661.View the Exhibit and examine the output. You execute the following RMAN command to perform the
backup operation:
RMAN> RUN { ALLOCATE CHANNEL c1 DEVICE TYPE disk MAXOPENFILES 8;
BACKUP DATABASE FILESPERSET 4; }
What is the multiplexing level in the preceding backup process?
A. 4
B. 8
C. 7
D. 0
Answer: A
答案解析：
the level of multiplexing is simply the smallest number among FILESPERSET, MAXOPENFILES and total number of datafiles。
You can calculate the level of multiplexing as follows:
Multiplexing = Min (Min (DATAFILES,FILEPERSET) , MAXOPENFILES)
RMAN multiplexing is determined by several factors. For example,
the
FILESPERSET parameter of the BACKUP command determines how many datafiles to put in each backup set. The
MAXOPENFILES parameter of ALLOCATE CHANNEL or CONFIGURE CHANNEL defines how many datafiles RMAN can read from simultaneously. The basic multiplexing algorithm is as follows:
-
Number of files in each backup set
This number is the minimum of the
FILESPERSETsetting and the number of files read by each channel. TheFILESPERSETdefault is 64. -
The level of multiplexing
This is the number of input files simultaneously read and then written into the same backup piece. The level of multiplexing is the minimum of
MAXOPENFILESand the number of files in each backup set. TheMAXOPENFILESdefault is 8.
Suppose that you back up 12 datafiles with one channel when FILEPERSET is set to 4. The level of multiplexing is the lesser of this number and 8. Thus, the channel simultaneously writes blocks from 4 datafiles into each backup piece.
Now suppose that you back up 50 datafiles with one channel. The number of files in each backup set is 50. The level of multiplexing is the lesser of this number and 8. Thus, the channel simultaneously writes blocks from 8 datafiles into each backup piece.
RMAN multiplexing of backup sets is different from media manager multiplexing. One type of media manager multiplexing occurs when the media manager writes the concurrent output from multiple RMAN channels to a single sequential device. Another type occurs when a backup mixes database files and non-database files on the same tape.
http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmcncpt.htm#i1015964