Tablespace Online or Offline in Oracle Database

Making Tablespace Online or Offline in Oracle Database

Taking tablespaces Offline or Online

You can take an online tablespace offline so that it is temporarily unavailable for general use. The rest of the database remains open and available for users to access data. Conversely, you can bring an offline tablespace online to make the schema objects within the tablespace available to database users. The database must be open to alter the availability of a tablespace.

We usually take tablespaces offline for maintenance purposes.

To alter the availability of a tablespace, use the ALTER TABLESPACE statement. You must have the ALTER TABLESPACE or MANAGE TABLESPACE system privilege.

To Take a Tablespace Offline give the following command

SQL> alter tablespace ica offline;

To again bring it back online give the following command.

SQL> alter tablespace ica online;

To take individual datafile offline type the following command

SQL> alter database datafile ‘/u01/oracle/ica/ica_tbs01.dbf’ offline;

Again to bring it back online give the following command

SQL> alter database datafile ‘/u01/oracle/ica/ica_tbs01.dbf’ online;

Note: You can’t take individual datafiles offline it the database is running in NOARCHIVELOG mode.  If the datafile has become corrupt or missing when the database is running in NOARCHIVELOG mode then you can only drop it by giving the following command

SQL> alter database datafile ‘/u01/oracle/ica/ica_tbs01.dbf’ offline for drop;

How to Increase the Size of Tablespace and Datafiles

How to Increase the Size of Tablespace and Datafiles

To Extend the Size of a tablespace

Option 1

 You can extend the size of a tablespace by increasing the size of an existing datafile by typing the following command

SQL> alter  database ica datafile ‘/u01/oracle/data/icatbs01.dbf’ resize

 100M;

This will increase the size from 50M to 100M

Option 2

You can also extend the size of a tablespace by adding a new datafile to a tablespace. This is useful if the size of existing datafile is reached o/s file size limit or the drive where the file is existing does not have free space. To add a new datafile to an existing tablespace give the following command.

SQL> alter tablespace add datafile  ‘/u02/oracle/ica/icatbs02.dbf’ size 

50M;

Option 3

You can also use auto extend feature of datafile. In this, Oracle will automatically increase the size of a datafile whenever space is required. You can specify by how much size the file should increase and Maximum size to which it should extend.

To make a existing datafile auto extendable give the following command

SQL> alter database datafile ‘/u01/oracle/ica/icatbs01.dbf’ auto extend 

ON next 5M maxsize 500M;

You can also make a datafile auto extendable while creating a new tablespace itself by giving the following command.

SQL> create tablespace ica datafile ‘/u01/oracle/ica/icatbs01.dbf’ size 

50M auto extend ON next 5M maxsize 500M;

To decrease the size of a tablespace

You can decrease the size of tablespace by decreasing the datafile associated with it. You decrease a datafile only up to size of empty space in it. To decrease the size of a datafile give the following command

SQL> alter database datafile ‘/u01/oracle/ica/icatbs01.dbf’ resize 30M;

Coalescing Tablespaces

A free extent in a dictionary-managed tablespace is made up of a collection of contiguous free blocks. When allocating new extents to a tablespace segment, the database uses the free extent closest in size to the required extent. In some cases, when segments are dropped, their extents are deallocated and marked as free, but adjacent free extents are not immediately recombined into larger free extents. The result is fragmentation that makes allocation of larger extents more difficult.

You should often use the ALTER TABLESPACE ... COALESCE statement to manually coalesce any adjacent free extents. To Coalesce a tablespace give the following command

SQL> alter tablespace ica coalesce;

Managing Tablespaces and Datafiles in Oracle

Tablespace And Datafile Management in Oracle - Full Explanation

Using multiple tablespaces provides several Advantages

Separate user data from data dictionary data to reduce contention among dictionary objects and schema objects for the same datafiles.

Separate data of one application from the data of another to prevent multiple applications from being affected if a tablespace must be taken offline.

Store different the datafiles of different tablespaces on different disk drives to reduce I/O contention.

Take individual tablespaces offline while others remain online, providing better overall availability.

Creating  New Tablespaces

You can create Locally Managed or Dictionary Managed Tablespaces. In prior versions of Oracle only Dictionary managed Tablespaces were available but from Oracle ver. 8i you can also create Locally Managed tablespaces. The advantages of locally managed tablespaces are

Locally managed tablespaces track all extent information in the tablespace itself by using bitmaps, resulting in the following benefits:

Concurrency and speed of space operations is improved, because space allocations and deallocations modify locally managed resources (bitmaps stored in header files) rather than requiring centrally managed resources such as enqueues

Performance is improved, because recursive operations that are sometimes required during dictionary-managed space allocation are eliminated

To create a locally managed tablespace give the following command

SQL> CREATE TABLESPACE ica_lmts DATAFILE '/u02/oracle/ica/ica01.dbf' 

SIZE 50M EXTENT MANAGEMENT LOCAL AUTOALLOCATE;

AUTOALLOCATE causes the tablespace to be system managed with a minimum extent size of 64K.

The alternative to AUTOALLOCATE is UNIFORM. which specifies that the tablespace is managed with extents of uniform size. You can specify that size in the SIZE clause of UNIFORM. If you omit SIZE, then the default size is 1M. The following example creates a Locally managed tablespace with uniform extent size of 256K

SQL> CREATE TABLESPACE ica_lmt DATAFILE '/u02/oracle/ica/ica01.dbf' SIZE

 50M EXTENT MANAGEMENT LOCAL UNIFORM SIZE 256K;

To Create Dictionary Managed Tablespace

SQL> CREATE TABLESPACE ica_lmt DATAFILE '/u02/oracle/ica/ica01.dbf' SIZE

 50M EXTENT MANAGEMENT DICTIONARY;

Bigfile Tablespaces (Introduced in Oracle Ver. 10g)

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. Bigfile tablespaces can reduce the number of datafiles needed for a database.

To create a bigfile tablespace give the following command

SQL> CREATE BIGFILE TABLESPACE ica_bigtbs  DATAFILE '/u02/oracle/ica/big

tbs01.dbf' SIZE 50G;