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Which three statements are true about standby redo logs in a Data Guard configuration with no Oracle
Streams or Goldengate configured?

A.
They are required on a logical standby for real-time apply.

B.
They are required only for synchronous redo transport.

C.
Only standby databases can write redo to them.

D.
It is recommended to have them on the primary database.

E.
They are required on a physical standby for real-time apply.

F.
The LGWR process writes to them on a standby database.

Explanation:
A: SQL Apply converts the data from the archived redo log or standby redo log in to SQL statements and then
executes these SQL statements on the logical standby database.
Note: Log apply services use the following methods to maintain physical and logical standby databases:
* Redo apply (physical standby databases only)* SQL Apply (logical standby databases only)
E: Standby redo log files are required to use real-time apply.
By default, the redo data is applied from archived redo log files. When performing Redo Apply, a physical
standby database can use the real-time apply feature to apply redo directly from the standby redo log files as
they are being written by the RFS process.
Applying Redo Data to Physical Standby Databases
C: The archiver (ARCn) process or the log writer (LGWR) process on the primary database can transmit redo
data directly to remote standby redo log files, potentially eliminating the need to register a partial archived log
file (for example, to recover after a standby database crashes).
Incorrect Answers:
B: A: Standby redo log files are required to use real-time apply.
D: Standby redo log files are access by the Standby Database, not the primary database.
F: By default, the redo data is applied from archived redo log files. When performing Redo Apply, a physical
standby database can use the real-time apply feature to apply redo directly from the standby redo log files as
they are being written by the RFS process, (ot the LGWR process).
Ref: https://docs.oracle.com/cd/B19306_01/server.102/b14239/log_apply.htm

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