Oracle Active Data Guard has realtime query. Real time query means your physical standby database to be open read-only while Redo data is coming and apply active.

For example You change PROD database

select salary from employees where employee_id=100;

24000

then you change

update employees set salary=10000 where employee_id=100;

commit;

Up-to-date Meantime connect Physical database

select salary from employees where employee_id=100;

10000;

User connected to a physical standby database can query data that is up-to-date with the primary database.

First you must stop redo data applyfor open phy.standby in read only

DGMGRL>edit database orclstby set state=’apply-off’;

then open database

alter database open;

and last restart redo apply

Dgmgrl>edit database orclstby set state=’apply-on’;