DBWR_IO_SLAVES

Property	Description
Parameter type	Integer
Default value	0
Modifiable	No
Range of values	0 to operating system-dependent
Basic	No

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.

Note:

1. Related parameter: DB_WRITER_PROCESSES, DB_WRITERS

This parameter is introduced in Oracle 8.0.

It replaces in Oracle7.

2. On multi-CPU machines it may be better to set multiple DB_WRITER_PROCESSES rather than have IO slaves.

3. Query for the current value of the parameter

select name, value, isdefault, isses_modifiable, issys_modifiable,

isinstance_modifiable, isdeprecated, description

from v$parameter where upper(name) = ‘DBWR_IO_SLAVES’;

NAME	VALUE	IS DEFAULT	ISSES_ MODIFIABLE	ISSYS_ MODIFIABLE	ISINSTANCE_ MODIFIABLE	IS DEPRECATED	DESCRIPTION
dbwr_io_slaves	0	TRUE	FALSE	FALSE	FALSE	FALSE	DBWR I/O slaves

Oracle initializatoin parameters