3.7 Introduction to backup and recovery mechanism
            ---------------------------------------------

- physical and logical backup/recovery

3.7.1 Physical backup/recovery
      ------------------------

- Archive log mode. Types of failures (user, statement, user
  process, instance (automatic), media).

- Physical backup methods: offline (cold), online (hot). Full and
  partial backups.

  - Online backup

    See PH95p#164,v2 by Rama Velpury
    For releases >= 7.2 a new functionalitity is introduced:
    if the machine crashed while taking HOT (ONLINE) backup the
    headers of the files of tablespaces which where in BEGIN
    BACKUP mode are not updated during checkpointing and have the
    old log sequence number. Any attempt to startup database
    causes "ORA-01113: file n needs media recovery" error.
    To fix thei problem v7.2 introduces new command:
     ALTER DATABASE DATAFILE 'file_name' END BACKUP;
    which writes in the file header valid log sequence number.

    Oracle can distinguish between a current data file in HOT
    BACKUP MODE and a RESTORED COPY of the data file by compiring
    the CHECKPOINT COUNTERS in the file header and the control
    file.

    V$BACKUP view allows check to see whether any data files are
        in HOT BACKUP mode. If the Status column says ACTIVE,
        then the file is in HOT BACKUP mode

- Recovery without achieving. Recovery steps.

- Partial recovery (until cancel, time, SCN)

  WARNING! After restoring all the files (database, control, redo
           logs) DO NOT STARTUP OPEN restored database because
           status on files is changed and subsequent recovery will
           fail!
           You must STARTUP MOUNT and
                    RESTORE DATABASE UNTIL <...> [USING
                      BACKUP CONTROL FILE]

- Structures required for recovery.

- Operate with achieving.

- Archive modes overview.

- Display archive status.

- Specify and change archive modes.

- Enable and disable archive processing.

- Online partial database backup.

- Offline partial tablespace backup.

- Recover all transactions after media failure. Recover online
  redo log and control file.

- Incomplete (partial) recovery.

3.7.2 Logical backup/recovery & space compaction
      ------------------------------------------

- export/import.

- Export modes. Possible exports scenarios.

- Import modes.

- Questions and answers

  Q: What should you be aware of with a full import from one
     database to another?? Is it different if Oracle7?

  A: Be aware of export/import from one database into another on
     the same machine when running V6. You should be very
     careful, and pre-create all of the tablespaces with the same
     name regardless of whether you want them  or not. With a
     full import all the tablespaces are created and with the
     datafiles reused. The export file has the exact path to the
     datafiles. For example, although I am importing from my test
     database into my production, tablespaces will be
     initialized.  The production database will crash at the next
     file access, and the only way to recover is to go to a
     backup.

     This is how the create tablespace statement books in import:

      . importing user SYSTEM
        "CREATE TABLESPACE "TEST" DATAFILE
        'DISK$TEMP:[VMSSPT.VMSSPT1.DB_VMSSPT3]TES"
         "T.DBS' SIZE 2097152 REUSE DEFAULT STORAGE (INITIAL
         10240 NEXT 10240 MINEXTENTS 1 MAXEXTENS 99 PCTINCREASE
         50) ONLINE"

      A possible workaround is to rename the dbs files of all you
      tablespaces, precreate ALL the tablespaces, or don't issue
      a full import.

      Its natural to think, sure all you have to do is export from one and
      import into another, however, this could cause problems.

      This doesn't apply to the Oracle7 import utility, it has
      the DESTROY option added for this issue. DESTROY=N tells
      import that if the file exists, do not destroy it, instead,
      give an error on the create tablespaces statement.
      DESTROY=Y will reuse the tablespace file.