Backing up an Oracle database while the database instance is running is a hot backup. If you plan to perform a hot backup, you must operate your database in ARCHIVELOG mode.
Enter the ALTER TABLESPACE > BEGIN BACKUP command prior to the backup of each tablespace; this tells Oracle that a hot backup is being performed. If this command is not issued, the hot backup appears to succeed but may be useless for restoring the database. To finish the hot backup, for each tablespace, enter the ALTER TABLESPACE > END BACKUP command.
Changes to data are recorded and held in the rollback segment until they are no longer needed by any outstanding transaction. Taking a hot backup prevents the release of rollback segment data until the ALTER TABLESPACE … END BACKUP command is issued. Therefore, the rollback segment must be large enough to accommodate changes made during the hot backup. If the rollback segment runs out of space, a transaction will fail with an ORA-1555 error:
ORA-1555: snapshot too old (rollback segment too small)
While the hot backup succeeds despite this error, changes made to the database may need to be reentered.
You can avoid this error by performing a hot backup during times of low database activity or by ensuring that your rollback segments are large enough to accommodate data changes made during backup.
You do not need to shut down the ArcSDE server process (giomgr) prior to making a hot backup.
For details on hot backup, refer to the
Oracle Backup and Recovery Guide for your Oracle release.
Cold backup
Creating a backup of an Oracle database while the database instance is shut down is a cold backup. Managing a cold backup is simpler than a hot backup and less prone to error.
If you run the database in NOARCHIVELOG mode, a cold backup is your only option. Running the database in ARCHIVELOG mode enables you to use a cold backup to recover a database to the latest committed transaction.
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