In very rare situations, you might need to bring specific datafiles online (make them available) or take specific files offline (make them unavailable). For example, when Oracle7 has problems writing to a datafile, it can automatically take the datafile offline. You might need to take the damaged datafile offline or bring it online manually.
Note: You can make all datafiles in a tablespace, other than the files in the SYSTEM tablespace, temporarily unavailable by taking the tablespace offline. You must leave these files in the tablespace to bring the tablespace back online.
Offline datafiles cannot be accessed. Bringing a datafile in a read-only tablespace online makes the file readable. No one can write to the file unless its associated tablespace is returned to the read-write state. The files of a read-only tablespace can independently be taken online or offline using the DATAFILE option of the ALTER DATABASE command.
To bring a datafile online or take it offline, in either archiving mode, you must have the ALTER DATABASE system privilege. You can perform these operations only when the database is open in exclusive mode.
Note: To use this option of the ALTER DATABASE command, the database must be in ARCHIVELOG mode. This requirement prevents you from accidentally losing the datafile, since taking the datafile offline while in NOARCHIVELOG mode is likely to result in losing the file.
The following statement brings the specified datafile online:
ALTER DATABASE DATAFILE 'filename' ONLINE;
See Also: For more information about bringing datafiles online during media recovery, see ![[*]](jump.gif)
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The following statement brings the specified datafile offline:
ALTER DATABASE DATAFILE 'filename' OFFLINE DROP;