Microsoft KB Archive/154628

= SQL Server logs 17832 with multiple TCP\IP connection requests =

Article ID: 154628

Article Last Modified on 8/22/2007

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APPLIES TO


 * Microsoft SQL Server 7.0 Standard Edition
 * Microsoft SQL Server 6.5 Standard Edition
 * Microsoft SQL Server 6.0 Standard Edition
 * Microsoft SQL Server 2000 Standard Edition
 * Microsoft SQL Server 2005 Workgroup Edition
 * Microsoft SQL Server 2005 Standard Edition
 * Microsoft SQL Server 2005 Developer Edition
 * Microsoft SQL Server 2005 Enterprise Edition

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This article was previously published under Q154628



Important This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows registry



SUMMARY
If SQL Server is hit with multiple and simultaneous TCP/IP connection requests, such as the case with World Wide Web servers, the requests are quickly rejected by responding with a TCP/IP Reset Frame.

This symptom is difficult to detect. If the client application includes error code handling, the native error code is 10061 (WSAECONNREFUSED) for the Open function. On the server, Error 17832 - "Unable to read login packet" appears in the SQL Error log.

If you trace this problem with a protocol analyzer, you can see that some of the connection request frames have been replied to with the TCP Reset bit set, which tells the sending station that the frame has been received, but the server does not have the resources to process the connection request.



MORE INFORMATION
A Winsock application accepts connections on a port by calling a Listen function, which has a backlog parameter specifying the maximum length of the pending-connection queue. The Winsock specification defines the maximum Listen backlog at five and when it exceeds five, TCP/IP issues a Reset.

The backlog for SQL Server can be configured to handle a great number of pending connections by modifying the Windows NT Registry. In some cases, the connection reset issue is resolved due to the modification.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

 Start Registry Editor (REGEDT32.EXE) and locate the following Registry subkey in the HKEY_LOCAL_MACHINE subtree:

\Software\Microsoft\MSSQLServer\MSSQLServer

NOTES:  The corresponding registry subkey in the HKEY_LOCAL_MACHINE subtree for SQL 4.21a is:

\Software\Microsoft\SQLServer\Server

 If SQL Server 6.5 Enterprise Edition is running with a Virtual SQL Server in a clustered environment, you must make the change to virtual server key, rather than the standard:

\Software\Microsoft\MSSQLServer\MSSQLServer

This virtual server key is:

\Software\Microsoft\MSSQLServer$VirtualServerName

\MSSQLServer$VirtualServerName

Value Name: WinsockListenBacklog

Data Type: REG_DWORD

Data: 190

 The new registry location for SQL Server 2000 and for SQL Server 2005:

For a default instance:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\MSSQLServer\SuperSocketNetLib

For a named instance:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\ \MSSQLServer\SuperSocketNetLib

  Select the MSSQLServer subkey for SQL Server 6.5 and SQL Server 7.0, and select the SuperSocketNetLib for SQL Server 2000 and for SQL Server 2005. On the Edit menu, click Add Value.</li> Enter the following:

Value Name: WinsockListenBacklog

Data Type: REG_DWORD

Data:

NOTE: The data value affects overall system resources if it is set to a high value. Windows NT 3.51 has a maximum overall backlog of 100 and Windows NT 4.0 has a maximum overall backlog of 200 for all applications. The suggested method of testing with this value is to set the value in increments of five and observe the results until the connection reset stops.</li> Click OK and quit Registry Editor.</li> Restart SQL Server.</li></ol>

For more information about the Listen function, see the WIN32 SDK Programmer's reference.

For more information about the backlog parameter and Windows NT, click the following article number to view the article in the Microsoft Knowledge Base:

113576 WinSocket app's reject connection requests with Reset Frames

127144 Windows NT WinSock Listen (Backlog) parameter limit

Additional query words: Internet Information Server IIS windows sockets

Keywords: kbnetwork KB154628

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