Which two statements are true about Real-Time Query?
A.
Setting STANDBY_MAX_DATA_DELAY =0 requires synchronous redo transport.
B.
Disabling Real-Time Query prevents the automatic start of redo apply when a physical standby database is opened READ ONLY.
C.
Real-Time Query sessions can be connected to a Far Sync instance.
D.
Real-Time Query has no limitations regarding the protection level of the Data Guard environment.
E.
A standby database enabled for Real-Time Query cannot be the Fast-Start Failover target of the Data Guard configuration.
Explanation:
If a license for the Oracle Active Data Guard option has been purchased, Redo Apply can be active while the physical standby database is open, thus allowing
queries to return results that are identical to what would be returned from the primary database. This capability is known as the real-time query feature.
Incorrect Answers:
A: If STANDBY_MAX_DATA_DELAY is set to 0, a query issued to a physical standby database is guaranteed to return the exact same result as if the query were
issued on the primary database, unless the standby database is lagging behind the primary database, in which case an ORA-3172 error is returned.
Note: The STANDBY_MAX_DATA_DELAY session parameter can be used to specify a session-specific apply lag tolerance, measured in seconds, for queries
issued by non-administrative users to a physical standby database that is in real-time query mode. This capability allows queries to be safely offloaded from the
primary database to a physical standby database, because it is possible to detect if the standby database has become unacceptably stale.
C is doubtful. There is no documented way to turn off RTQ (apart from just not opening the DB). I would favour A. If STANDBY_MAX_DATA_DELAY is 0 and transport is not SYNC, you should ALWAYS get ORA-3172, which kind of breaks the RTQ feature entirely.
Correct: A,D
The following additional restrictions apply if STANDBY_MAX_DATA_DELAY is set to 0 or if the ALTER SESSION SYNC WITH PRIMARY SQL statement is used:
The standby database must receive redo data via the SYNC transport.
The redo transport status at the standby database must be SYNCHRONIZED and the primary database must be running in either maximum protection mode or maximum availability mode.
Real-time apply must be enabled.
The COMPATIBLE database initialization parameter must be set to 11.0 or higher to use the real-time query feature of the Oracle Active Data Guard option.
A, B, D
B can be accomplished with an undocumentend parameter _query_on_phyiscal
As it is undocumented, i would prefer A, D
I think that:
D – This is wrong! They can be in “maximum availabilty” or “maximum protection” mode and cannot be in “maximum performance” mode. Maximum performance mode requirement: Set the ASYNC and NOAFFIRN redo transport attributes of the LOG ARCHIVE DEST n parameter on at least one standby database. Redo data is shipped to the standby database asynchronously with respect to the commitment of the transactions that create the redo data.
What do you think about it?
Configuring Zero Lag Betvveen the Primary and Standby Databases
• Certain applications have zero tolerance for any lag.
• A query on the standby database must return the same result as if it were executed on the primary database.
• Enforce by setting STANDBY MAX DATA DELAY to 0.
• The standby database must have advanced to a value equal to that of the current SON on the primary database at the time the query was issued.
• Results are guaranteed to be the same as the primary database; otherwise, an ORA-3 172 error is returned.
. The primary database must operate in maximum availability or maximum protection mode.
. SYNC must be specified for redo transport.
• Real-time query must be enabled.
Enabling Real-TIme Query Apply
A physical standby database instance cannot be opened if Redo Apply is active on a mounted instance of that database. In order to enable real-time query:
• Stop the Redo Apply process
• Open the database for read-only access
• Restart the Redo Apply with the real-time option that is now the default mode for Oracle Database 12c Release 1.
The COMPATIBLE database initialization parameter must be set to 11 .0 or higher to use the real-time query feature of the Oracle Active Data Guard option.
Note: When using the Oracle Data Guard broker, it is not necessary to stop Redo Apply and restart Redo Apply when enabling real-time query. Real-time query is not the same as real time apply, which was covered in the previous lesson. Real-time apply allows the recovery mechanisms to read from the standby redo logs at the same time that redo is being written to the standby redo logs. In the normal physical standby mode of operation, the database is only at the mount mode and would not allow any queries against user tables, even though real time apply is enabled. Real-time query with Oracle Active Data Guard extends real-time apply by allowing the database to be opened and queries performed against it.
A – This is correct!
B – This is not true! If a license for the Oracle Active Data Guard option has been purchased, a physical standby database can be open while Redo Apply is active. And i can operate my physical standby database without “Real-Time Queries” configured.
C – This is wrong! This is not possible! You cannot connect with a Far Sync instance; they are used only for ships the redo log information to a remote sites
D – This is wrong! They can be in “maximum availabilty” or “maximum protection” mode and cannot be in “maximum performance” mode. Maximum performance mode requirement: Set the ASYNC and NOAFFIRN redo transport attributes of the LOG ARCHIVE DEST n parameter on at least one standby database. Redo data is shipped to the standby database asynchronously with respect to the commitment of the transactions that create the redo data.
E – ?
A, D
I think is A and B
A – It’s correct
B – Correct – You open the standby database in Read Only and if RTA is not actived, it doesnt apply any redo.
D- Incorrect – Real-Time Query HAS limitations when the mode is MAX Performance. It could lag from primary.