What is the difference between real-time apply and real-time query?

Real-time apply is the process of applying the redo in the current standby redo log file as it is being filled, in contrast to waiting for the standby redo log to be filled up. By default, apply services will wait for a standby redo log file to be archived, then apply the redo that it contains.


Real-time query is the process of applying redo redo while the physical standby database is open
This allows for read-only usage of the data which is identical to the primary database.
Note: Real-time query is licenced as the "Active Data Guard" option.


Real-time apply is documented here

Real-time query is documented here