RMAN深入解析之--内存中的RMAN
RMAN会在内存中创建一些缓冲区，然后通过这些缓冲区将数据块 写入到备份中。内存的利用与PGA(有时是SGA)的总体大小有关。
内存缓冲区分为输入缓冲区和输出缓冲区。输入缓冲区（input buffer）填充从备份文件中读取数据块；输出缓冲区（output buffer）则在执行内存对内存的写操作时填充需要备份的数据块，一旦输出缓冲区被填满，输出缓冲区的内容就会被写入到备份位置。
RMAN的内存利用
在磁盘上备份会使用PGA内存空间作为备份缓冲区，PGA内存空间从用于信道进程的内存空间中分配。如果操作系统没有配置本地异步I/O,则可以利用DBWR_IO_SLAVES参数使用I/O丛属来填充内存中的输入缓冲。如果设置DBWR_IO_SLAVES参数为任意的非零值，则RMAN会自动分配4个I/O从属来协调输入缓冲区中数据块加载。为了实现这一功能，RMAN必须利用一个共享内存区域。因此，用于磁盘备份的内存缓冲区会被推入共享池，如果存在大池，则被推入大池。如果没有使用磁带I/O从属，则会在PGA中分配用于磁带输出缓冲区的内存。
查看RMAN备份输入缓冲区的信息：
[oracle@rh7 ~]$ rman target /
Recovery Manager: Release 11.2.0.1.0 - Production on Tue Jun 17 18:30:27 2014
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
connected to target database: PROD (DBID=239333010)
RMAN> backup database;
Starting backup at 17-JUN-14
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=43 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00001 name=/u01/app/oracle/oradata/prod/system01.dbf
input datafile file number=00002 name=/u01/app/oracle/oradata/prod/sysaux01.dbf
input datafile file number=00005 name=/u01/app/oracle/oradata/prod/example01.dbf
input datafile file number=00003 name=/u01/app/oracle/oradata/prod/undotbs01.dbf
input datafile file number=00004 name=/u01/app/oracle/oradata/prod/users01.dbf
channel ORA_DISK_1: starting piece 1 at 17-JUN-14
channel ORA_DISK_1: finished piece 1 at 17-JUN-14
piece handle=/u01/app/oracle/product/11.2.0/db_1/dbs/04pb386s_1_1 tag=TAG20140617T183051 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:01:42
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
including current SPFILE in backup set
channel ORA_DISK_1: starting piece 1 at 17-JUN-14
channel ORA_DISK_1: finished piece 1 at 17-JUN-14
piece handle=/u01/app/oracle/product/11.2.0/db_1/dbs/05pb38a3_1_1 tag=TAG20140617T183051 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 17-JUN-14
查看缓冲区信息：
sql>select set_count,device_type,type,filename,buffer_size,buffer_count,open_time,close_time
2 from v$backup_async_io
3* order by set_count,type,open_time,close_time
SET_COUNT DEVICE_TYP TYPE FILENAME BUFFER_SIZE BUFFER_COUNT OPEN_TIME CLOSE_TIM
---------- ---------- --------- ---------------------------------------- ----------- ------------ --------- ---------
4 DISK AGGREGATE 0 0 17-JUN-14 17-JUN-14
4 DISK INPUT /u01/app/oracle/oradata/prod/example01.d 524288 6 17-JUN-14 17-JUN-14
bf
4 DISK INPUT /u01/app/oracle/oradata/prod/sysaux01.db 524288 6 17-JUN-14 17-JUN-14
f
4 DISK INPUT /u01/app/oracle/oradata/prod/system01.db 524288 6 17-JUN-14
f
4 DISK INPUT /u01/app/oracle/oradata/prod/users01.dbf 524288 6 17-JUN-14 17-JUN-14
4 DISK INPUT /u01/app/oracle/oradata/prod/undotbs01.d 524288 6 17-JUN-14 17-JUN-14
bf
4 DISK OUTPUT /u01/app/oracle/product/11.2.0/db_1/dbs/ 1048576 4 17-JUN-14
04pb386s_1_1
7 rows selected.
Elapsed: 00:00:00.02
18:32:19 SYS@ prod>
