You performed an incremental level 0 backup of a database:
RMAN > BACKUP INCREMENTAL LEVEL 0 DATABASE;
To enable block change tracking after the incremental level 0 backup, you issued this command:
SQL > ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE
‘ /mydir/rman_change_track.f’;
To perform an incremental level 1 cumulative backup, you issued this command:
RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE;
Which three statements are true?
A.
Backup change tracking will sometimes reduce I/O performed during cumulative incremental
backups.
B.
The change tracking file must always be backed up when you perform a full database backup.
C.
Block change tracking will always reduce I/O performed during cumulative incremental
backups.
D.
More than one database block may be read by an incremental backup for a change made to a
single block.
E.
The incremental level 1 backup that immediately follows the enabling of block change tracking
will not read the change tracking file to discover changed blocks.
Explanation:
Note:
* An incremental level 0 backup backs up all blocks that have ever been in use in this database.
* In a cumulative level 1 backup, RMAN backs up all the blocks used since the most recent level 0
incremental backup.
* Oracle Block Change Tracking
Once enabled; this new 10g feature records the modified since last backup and stores the log of itin a block change tracking file using the CTW (Change Tracking Writer) process. During backups
RMAN uses the log file to identify the specific blocks that must be backed up. This improves
RMAN’s performance as it does not have to scan whole datafiles to detect changed blocks.
Logging of changed blocks is performed by the CTRW process which is also responsible for
writing data to the block change tracking file.
NOT B. RMAN does not support backup and recovery of the change-tracking file itself
NOT C. Consider the eight-bitmap limit when developing your incremental backup strategy. For example, if you make a level 0 database backup followed by seven differential incremental backups, then the block change tracking file now includes eight bitmaps. If you then make a cumulative level 1 incremental backup, then RMAN cannot optimize the backup, because the bitmap corresponding to the parent level 0 backup is overwritten with the bitmap that tracks the current changes.
So ADE?
?????
B – FALSE – RMAN does not support backup and recovery of the change-tracking file itself true but qestion dont ask abouth RMAN backup of this file – this file is not backup becouse will be recreatet after backup full if dont exist
“…The database resets the change tracking file when it determines that the change tracking file is invalid…”
C – FALSE – not always reduce
“…if you make a level 0 database backup followed by seven differential incremental backups, then the block change tracking file now includes eight bitmaps. If you then make a cumulative level 1 incremental backup, then RMAN cannot optimize the backup, because the bitmap corresponding to the parent level 0 backup is overwritten with the bitmap that tracks the current changes….”
E – FLASE- first must be full backup before enabling change tracking
The first level 0 incremental backup scans the entire data file. Subsequent incremental backups use the block change tracking file to scan only the blocks that have been marked as changed since the last backup. An incremental backup can be optimized only when it is based on a parent backup that was made after the start of the oldest bitmap in the block change tracking file.
http://docs.oracle.com/database/121/BRADV/rcmbckba.htm#BRADV89535
BCE
B: It is not backed up according to section 4.4.4 of Backup and Recovery Basics:
http://docs.oracle.com/cd/B19306_01/backup.102/b14192/bkup004.htm#sthref418
B: you must do following during restore,recover DB due to oracle don’t backup tracking file.
restore database;
SQL ‘ALTER DATABASE DISABLE BLOCK CHANGE TRACKING’;
recover database;
Answer is ADE
B – False RMAN does not support backup and recovery of the change tracking file. The database resets the change tracking file when it determines that the change tracking file is invalid. If you restore and recover the whole database or a subset, then the database resets the block change tracking file and starts tracking changes again. After you make a level 0 incremental backup, the next incremental backup can use change tracking data.
C- False Consider the eight-bitmap limit when developing your incremental backup strategy. For example, if you make a level 0 database backup followed by seven differential incremental backups, then the block change tracking file now includes eight bitmaps. If you then make a cumulative level 1 incremental backup, then RMAN cannot optimize the backup, because the bitmap corresponding to the parent level 0 backup is overwritten with the bitmap that tracks the current changes.
ADE
RMAN’s change tracking feature for incremental backups improves incremental backup performance by recording changed blocks in each datafile in a change tracking file. If change tracking is enabled, RMAN uses the change tracking file to identify changed blocks for incremental backup, thus avoiding the need to scan every block in the datafile.
After enabling change tracking, the first level 0 incremental backup still has to scan the entire datafile, as the change tracking file does not yet reflect the status of the blocks. Subsequent incremental backup that use this level 0 as parent will take advantage of the change tracking file.
Using change tracking in no way changes the commands used to perform incremental backups, and the change tracking files themselves generally require little maintenance after initial configuration.
Change tracking is disabled by default, because it does introduce some minimal performance overhead on your database during normal operations. However, the benefits of avoiding full datafile scans during backup are considerable, especially if only a small percentage of data blocks are changed between backups. If your backup strategy involves incremental backups, then you should enable change tracking.
One change tracking file is created for the whole database. By default, the change tracking file is created as an Oracle managed file in DB_CREATE_FILE_DEST. You can also specify the name of the block change tracking file, placing it in any location you choose.
Although RMAN does not support backup and recovery of the change-tracking file itself, if the whole database or a subset needs to be restored and recovered, then recovery has no user-visible effect on change tracking. After the restore and recovery, the change tracking file is cleared, and starts recording block changes again. The next incremental backup after any recovery is able to use change-tracking data. B is incorrect.
After enabling change tracking, the first level 0 incremental backup still has to scan the entire datafile, as the change tracking file does not yet reflect the status of the blocks. Subsequent incremental backup that use this level 0 as parent will take advantage of the change tracking file. E is also incorrect.
After eliminating, B, and E, the answers sem to be:
A, C, D
I think the correct answer in A,D and E.
A- To avoid this, Oracle introduced the BLOCK CHANGE TRACKING file – if this was enabled, then a file called the block change tracking file kept information of all changes to blocks since the last backup. This file was read instead of all the blocks in the database to arrive at changed blocks and then these blocks were backed up.
This reduced the backup time considerably – sometimes, especially in the case of Data Warehouse type databases, since changes happened infrequently, incremental backups hardly took minutes to complete as opposed to many hours. This improves RMANs performance as it does not have to scan whole datafiles to detect changed blocks
A & C never comes together as an answer because there is a difference in “sometimes” or “always”. Both statement do not apply to the question.
(A) Backup change tracking will sometimes reduce I/O performed during cumulative incremental
backups.
(C) Backup change tracking will always reduce I/O performed during cumulative incremental
backups.
As per “Database High Availability Best Practices”:
‘Backup to Disk: Best Practices for Minimizing System Resource Consumption (I/O and CPU) If system resource consumption is your primary concern then an Oracle Suggested Recovery Appliance Backup Strategy or incremental backup with a Block Change Tracking enabled consumes the least amount of resources on the database.’
The above Means that answer A is incorrect and answer C is correct.
B is incorrect as per “Database Backup and Recovery User’s Guide”
‘RMAN does not support backup and recovery of the change tracking file. The database resets the change tracking file when it determines that the change tracking file is invalid. If you restore and recover the whole database or a subset, then the database resets the block change tracking file and starts tracking changes again. After you make a level 0 incremental backup, the next incremental backup can use change tracking data.’
Correct answers should be: CDE
My choice – ADE
C is not correct as if the database has changed a lot, saying 90%, from the last backup level 0 the block change tracking file will be used but it will be non optimal. Already tested.
Block change tracking file is good when the database suffers only few changes as it avoid RMAN scanning all datafiles to check the changed blocks.(sorry for my pool english)
Answer is ADE.
http://docs.oracle.com/cd/B19306_01/backup.102/b14192/bkup004.htm#i1032148
ADE
ADE
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A,D,E