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
A,C,E
Use the ALTER DATABASE statement to enable the real-time apply feature, as follows:
• For physical standby databases, issue the ALTER DATABASE RECOVER MANAGED STANDBY DATABASE statement. (As of Oracle Database 12c Release 1 (12.1), the USING CURRENT LOGFILE clause is deprecated and no longer necessary to start real-time apply.)
• For logical standby databases, issue the ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE statement. Real-time apply requires a standby database that is configured with a standby redo log and that is in ARCHIVELOG mode.
Figure shows an Oracle Data Guard configuration with a local destination and a standby destination. As the remote file server (RFS) process writes the redo data to standby redo log files on the standby database, apply services can recover redo from standby redo log files as they are being filled.
Wrong Answers:
B: They are not only used for Synchronous Redo Transport.
Standby redo logs are required to implement:
• Synchronous transport mode
• Real-time apply
• Cascaded redo log destinations
I think it should be D instead of C so correct Ans: A,D,E
Though the Standby logs are on the Standby side it is not written by Standby database. Remote File Server (RFS) process write to them. It is recommended to have the standby logs on the Primary for successful switchover and failover operations.
https://docs.oracle.com/database/121/SBYDB/log_apply.htm#GUID-9922F0E7-3E19-449E-8C35-57B7E5714C54__I1021537
You are right chunn : A,D,E
C is wrong because it is the primary that writes redo to them using the LNS and RFS processes.It is the RFS process on the standby server that writes to them , not the database itself.The standby database only reads them to apply the redo.
A,D,E