What is Standby snapshot Database?
Oracle provides an unique feature where the physical standby database can be opened in READ WRITE mode to perform update able transactions.
A snapshot standby database is a fully updatable standby database that is created by converting a physical standby database into a snapshot standby database. A snapshot standby database
receives and archives, but does not apply redo data from a primary database. Redo data received from the primary database is applied when a snapshot standby database is converted back
into a physical standby database, after discarding all local updates to the snapshot standby database.
A snapshot standby database typically diverges from its primary database over time because redo data from the primary database is not applied as it is received. Local updates to the
snapshot standby database will cause additional divergence. The data in the primary database is fully protected however, because a snapshot standby can be converted back into a
physical standby database at any time, and the redo data received from the primary will then be applied.
A snapshot standby database will allow you to make use of the data available on the physical standby database (which is the same data of the primary database), which allows the users
to test the application on a standby database which has the primary database's data before implementing it into production environment. Whenever a physical standby database is converted
into a snapshot standby database, a guaranteed restore point is automatically created. Once when the updateable transactions are completed for testing purposes on the snapshot standby
database and when you are converting back the snapshot standby to physical standby, oracle flashbacks to the restore point that was created earlier which means the transactions
which were made in standby database while it was open in READ WRITE mode will be flushed out.
The only requirement to have the snapshot standby is that FRA (Flash Recovery Area) must be configured on physical standby database. It is not necessary to have flashback enabled.
