Is the DB_WRITER_PROCESSES parameter supported on Windows NT and 2000?

Subject:	Is the DB_WRITER_PROCESSES parameter supported on Windows NT and 2000?
	Doc ID:	Note:149947.1	Type:	BULLETIN
	Last Revision Date:	21-OCT-2005	Status:	PUBLISHED

PURPOSE

  This document is intended to clear up confusion regarding the 

  DB_WRITER_PROCESSES parameter on Windows NT and Windows 2000.

SCOPE & APPLICATION

  The intended audience for this article is Oracle DBAs who are interested in 

  tuning init.ora parameters.

Is the DB_WRITER_PROCESSES parameter supported on Windows NT/Windows 2000?

==========================================================================

Yes, setting the DB_WRITER_PROCESSES parameter to a value greater than one is 

supported starting with the Oracle 8.0 release. The Oracle8i documentation and 

Bug 925955 incorrectly state that this parameter is not supported on 

Windows NT/2000.  Documentation Bug 1839458 has been filed to have the 

documentation corrected in Oracle9i.

Multiple DBWR processes are mainly used to simulate asynchronous I/O when the 

operating system does not support it.  Since Windows NT and Windows 2000 use 

asynchronous I/O by default, using multiple DBWR processes may not necessarily 

improve performance.  Increasing this parameter is also likely to have minimal 

effect on single-CPU systems.  Increasing this parameter could, in fact, reduce 

performance on systems where the CPU's are already over burdened.  In cases 

where the main performance bottleneck is that a single DBWR process cannot keep 

up with the work load, then increasing the value for DB_WRITER_PROCESSES may 

improve performance.

When increasing DB_WRITER_PROCESSES it may also be necessary to increase the

DB_BLOCK_LRU_LATCHES parameter, as each DBWR process requires an LRU latch.

As with any tuning endeavor, the biggest benefit will be gained from addressing 

the largest bottleneck in the system.  Changing any init.ora parameters should 

also be thoroughly tested before implementing the changes in a production

environment.

RELATED DOCUMENTS

  Note 62172.1 Understanding and Tuning Buffer Cache and DBWR in Oracle7, 

                  Oracle8, and Oracle8i

  Note 97291.1 DB_WRITER_PROCESSES or DBWR_IO_SLAVES?

  Bug 1839458  DOC BUG: DB_WRITER_PROCESSES IS INCORRECTLY LISTED AS NOT 

                 SUPPORTED ON NT

  Bug 925955   DB_WRITER_PROCESSES NEEDS TO BE DOCUMENTED AS AN UNSUPPORTED 

                 PARAMETER FOR NT