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.
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