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PC Ext: Explanation of Opportunistic Locking on Windows NT
Article ID: 129202 - View products that this article applies to.
This article was previously published under Q129202
With Exclusive Oplock, if a file is opened in a non-exclusive (deny none) mode, the redirector requests an opportunistic lock of the entire file. As long as no other process has the file open, the server will grant this oplock, giving the redirector exclusive access to the specified file. This will allow the redirector to perform read-ahead, write-behind, and lock caching, as long as no other process tries to open the file.
When a second process attempts to open the file, the original owner will be asked to Break Oplock or Break to Level II Oplock. At that point, the redirector must invalidate cached data, flush writes and locks, and release the oplock, or close the file.
Opportunistic Locking level II, provides a method for granting read access to a file by more than one workstation, and these workstations can cache read data locally (read-ahead). As long as no station writes to the file, multiple stations can have the file open with level II oplock.
An illustration of how level II oplocks work:
WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.
Workstation Service Entries
Indicates whether the redirector should use opportunistic-locking (oplock) performance enhancement. This parameter should be disabled only to isolate problems.
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet \Services\LanmanWorkstation\Parameters UseOpportunisticLocking REG_DWORD 0 or 1 Default: 1 (true)
Server Service Entries
Specifies whether the server allows clients to use oplocks on files. Oplocks are a significant performance enhancement, but have the potential to cause lost cached data on some networks, particularly wide-area networks.
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet \Services\LanmanServer\Parameters EnableOplocks REG_DWORD 0 or 1 Default: 1 (true)
Specifies the minimum link throughput allowed by the server before it disables raw and opportunistic locks for this connection.
MinLinkThroughput REG_DWORD 0 to infinite bytes per second Default: 0
Specifies the maximum time allowed for a link delay. If delays exceed this number, the server disables raw I/O and opportunistic locking for this connection.
MaxLinkDelay REG_DWORD 0 to 100,000 seconds Default: 60
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.
OplockBreakWait REG_DWORD 10 to 180 seconds Default: 35
Article ID: 129202 - Last Review: December 5, 2003 - Revision: 3.0