Logical Backup

 

1.Logical backup [using export utility] works as an alternative backup method

2.The beauty of export is we can be selective [either at export or at import ]

3.We can export from one user and import into another within the same database.

4.We can export from one database and import into another database [both source and target databases are oracle databases] 

5.Weh  migrating from one platform to another from WINDOWS to SUN SOLARIS then export is the only method to transfer the datab[ at least upon till 9i] since C/R/D files from the source can not be copied over to the target as file systems are different types

6. When Upgrading Oracle software, as a precaution, we can take an export of the full database before the upgrade

if the upgrade utility is able to successfully upgrade software as well as the database then it's ok, but

incase software upgrading is successful whereas database upgradation has failed then we can still use the exported file which we did before the upgradation, so that we can bring back all the data.

7. Over a period of time [3 to 4 months ] as the database get fragmentation, being a DBA we used to go for REORG which includes

•  export full database
•  drop the existing database
•  recreate an empty database with all the required tablespaces
•  import full data

The dump file is 8 to 10 times smaller than  the database even though we did full export 

The reasons are

1. no base tables are exported into the target database

2. no control or redo log files are exported into the target database

3. no temp tablespace is exported

4. no undo segments since they contain before image

5.from user-index the only definition is exported but not the data

6.tables are exported with data but they may have 90 % free blocks and also 10% pctfree

  Original data---- 10GB

  Occupied data ----- 6GB

  Used data     -------3GB [ 50% of Occupied ]

  reality used data ----2.7GB [ 10% pctfree]

Advantages of exports:

1. Works for alternative  backup solutions

2. Selective exports or imports are possible

3. Can copy objects 

•    One user to another user
•    from one database to another database 
•    from one OS to another OS as export files are platform-independent
•    from one version to another version

4. Database reorganization [every 3 to 4 months ]

5. ORACLE upgradation