Making User-Managed Backups of Online Tablespaces and Datafiles

You can back up all or only specific datafiles of an online tablespace while the database is open. The procedure differs depending on whether the online tablespace is read/write or read-only.

Note:

You should not back up temporary tablespaces.

Making User-Managed Backups of Online Read/Write Tablespaces

You must put a read/write tablespace in backup mode to make user-managed datafile backups when the tablespace is online and the database is open. The ALTER TABLESPACE ... BEGIN BACKUP statement places a tablespace in backup mode. In backup mode, the database copies whole changed data blocks into the redo stream. After you take the tablespace out of backup mode with the ALTER TABLESPACE ... END BACKUP or ALTER DATABASE END BACKUP statement, the database advances the datafile header to the current database checkpoint.

When restoring a datafile backed up in this way, the database asks for the appropriate set of redo log files to apply if recovery be needed. The redo logs contain all changes required to recover the datafiles and make them consistent.

To back up online read/write tablespaces in an open database:

Before beginning a backup of a tablespace, identify all of the datafiles in the tablespace with the DBA_DATA_FILES data dictionary view. For example, assume that you want to back up the users tablespace. Enter the following:

SELECT TABLESPACE_NAME, FILE_NAME
FROM SYS.DBA_DATA_FILES
WHERE TABLESPACE_NAME = 'USERS';
 
TABLESPACE_NAME                   FILE_NAME
-------------------------------   --------------------
USERS                             /oracle/oradata/trgt/users01.dbf
USERS                             /oracle/oradata/trgt/users02.dbf

Mark the beginning of the online tablespace backup. For example, the following statement marks the start of an online backup for the tablespace users:

SQL> ALTER TABLESPACE users BEGIN BACKUP;

Caution:

If you do not use BEGIN BACKUP to mark the beginning of an online tablespace backup and wait for that statement to complete before starting your copies of online tablespaces, or then the datafile copies produced are not usable for subsequent recovery operations. Attempting to recover such a backup is risky and can return errors that result in inconsistent data. For example, the attempted recovery operation can issue a "fuzzy files" warning, and can lead to an inconsistent database that you cannot open.

Back up the online datafiles of the online tablespace with operating system commands. For example, UNIX users might enter:

% cp /oracle/oradata/trgt/users01.dbf /d2/users01_'date "+%m_%d_%y"'.dbf
% cp /oracle/oradata/trgt/users02.dbf /d2/users02_'date "+%m_%d_%y"'.dbf

After backing up the datafiles of the online tablespace, run the SQL statement ALTER TABLESPACE with the END BACKUP option. For example, the following statement ends the online backup of the tablespace users:
```
SQL> ALTER TABLESPACE users END BACKUP;
```

Archive the unarchived redo logs so that the redo required to recover the tablespace backup is archived. For example, enter:

SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;

Caution:

If you fail to take the tablespace out of backup mode, then Oracle continues to write copies of data blocks in this tablespace to the online logs, causing performance problems. Also, you will receive an ORA-01149 error if you try to shut down the database with the tablespaces still in backup mode.

Making Multiple User-Managed Backups of Online Read/Write Tablespaces

When backing up several online tablespaces, you can back them up either serially or in parallel. Use either of the following procedures depending on your needs.

Backing Up Online Tablespaces in Parallel

You can simultaneously create datafile copies of multiple tablespaces requiring backups in backup mode. Note, however, that by putting all tablespaces in online mode at once, you can generate large redo logs if there is heavy update activitiy on the affected tablespaces, because the redo must contain a copy of each changed data block in each changed datafile. Be sure to consider the size of the likely redo before using the procedure outlined here.

To back up online tablespaces in parallel:

Prepare all online tablespaces for backup by issuing all necessary ALTER TABLESPACE statements at once. For example, put tablespaces users, tools, and indx in backup mode as follows:
```
SQL> ALTER TABLESPACE users BEGIN BACKUP;
SQL> ALTER TABLESPACE tools BEGIN BACKUP;
SQL> ALTER TABLESPACE indx BEGIN BACKUP;
```
If you are backing up all tablespaces, you might want to use this command:
```
SQL> ALTER DATABASE BEGIN BACKUP;
```
Back up all files of the online tablespaces. For example, a UNIX user might back up datafiles with the *.dbf suffix as follows:
```
% cp $ORACLE_HOME/oradata/trgt/*.dbf /disk2/backup/
```
Take the tablespaces out of backup mode as in the following example:
```
SQL> ALTER TABLESPACE users END BACKUP;
SQL> ALTER TABLESPACE tools END BACKUP;
SQL> ALTER TABLESPACE indx END BACKUP;
```
Again, it you are handling all datafiles at once you can use the ALTER DATABASE command instead of ALTER TABLESPACE:
```
SQL> ALTER DATABASE END BACKUP;
```
Archive the online redo logs so that the redo required to recover the tablespace backups will be available for later media recovery. For example, enter:
```
SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;
```

Backing Up Online Tablespaces Serially

You can place all tablespaces requiring online backups in backup mode one at a time. Oracle recommends the serial backup option because it minimizes the time between ALTER TABLESPACE ... BEGIN/END BACKUP statements. During online backups, more redo information is generated for the tablespace because whole data blocks are copied into the redo log.

To back up online tablespaces serially:

Prepare a tablespace for online backup. For example, to put tablespace users in backup mode enter the following:
```
SQL> ALTER TABLESPACE users BEGIN BACKUP;
```
In this case you probably do not want to use ALTER DATABASE BEGIN BACKUP to put all tablespaces in backup mode simultaneously, because of the unnecessary volume of redo log information generated for tablespaces in online mode.

Back up the datafiles in the tablespace. For example, enter:

% cp /oracle/oradata/trgt/users01.dbf /d2/users01_'date "+%m_%d_%y"'.dbf

Take the tablespace out of backup mode. For example, enter:
```
SQL> ALTER TABLESPACE users END BACKUP;
```
Repeat this procedure for each remaining tablespace.
Archive the unarchived redo logs so that the redo required to recover the tablespace backups is archived. For example, enter:
```
SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;
```

Ending a Backup After an Instance Failure or SHUTDOWN ABORT

The following situations can cause a tablespace backup to fail and be incomplete:

The backup completed, but you did not run the ALTER TABLESPACE ... END BACKUP statement.
An instance failure or SHUTDOWN ABORT interrupted the backup.

Whenever crash recovery is required, if a datafile is in backup mode when an attempt is made to open it, then the database will not open the database until either a recovery command is issued, or the datafile is taken out of backup mode.

For example, the database may display a message such as the following at startup:

ORA-01113: file 12 needs media recovery
ORA-01110: data file 12: '/oracle/dbs/tbs_41.f'

If the database indicates that the datafiles for multiple tablespaces require media recovery because you forgot to end the online backups for these tablespaces, then so long as the database is mounted, running the ALTER DATABASE END BACKUP statement takes all the datafiles out of backup mode simultaneously.

In high availability situations, and in situations when no DBA is monitoring the database, the requirement for user intervention is intolerable. Hence, you can write a crash recovery script that does the following:

Mounts the database
Runs the ALTER DATABASE END BACKUP statement
Runs ALTER DATABASE OPEN, allowing the system to come up automatically

An automated crash recovery script containing ALTER DATABASE END BACKUP is especially useful in the following situations:

All nodes in an Oracle Real Application Clusters (RAC) configuration fail.
One node fails in a cold failover cluster (that is, a cluster that is not a RAC configuration in which the secondary node must mount and recover the database when the first node fails).

Alternatively, you can take the following manual measures after the system fails with tablespaces in backup mode:

Recover the database and avoid issuing END BACKUP statements altogether.
Mount the database, then run ALTER TABLESPACE ... END BACKUP for each tablespace still in backup mode.

Ending Backup Mode with the ALTER DATABASE END BACKUP Statement

You can run the ALTER DATABASE END BACKUP statement when you have multiple tablespaces still in backup mode. The primary purpose of this command is to allow a crash recovery script to restart a failed system without DBA intervention. You can also perform the following procedure manually.

To take tablespaces out of backup mode simultaneously:

Mount but do not open the database. For example, enter:
```
SQL> STARTUP MOUNT
```

If performing this procedure manually (that is, not as part of a crash recovery script), query the V$BACKUP view to list the datafiles of the tablespaces that were being backed up before the database was restarted:

SQL>  SELECT * FROM V$BACKUP WHERE STATUS = 'ACTIVE';
FILE#      STATUS             CHANGE#    TIME     
---------- ------------------ ---------- ---------
        12 ACTIVE                  20863 25-NOV-02
        13 ACTIVE                  20863 25-NOV-02
        20 ACTIVE                  20863 25-NOV-02
 3 rows selected.

Issue the ALTER DATABASE END BACKUP statement to take all datafiles currently in backup mode out of backup mode. For example, enter:
```
SQL> ALTER DATABASE END BACKUP;
```
You can use this statement only when the database is mounted but not open. If the database is open, use ALTER TABLESPACE ... END BACKUP or ALTER DATABASE DATAFILE ... END BACKUP for each affected tablespace or datafile.

Caution:

Do not use ALTER DATABASE END BACKUP if you have restored any of the affected files from a backup.

Ending Backup Mode with the SQL*Plus RECOVER Command

The ALTER DATABASE END BACKUP statement is not the only way to respond to a failed online backup: you can also run the SQL*Plus RECOVER command. This method is useful when you are not sure whether someone has restored a backup, because if someone has indeed restored a backup, then the RECOVER command brings the backup up to date. Only run the ALTER DATABASE END BACKUP or ALTER TABLESPACE ... END BACKUP statement if you are sure that the files are current.

Note:

The RECOVER command method is slow because the database must scan redo generated from the beginning of the online backup.

To take tablespaces out of backup mode with the RECOVER command:

Mount the database. For example, enter:
```
SQL> STARTUP MOUNT
```
Recover the database as normal. For example, enter:
```
SQL> RECOVER DATABASE
```
Use the V$BACKUP view to confirm that there are no active datafiles:
```
SQL>  SELECT * FROM V$BACKUP WHERE STATUS = 'ACTIVE';
FILE#      STATUS             CHANGE#    TIME     
---------- ------------------ ---------- ---------
0 rows selected.
```
See Also:
Chapter 18, "Performing User-Managed Database Flashback and Recovery" for information on recovering a database

Making User-Managed Backups of Read-Only Tablespaces

When backing up an online read-only tablespace, you can simply back up the online datafiles. You do not have to place the tablespace in backup mode because the database is not permitting changes to the datafiles.

If the set of read-only tablespaces is self-contained, then in addition to backing up the tablespaces with operating system commands, you can also export the tablespace metadata with the transportable tablespace functionality. In the event of a media error or a user error (such as accidentally dropping a table in the read-only tablespace), you can transport the tablespace back into the database.