- logical backup [using export utility] works as an alternative backup method.
- The beauty of export is we can be selective [either at export or at import]
- We can export from one user and import into another within the same database
- We can export from one database and import into another database [both source and target databases are ORACLE datgabases]
- When migrating from one platfarm to another from WINDOWS to SUN SOLARIS then export is the only method to transfer the data [at least up on till 9i] since C/R/D files from the source can not be copied over to the target as file system are different types.
- WINDOWS PLATFORM SUN SOLARIS PLATE
- When upgrading ORACLE software, as a precaution, we can export of full database before the upgrade. If the upgrade utility able to successfully upgrade software as well as the database then its o.k., but Incase if software upgrading is successful where as data base up gradation has failed then we can still use the exported file which we did before the up gradation, so that we can bring back all the data.
- Over a period of time [3 to 4 months] as the data based 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 table spaces
- Import full data
The dump file is 8 to 10 times smaller than database even though we did full export. The reasons are
- No base tables are exported into target database.
- No control or redo log files rare exported into the target database.
- No temp table space is exported
- No undo segments since they contain before image.
- From user-index only definitions are exported but not the data.
- Original data 10 gbTables are exported with data but they may have 50% free blocks and also 70% pot free
Really used data 2.7 gb [ 10% pot free]Use data 3 gb [ 50% of occupied]
Occupied data 6 gb
[uses undo+ lots of log switches
imports takes 6 to 8 times than exports]
advantages of exports
- works for an alternative backup solutions.
- Selective exports or imports are possible
- Can copy objects
- One user to another user
- From one database to another database
- From one OS to another OS export files are platform independent.
- From one version to another version
- Database reorganization [ every 3 to 4 months]
- ORACLE up gradation