Knowledge Base

SNA Server Fails to Release Memory in SNA TCP/IP Interface DLL

Article ID: 142037

Article Last Modified on 11/19/2003

APPLIES TO

Microsoft SNA Server 2.1, when used with:
- Microsoft Windows NT 4.0
Microsoft SNA Server 3.0, when used with:
- Microsoft Windows NT 4.0

This article was previously published under Q142037

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

A Windows NT Server running SNA Server 2.11 slows down when running SNA Server clients that use TCP/IP.

This problem occurs sporadically.

CAUSE

An SNA Server Service internal trace shows that SNA Server TCP/IP asynchronous writes are not completing. These pending writes continue to consume system memory. The SNA Server client configured for TCP/IP may continuously attempt to open a session with the SNA Server. The SNA Server tries to send a response but the write never completes and is unable to release the i/o (input/output) buffer memory.

RESOLUTION

SNAIP.DLL now aborts a connection if the connection has more than 100 pending writes queued. Every time a connection is aborted, an event 706 is logged in the application log:

   Event Id: 706

   Description:
   Connection to client %2 has been aborted due to too many (%1) pending
   writes.

   Explanation

   SNA Server has aborted a TCP/IP connection because asynchronous writes
   queued on the connection have not completed.

   ACTION

   Provide network support personnel with the event log file(s) related to
   SNA, and SNA internal trace file(s). For information about SNA log and
   trace files, see the "Microsoft SNA Server Administration Guide."

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

You can configure the abort limit by adding the MaxPendingWrites registry parameter:

Go to the HKEY_LOCAL_MACHINE subtree under the following subkey:
```
System\CurrentControlSet\Services\SnaBase\Parameters\SnaTcp
                        
```
If the SnaTcp subkey does not exist, it will need to be added it before going onto the next step.

Add the following information:

Value Name: MaxPendingWrites
      Data Type:  REG_DWORD
      Data:       <value> (decimal)

where <value> is by default 100 (decimal) with the updated SNAIP.DLL file (see below) installed.

Microsoft has updated the following files to correct this problem:

<snaroot>\SYSTEM\SNAIP.DLL
<snaroot>\SYSTEM\SNAEVENT.DLL

STATUS

Microsoft has confirmed this to be a problem in SNA Server for Windows NT. This problem was corrected in the latest SNA Server for Windows NT, 2.11 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

Additional query words: prodsna

Keywords: kbbug kbfix kbnetwork KB142037

Microsoft KB Archive/142037

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