You are in the middle of a transaction and very crucial data has been modified. Because of a
hardware failure, the instance has shut down before synchronizing all the database files. Which two
statements are true? (Choose two.)
A.
On startup, SMON coordinates instance recovery.
B.
On startup, CKPT coordinates instance recovery.
C.
On startup, use RMAN to perform instance recovery.
D.
Uncommitted changes will be rolled back after the database is opened.
E.
On startup, perform media recovery and then instance recovery.
F.
On startup, all the files will be synchronized and you get both committed and uncommitted data.
After an instance crash, you start up the database by issuing the STARTUP
command. Instance recovery is initiated by the SMON background process.
The information used for instance recovery will be derived from the control file.
The uncommitted changes are rolled back using information in the undo segments.
The committed and uncommitted changes stored in the online redo log are applied to the
affected data blocks.
The recovery is triggered by smon comparing thre control files and data file headers. If the stop scn of the datafile doesn’t match with the checkpoint scn of control file, recovery is triggered.
The process of the instance recovery is
If the Oracle instance fails any information in the SGA that is not been written back to disk is lost. For eg, the failure of the OS causes an instance failure. After the loss of the instance, the BG Process SMON automatically performs instance recovery when the database is reopened.
It will go through the following process.
1) ROLL FORWARD Phase:
Rolling forward to recover data that has not been recorded in the data files but that has been recorded in the online redo log. This data has not been written to disk because of the loss of the SGA during instance failure. During this process, SMON reads the redo log files and applies the changes recorded in the redo log to the data blocks. Because we have all committed and uncommited transactions in the redo log files, this process recovers the transactions.
2) OPEN the DATABASE:
Opens the database for user access so that users can log on to the database and do their operations and key thing here is data that is not locked by unrecovered transactions is available immediatly.
3) ROLLBACK Phase:
as name itself clearly depicts, rollback the uncommited transactions.
During startup,SMON performs instance recovery.
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