如果在目标数据库上配置了I/O从属，RMAN就可以例用I/O从属，为了使用RMAN备份和还原，又两种可用的I/O从属：磁盘I/O从属和磁带I/O从属。

    使用DBWR_IO_SLAVES参数可以配置磁盘I/O从属，这个参数可以被设置为任意值，它的主要作用时在将“脏”缓冲区（即写满的缓冲区）的内容写入磁盘时唤醒另外的DBWR从属来执行磁盘写操作。

SQL> show parameter slave

NAME      TYPE VALUE

------------------------------------ ----------- ------------------------------

backup_tape_io_slaves      boolean FALSE

dbwr_io_slaves      integer 0

SQL> show parameter disk

NAME      TYPE VALUE

------------------------------------ ----------- ------------------------------

asm_diskgroups      string

asm_diskstring      string

disk_asynch_io      boolean TRUE

DBWR_IO_SLAVES

DBWR_IO_SLAVES is relevant only on systems with only one database writer process

( DBW0 ). It specifies the number of I/O server processes used by the  DBW0 process. The

DBW0 process and its server processes always write to disk. By default, the value is  0

and I/O server processes are not used.

If you set  DBWR_IO_SLAVES to a nonzero value, the number of I/O server processes

used by the  ARCH and  LGWR processes is set to  4 . However, the number of I/O server

processes used by Recovery Manager is set to  4 only if asynchronous I/O is disabled

(either your platform does not support asynchronous I/O or  disk_asynch_io is set to

false ).

Typically, I/O server processes are used to simulate asynchronous I/O on platforms

that do not support asynchronous I/O or that implement it inefficiently. However, you

can use I/O server processes even when asynchronous I/O is being used. In that case

the I/O server processes will use asynchronous I/O.

I/O server processes are also useful in database environments with very large I/O

throughput, even if asynchronous I/O is enabled.

BACKUP_TAPE_IO_SLAVES

BACKUP_TAPE_IO_SLAVES specifies whether I/O server processes (also called slaves) are

used by Recovery Manager to back up, copy, or restore data to tape. When the value is

set to  true , Oracle uses an I/O server process to write to or read from a tape device.

When the value is set to  false (the default), Oracle does not use I/O server process for

backups. Instead, the shadow process engaged in the backup accesses the tape device.

PARALLEL

其中的语法：

/*+parallel(table_short_name,cash_number)*/

相关参数

SQL> sho parameter cpu

NAME      TYPE VALUE

------------------------------------ ----------- ------------------------------

cpu_count      integer 2

parallel_threads_per_cpu      integer 2

默认情况下，并行值为上面两个参数的积

举例如下：

select /*+ parallel(table_name 20) */ count(*)from table_name;