QUESTION 6
View the exhibit and examine the output.
NOTE: Exhibit Estimated, Not The Actual Exhibit
Which statement can be an inference from the output?
A. The FRA disk group has an asynchronous I/O bottleneck
B. The least number of I/Os are performed on the lastdata file in the list
C. The number of times that the backup or restore process directed the OS to wait until an I/O was complete is
the highest for the last data file in the list
D. The number of times that the backup or restore process made an OS call to poll for I/O completion in
Nonblocking mode is the least for the FRA disk group
Answer: A
同90题：http://blog.csdn.net/rlhua/article/details/18793669
Explanation/Reference:
Section: Managing Database Performance & Tuning
NO EXHIBIT - ANSWER impossible / A) is set as placeholder
Oracle Press 1Z0-053 Exam Guide, Chapter 8: Monitoring and Tuning RMAN
Monitoring Asynchronous I/O
To monitor asynchronous I/O operations, you use thedynamic performance view V$BACKUP_ASYNC_IO.
The key columns to watch are the following:
- IO_COUNT: Number of I/Os performed on thefile
- LONG_WAITS: Number of times the backup or restore process had to tell the OS to wait for the I/O to
complete
- SHORT_WAIT_TIME_TOTAL: Total time, in hundredths of a second, taken for nonblocking polling for
I/O completion
- LONG_WAIT_TIME_TOTAL: Total time, in hundredths of a second, taken while blocking waits for
I/O completion
The largest ratio of LONG_WAITS to IO_COUNT is a likely bottleneck in the backup process.
SHORT_WAIT_TIME_TOTAL and LONG_WAIT_TIME_TOTAL are also indicators of a bottleneck if they are
nonzero.
This example identifies two input files with nonzero ratios:
SQL> select long_waits / io_count waitcountratio, filename
2 from v$backup_async_io
3 where long_waits / io_count > 0
4 order by long_waits / io_count desc;
WAITCOUNTRATIO FILENAME
-------------- ----------------------------------------
.248201439 /u01/oradata/bkup/6bjmt1e3_1_1.
2 /u01/app/oracle/flash_recovery_area/HR/autobackup/2008_07_31/o1_mf_s_661554862_% u_.bkpSQL>
For these two files, you may consider increasing the multiplexing to decrease or eliminate the wait times when backing them up.
Exam Tip:
If you are using synchronous I/O but you have set BACKUP_DISK_IO_SLAVES to TRUE, then the I/O
performance is monitored in V$BACKUP_ASYNC_IO.