Types of standby databases

1. Physical standby

• exactly block to block same as production database
• no queries allowed

2. Logical standby

• Its logically same as production db
• logs continue to apply in the background

3. Snapshot standby

• logs are received from primary but not applied until snapshot is converted back to physical stb

4. Active database guard

• Standby db will be in open mode
• normal user transactions can also continue on standby