DB_WRITER_PROCESSES

Property	Description
Parameter type	Integer
Default value	1 or CPU_COUNT / 8, whichever is greater
Modifiable	No
Range of values	1 to 20
Basic	No

DB_WRITER_PROCESSES is useful for systems that modify data heavily. It specifies the initial number of database writer processes for an instance.

Note:

1. Related parameter:

DBWR_IO_SLAVES: Number of IO slaves

DB_BLOCK_LRU_LATCHES

DB_WRITERS: Oracle 7 parameter

2. This parameter was introduced in Oracle 8.0.4.

3. DB_WRITER_PROCESSES cannot be greater than DB_BLOCK_LRU_LATCHES.

4. DB_WRITER_PROCESSES controls the number of 'DBW' gatherer processes being used by an instance. As of 8.0.4 the 'DBWR' process shows up as 'DBW0' and additional DB writers can be started using this parameter.

5. DBWR operates in a batch-oriented mode: it gathers dirty buffers into a batch and then issues the writes for all buffers in the batch. The writes will use asynchronous IO (AIO) if possible. If AIO is not available then Oracle7 / Oracle8 allow the IO portion of this operation to be parallelised by using multiple DB_WRITERS / DBWR_IO_SLAVES respectively.

6. Setting DB_WRITER_PROCESSES parallelises both the gathering and writing of buffers thus parallelising more of the DBWR activity. Multiple DB writers should be able to produce higher throughput than one DBWR with multiple slaves.

7. If you use DBWR_IO_SLAVES, only ONE database writer process will be used, regardless of the setting for DB_WRITER_PROCESSES. Some releases write messages in the alert log if Oracle did not start the requested number of DB writers.

Eg: "Cannot start more dbwrs than db_block_lru_latches."

"Cannot start multiple dbwrs when using I/O slaves."

Other releases may silently set it to a valid value and write no warnings.

8. 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) = ‘DB_FILE_NAME_CONVERT’;

NAME	VALUE	IS DEFAULT	ISSES_ MODIFIABLE	ISSYS_ MODIFIABLE	ISINSTANCE_ MODIFIABLE	IS DEPRECATED	DESCRIPTION
db_writer_processes	2	TRUE	FALSE	FALSE	FALSE	FALSE	number of background database writer processes to start

Oracle initializatoin parameters