Which two are true about instance recovery? (Choose two.)
Which two are true about instance recovery? (Choose two.)
Instance recovery in Oracle is automatically performed by the database when it is opened after a crash. This ensures that the database returns to a consistent state. During recovery, the necessary blocks are reconstructed so they become available as needed, although they are initially inaccessible until recovery is completed. FAST_START_MTTR_TARGET is a parameter that influences the duration of instance recovery. Setting it to a lower value reduces the time needed for recovery by prompting the system to write dirty buffers to disk more frequently, thereby minimizing the number of I/Os required during the recovery process.
CF are my choices
BC Instance recovey occurs when ALTER DATABASE OPEN not before.
well i'm not so sure about it: You are right about the instance recovery begins after "alter database open" is executed but that doesn't mean that the database is already open when the recovery starts. The instance recovery is executed in 2 steps, rollforward and rollback and the database is open just after the rollforward is completed. So i think that is not accuracy to tell that the instance recovery is performed after the database is open. What do you thik? Here is a good diagram to understand it. https://www.orskl.com/how-oracle-database-does-instance-recovery-after-failures/
Thanks you are correct ;)
c,f is ok
CF for me
C and F, no doubt.
BC is correct. wow. most of you are wrong. instance must be open to get undo segment online. without that, oracle doesn't know the undo data to recover the (not commited) transactions. so the phrase "remains in MOUNT state" is definitively wrong.
For me F is totally wrong. As others said the Instance recovery is performed in 2 steps , the first one is the rolling forward that needs Online Redo Logs to execute. Online Redo Logs are available just after database id open because in Mount state just control files are opened. So for me Correct answers are B & C
if you are saying redo is applied after DB open, you got your basics very wrong.
I also agree with BC and your explanation
I will choose c and F
C F, as most agrees
Answer is CF: F: instance recovery happens at mount state. from the student guide = ... The instance mounts the control files and then ATTEMPTS to open the datafiles. when it realizes the datafiles have not been synchronized during shutdown ..... B would have been correct if the word STARTED was used instead of OPENED.
BC is absolutely right see below https://docs.oracle.com/cd/A57673_01/DOC/server/doc/SPS73/chap23.htm
This is quite a poorly formed question in my mind, instance recovery starts when you 'startup' the database, not when it opens. If you run a shutdown abort you can clearly see in the alert log that the application of redo logs starts when the database is mounted after running the startup command and then the database is opened after it confirms that the undo tablespace is available. Then the undo is applied to rollback the database to a consistent state it was in before the unclean shutdown. So C is definitely true but B and F are both technically false as they ignore that Instance Recovery has two phases. Not sure if the Q is wrong on here but I would say that F is more true as IR starts when the DB is mounted, but it opens when rollforward is done, not when IR is completed.
CF,I Thinz
Oracle Database performs instance recovery automatically in the following situations: The database opens for the first time after the failure of a single-instance database or all instances of an Oracle RAC database. This form of instance recovery is also called crash recovery. Oracle Database recovers the online redo threads of the terminated instances together. https://docs.oracle.com/en/database/oracle/oracle-database/19/cncpt/oracle-database-instance.html#GUID-6F20EBD4-CD7A-41BA-823B-BB3B25C7C99E According to the documentation, B and C are true
i'm sure of CF
It think it was release 8 when the faster start was introduced by opening the instance BEFORE the recovery is complete. However, the recovered blocks remain unavailable until the recovery is done.
For me it's BC. https://docs.oracle.com/cd/E25178_01/server.1111/e25789/startup.htm Oracle Database performs instance recovery automatically in the following situations: The database opens for the first time after the failure of a single-instance database or all instances of an Oracle RAC database.