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Q224992: Maintaining Transactional Integrity with OPLOCKS

Article: Q224992
Product(s): Microsoft Windows NT
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): 
Last Modified: 10-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 
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SYMPTOMS
========

Under extreme conditions, some multiuser database applications that use a common
data store over a network connection on a file server may experience
transactional integrity issues or corruption of the database files and/or
indexes stored on the server. This typically applies to some so-called "ISAM
style", or "record oriented" multiuser database applications, not to a
client/server relational system like SQL Server.

CAUSE
=====

If a multiuser or single user database application accesses a common data store
on a Windows NT file server using opportunistic locks (or OPLOCKS), it is
possible for a given user to cache partial transactions on the client systems
hard drive. This is a performance enhancement to the Windows client redirector
to reduce network file I/O between the client and server. The data being cached
on the client redirector is later written back to the server. However, in some
cases, a client system may stop responding (hang), do a hard reboot, lose its
network connection to the server, or experience any number of other technical
difficulties. In such cases, the content of the local cache that has not yet
been written to the server can be lost. As a result, the transaction integrity
of the database structures on the server is compromised and the data on the file
server can become corrupted.

RESOLUTION
==========

To work around this problem, developers writing database applications that
access a network data store should flush file buffers at any time that
represents delineation of a transaction; for example, after a bulk operation, or
prior to closing a file handle, or any time a transaction log is written to.
This can be done by calling the Win32 FlushFileBuffers API Call.

Additional query words:

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Keywords          :  
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400 kbWinNTS400search kbWinNTS400
Version           : winnt:4.0
Issue type        : kbprb

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