OCP-1Z0-053-V12.02-661题

最新推荐文章于 2016-11-24 16:13:09 发布

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最新推荐文章于 2016-11-24 16:13:09 发布

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分类专栏： OCP-1Z0-053 OCP11g解析

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本文深入探讨了使用RMAN执行备份操作时的多路复用概念，解释了多路复用级别的计算方法，并通过实例说明了RMAN如何在备份过程中进行文件的高效读取和写入。

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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 FILESPERSET setting and the number of files read by each channel. The FILESPERSET default 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 MAXOPENFILES and the number of files in each backup set. The MAXOPENFILES default 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