KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q102630: LAN Manager Heuristics and Windows NT Registry Entries

Article: Q102630
Product(s): Microsoft Windows NT
Version(s): 3.1,4.0
Operating System(s): 
Keyword(s): kbenv
Last Modified: 28-FEB-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Server versions 3.1, 4.0 
- Microsoft Windows NT Workstation versions 3.1, 4.0 
- Microsoft Windows NT Advanced Server, version 3.1 
-------------------------------------------------------------------------------

SUMMARY
=======

Several of the wrkheuristic and srvheuristic values in the Microsoft LAN Manager
LANMAN.INI file directly correspond to Registry entry values on a Microsoft
Windows NT or Microsoft Windows NT Advanced Server machine. Some of those values
are described below.

WORKSTATION HEURISTICS
----------------------

The following LAN Manager workstation heuristics map to Windows NT workstation
parameters in the Registry at HKEY_LOCAL_MACHINE\System\
CurrentControlSet\Services\LanmanWorkstation\Parameters:

WRKHEURISTIC: 0
UseOpportunisticLocking

Indicates whether the redirector should use opportunistic-locking performance
enhancement. This parameter should be disabled only to isolate problems.

  Default: 1 (True)

WRKHEURISTIC: 2
UseUnlockBehind

Indicates whether the redirector will complete an unlock operation before it has
received confirmation from the server that the unlock operation has completed.
Disable this parameter only to isolate problems or to guarantee that all unlock
operations complete on the server before completing the application's unlock
request.

  Default: 1 (true)

WRKHEURISTIC: 4
BufNamedPipes

Indicates whether the redirector should buffer character-mode named pipes.
Disable this parameter to guarantee that all pipe write operations are flushed
to the server immediately and to disable read ahead on character-mode named
pipes.

  Default: 1 (True)

WRKHEURISTIC: 5
UseLockReadUnlock

Indicates whether the redirector will use the lock-and-read and write-and-unlock
performance enhancements.

When this value is enabled, it generally provides a significant performance
benefit. However, database applications that lock a range and don't allow data
within that range to be read will suffer performance degradation unless this
parameter is disabled.

  Default: 1 (True)

WRKHEURISTIC: 11
UseRawRead and UseRawWrite

Enables the raw-read and write optimization. This provides a significant
performance enhancement on a local area network.

  Default: 1 (True)

WRKHEURISTIC: 19
Use512ByteMaxTransfer

Specifies whether the redirector should only send a maximum of 512 bytes in a
request to an MS-Net server regardless of the servers- negotiated buffer size.
If this parameter is disabled, request transfers from the Windows NT redirector
could cause the MS-Net server to crash.

  Default: 0 (False)

WRKHEURISTIC: 23
BufFilesDenyWrite

Specifies whether the redirector should cache files that are opened with only
FILE_SHARE_READ sharing access. Usually, if a file is opened with
FILE_SHARE_READ specified, the file cannot be buffered because other processes
may also be reading that file. This optimization allows the redirector to buffer
such files. This optimization is safe because no process can write to the file.
Disable this parameter if it is necessary to preserve the strict semantics of
the sharing modes specified.

  Default: 1 (true)

WRKHEURISTIC: 24
BufReadOnlyFiles

Specifies whether the redirector should cache files that are read- only. Usually,
if a read-only file is opened, the file cannot be buffered because other
processes may also be reading that file. This optimization allows the redirector
to buffer such files. This optimization is safe because no process can write to
the file. However, another user can modify the file to enable writing to the
file, causing loss of data. Disable this parameter if it is necessary to
preserve the strict semantics of the sharing modes specified.

  Default: 1 (true)

SERVER HEURISTICS
-----------------

The following LAN Manager server heuristics map to Windows NT Registry entries at
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\ LanmanServer\Parameters:

SRVHEURISTIC: 5
EnableFCOpens

Specifies whether MS-DOS file control blocks (FCBs) are folded together so that
multiple remote opens are performed as a single open on the server. This saves
resources on the server.

  Range: Boolean
  Default: 1 (True)

SRVHEURISTIC: 6
ThreadPriority

Specifies the priority of all server threads in relation to the base priority of
the process. Higher priority can give better server performance at the cost of
local responsiveness. Lower priority balances server needs with the needs of
other processes on the system.

  Range: 5-50 secs (LAN Manager); 0-15 secs (Windows NT)
  Default: 5 secs (LAN Manager); 5 secs (Windows NT)

SRVHEURISTIC: 10
ScavTimeout

Specifies the time that the scavenger remains idle before waking up to service
requests. A smaller value for this parameter improves the response of the server
to various events, but costs CPU cycles.

  Range: 5-50 secs (LAN Manager); 1-300 secs (Windows NT)
  Default: 5 secs (LAN Manager); 30 secs (Windows NT)

SRVHEURISTIC: 11
EnableSoftCompat

Specifies whether the server maps it to a normal open request with shared-read
access when the server receives a compatibility open request with read access.
Mapping such requests allows several MS-DOS computers to open a single file for
read access.

  Range: 0, 1, 2, 3(LAN Manager); 0 (False), 1 (True) (Windows NT)
  Default: 2 (LAN Manager); 1 (Windows NT)

SRVHEURISTIC: 15
OplockBreakWait

Specifies the time that the server waits for a client to respond to an oplock
break request. Smaller values can allow detection of crashed clients more
quickly, but can potentially cause loss of cached data.

  Range: 35-640 secs (LAN Manager); 10-180 secs (Windows NT)
  Default: 35 secs (LAN Manager); 35 secs (Windows NT)

REFERENCES
==========

Documentation from MS LAN Manager Upgrade to Windows NT Advanced Server LAN
Manager documentation

Additional query words: prodnt wrkheuristic srvheuristic

======================================================================
Keywords          : kbenv 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTW310 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS310 kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNTS310search kbWinNT310Search kbWinNTW310Search
Version           : :3.1,4.0

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.