A Full System Export and Import is a useful way to replicate or clean up a database. Please note the following guidelines when performing a Full System Export and Import:
1. When performing the import, ensure you are pointing at the correct instance. Always check values for the SID and two task driver before proceeding.
*Note: On Unix systems, just entering a sub-shell, such as using C-shell, can change the database that the import would work against.
2. When possible, it is advisable to take a physical copy of the exported database and the database you intend to import into before starting the import. This ensures any mistakes are reversible.3. *NEVER* run a FULL SYSTEM IMPORT on a machine that has more than one database UNLESS you are 100% sure all tablespaces have been pre-created. A full import will create any undefined tablespaces using the same datafile names as the exported database. There are situations where this is very dangerous:-> If the datafiles belong to ANY other database, they will be CORRUPTED. This is especially true if the exported database is on the same machine, because its datafiles will be re-used by the database you are importing into.-> If the datafiles have names that clash with existing operating system files.
4. When exporting, it is advisable to also produce a report showing information you may need before / after the import:
-> List the tablespaces and datafiles
-> List the rollback segments (in case of using Manual Undo Management)
-> List a count, by user, of each object type such as tables, indexes, etc.
This enables you to ensure that tablespaces have been pre-created and to check the success of the import after it is complete.
5. If you are creating a completely new database from an export and you are using Manual Undo Management, remember to create an extra rollback segment in SYSTEM, and make this available in the init.ora file before proceeding with the import.
6. There are some versions of export that do not retain sequence numbers correctly. It is advisable to select next_value for each sequence after the export so that these can be checked after import.
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