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Explain Snap Shot StandBy database and the use of it

Explain Snap Shot StandBy database and the use of it?

Able to open standby database in read-write. This is very useful to turn our standby database into application testing / development purposes. This is achieved through snapshot standby database.

In order to create snapshot standby database:

1. Standby database must be a physical standby database
2. Flashback logging must be enabled on both primary and standby database
3. After enabling flashback mode, connect to dgmgrl utility in the primary database:
4. DGMGRL> CONVERT DATABASE STDBY TO SNAPSHOT STANDBY;
SQL> alter database convert to snapshot standby;

NOTE: Snap Shot StandBy – Is recommended if we have more than one standby database to the primary database.
From now on, we can do any testing (like creating new schemas, tables and so on) on our standby database. Please note that at this point of time; all the redo generated in our production database will be still shipped to standby database. 
But it is just that not going to be applied until the database is converted into physical standby mode.

5. Once the testing done, you can convert the snapshot standby database to physical standby with just 1 command:
DGMGRL>CONVERT DATABASE STDBY TO  PHYSICAL STANDBY;
6. Note that when the above command executed
All the changed made to the snapshot standby database (such as creating new schemas, tables) has been terminated
Previous physical standby database state is initiated
Physical standby database is mounted and MRP process is initiated. MRP will apply all the logs which was shipped yet applied during the snapshot standby database state.
7. Duration for this process is depends on few factors:
The amount of changes made to the database during the snapshot standby database state. More changes will lead to more time to rewind the changes via flashback database option.
The amount of archived logs generated during the snapshot standby database state. More archive logs will cause more time to apply it when the database is converted to physical standby database.
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