You can use the transport tablespace from backup feature to transport tablespaces at a point in time without marking the source tablespaces READ ONLY.

This removes the need to set the tablespace set in READ ONLY mode while exporting its metadata which results in a period of unavailability.

The RMAN command TRANSPORT TABLESPACE is used to generate one version of a tablespace set. A tablespace set version comprises the following:

• The set of data files representing the tablespace set recovered to a particular point in   time.

• The Data Pump export dump files generated while doing a transportable tablespace   export of the recovered tablespace set

• The generated SQL script used to import the recovered tablespace set metadata into the   target database. This script gives you two possibilities to import the tablespace set   metadata into the target database: IMPDP or the   DBMS_STREAMS_TABLESPACE_ADM.ATTACH_TABLESPACES procedure.

Note: this option is time-consuming compared to the method that requires setting the tablespace in READ ONLY mode.

Following are the steps done by RMAN to implement the transport tablespace from backup:

1. While executing the TRANSPORT TABLESPACE command, RMAN starts an     auxiliary database instance on the same machine as the source database. The auxiliary     instance is started with a SHARED_POOL_SIZE set to 110 MB to accommodate the     Data Pump needs.

2. RMAN then restores the auxiliary set as well as the recovery set by using existing     backups. The restore operation is done to a point before the intended point in time of     the tablespace set version.

3. RMAN recovers the auxiliary database to the specified point in time.

4. At that point, the auxiliary database is open with the RESETLOGS option, and EXPDP     is used in TRANSPORTABLE TABLESPACE mode to generate the dump file set     containing the recovered tablespace set metadata.

5. RMAN then generates the import script file that can be used to plug the tablespace set     into your target database.

Note: The tablespace set may be kept online and in READ WRITE mode at the source database during the cloning process.

DUMP FILE - specifies the name of the generated Data Pump export dump file. Its default value is dmpfile.dmp

EXPORT LOG - specifies the name of the log file for the Data Pump export job. Its default value is explog.log

IMPORT SCRIPT - specifies the name of the sample import script. Its default value is impscrpt.sql. The import script is written to the location specified by the TABLESPACE DESTINATION parameter.

TABLESPACE DESTINATION - it is a required parameter that specifies the default location for the data files in the recovery set.

UNTIL - The UNTIL clause is used to specify the point-in-time for the tablespace set version. You may specify the point-in-time as an SCN, TIME, or log SEQUENCE.

In Oracle Database 10g Release 2, you can build a repository to store versions of tablespace, referred to as  tablespace rack. The repository may be located in the same database as the tablespaces being versioned, or may be located in a different database. Handling this option is not covered in this document.