Which action takes place when a file checkpoint occurs?
A.
The checkpoint position is advanced in the checkpoint queue.
B.
All buffers for a checkpointed file that were modified before a specific SCN are written to disk by
DBWn and the SCN is stored in the control file.
C.
The Database Writer process (DBWn) writes all dirty buffers in the buffer cache to data files.
D.
The Log Writer process (LGWR) writes all redo entries in the log buffer to online redo log files.
Explanation:
C
B
All dirty buffers are write to the datafiles only during FULL CHECKPOINT (When you for example issue: shutdown immediate).
I think it’s C because LGWR is called only if some redo has not been already processed, so in theory it’s possible that LGWR isn’t called at all.
Sayed’s advice is nearly every time correct. This is a rare exception. B seems to be correct: ‘The database writes to disk all buffers modified by redo before a specific target.’
DBWn is and has to be lazy. Only in full checkpoint he writes all dirty buffer to datafiles.
Additionally the question is ‘a file checkpoint’ which is a clear hint that ‘all dirty buffers’ can NOT be the correct answer.
exactly
C is correct.
B says: “All buffers for a checkpointed file that were modified before a specific SCN”
But it should be like “All buffers for a checkpointed file that were modified AFTER a specific SCN”
Buffers BEFORE a specific SCN should have been already written to disk then SCN have been given.
C
B is correct.
Checkpoint SCN
Every data file has a data file checkpoint SCN, which you can view in V$DATAFILE.CHECKPOINT_CHANGE#. All changes with an SCN lower than this SCN are guaranteed to be in the file. When a level 0 incremental backup is restored, the restored data file contains the checkpoint SCN that it had when the level 0 was created. When a level 1 incremental backup is applied to a file, the checkpoint SCN of the file is advanced to the checkpoint SCN that the file had when the incremental level 1 backup was created.
-> https://docs.oracle.com/database/121/BRADV/rcmcncpt.htm#BRADV90078
I think B is correct
Every data file has a data file checkpoint SCN.
These checkpoints occur in a variety of situations, including making a tablespace read-only or taking it offline normal, shrinking a data file, or executing ALTER TABLESPACE BEGIN BACKUP.
when these checkpoints occur, the database writes to disk all buffers modified by redo before a specific target
By the book of certification OCA Administrator Certified Assosiate Study Guide
” A checkpoint is when the DBWn process writes all the dirty buffers to the data files. When a checkpoint occurs, Oracle must update the control file and each data file header to record the checkpoint. This update is done by the checkpoint process (CKPT); the DBWn process writes the actual data blocks to the data files.”
So, I think that the answer is correct.
Answer: C
B
The Correct Answer this C.
Checkpoint: Updates the data file headers following a checkpoint
event.
Thomas. “OCA: Oracle®Database 12c Administrator Certified Associate”, pp. 467
C
C
I think The answer is be according to the document below
https://docs.oracle.com/cd/B19306_01/server.102/b14220/process.htm#i7261
When a checkpoint occurs, Oracle must update the headers of all datafiles to record the details of the checkpoint. This is done by the CKPT process. The CKPT process does not write blocks to disk; DBWn always performs that work.
As you see it is written must update the headers of all datafiles
I think The answer is C according to the document below