DOCUMENT:Q176256  22-FEB-2002  [odbc]
TITLE   :FIX: ODBC Driver May Return "TDS Buffer Length Too Large" Error
PRODUCT :Open Database Connectivity (ODBC)
PROD/VER::2.0,3.0
OPER/SYS:
KEYWORDS:kbnetwork

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The information in this article applies to:

 - Microsoft Open Database Connectivity, versions 2.0, 3.0 
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BUG #: 17365

SYMPTOMS
========

In a very slow network environment such as a WAN or dial-up network, where TDS
packets may be delayed during normal transmissions, an ODBC application with
asynchronous mode enabled may return one of the following TDS protocol related
errors, depending on the timing of the network read and the versions of the ODBC
drivers used:

 - Unknown Token Received from SQL Server

 - TDS Buffer Length Too Large, or TDS Buffer Link Too Large

 - Protocol Errors in TDS Stream

 - Memory Allocation Failure

This problem is more likely to occur when you are using TCP/IP sockets than other
IPs.

CAUSE
=====

When an ODBC driver's call to Net-Library fails to return data immediately due
to slow network transmissions, the driver switches to asynchronous mode. When
new TDS data arrives, the ODBC driver resumes its network read. However, under
TCP/IP sockets with a slow and routed network (such as a WAN), where big TDS
packets are typically split across different TCP packets and multiple TDS
packets can be coalesced into a single TCP packet, the resumed network read may
return the remaining part of the previous TDS packet (as it should), but the
driver can be confused by this data stream, which causes the error.

Under other IPCs, multiple TDS packets are typically not coalesced together
during transmissions; therefore, the problem is less likely to occur with other
IPCs.

WORKAROUND
==========

To work around this problem, disable the asynchronous mode. For more information
on how to do this, consult your product documentation or see the following
article in the Microsoft Knowledge Base:

   Q153908 FIX: 16-bit Driver Times Out on Async Calls to SQLTables


STATUS
======

Microsoft has confirmed this to be a problem in the SQL Server ODBC driver
versions 2.5 and 2.65.

A supported fix is now available, but has not been fully regression- tested and
should be applied only to systems experiencing this specific problem. Unless you
are severely impacted by this specific problem, Microsoft recommends that you
wait for the next Service Pack that contains this fix. Contact Microsoft
Technical Support for more information.


Additional query words: netlib dblib db-lib async

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Keywords          : kbnetwork 
Technology        : kbAudDeveloper kbODBCSearch kbODBC300 kbODBC200
Version           : :2.0,3.0
Issue type        : kbbug
Solution Type     : kbfix

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