FIX: ODS Errors During Attention Signal May Cause SQL Server to Stop Responding

ID: Q236447

The information in this article applies to:

Microsoft SQL Server version 6.5

BUG #: 18781 (SQLBUG_65)

SYMPTOMS

If an Open Data Services (ODS) error, such as:

Error : 17805
Invalid buffer received from client

Is encountered during the processing of an attention signal, the SQL Server process may stop responding (hang) and will not allow any new connections or existing queries to execute.

If the following message appears in the error log:

Process <spid> entered sequencer without owning dataserver semaphore

The hang of the server is likely imminent. However, the hang can also occur without seeing this message.

When the server stops responding, it will continue to allow connection requests to queue up until the maximum number of connections are reached (as defined by the user connections configuration value). However, to the user of these new connections, it will appear as though they are hung. When the maximum user connection limit is encountered, you will begin to see the following message repeated in the error log for each new user who tries to connect:

Unable to connect. The maximum number of '<max user conn>' configured user connections are already connected.
System Administrator can configure to a higher value with sp_configure.

If you have a high number (for example, 1,000 or more) of user connections configured, you may also encounter the following message before reaching the maximum number of user connections on SQL Server build 6.50.427 or greater:

Error : 17802
Creation of server event thread failed

RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next SQL Server service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

The English version of this fix should have the following file attributes or later:


   Version       File name     Platform
   ------------------------------------
   6.50.451      Sql451i.exe   Intel
   6.50.451      Sql451a.exe   Alpha

NOTE: Due to file dependencies, the most recent hotfix or feature that contains the above files may also contain additional files.

WORKAROUND

Reducing the number of attention signals sent to SQL Server may reduce the frequency of the problem. You can reduce the number of attention signals sent from an application by ensuring that all results are processed. Avoid canceling a query or closing a connection before all results are processed.

Because error 17805 is the primary condition to encounter an ODS error when processing an attention signal and this error has only been observed when using the TCP/IP network library, switching to another network library may also reduce the possibility of encountering this problem.

STATUS

Microsoft has confirmed this to be a problem in SQL Server version 6.5.

MORE INFORMATION

The primary symptom for the hang to occur is seeing an ODS error during processing of attention signals. The most common error that could be encountered under these conditions is:

Error : 17805
Invalid buffer received from client

Unfortunately, other issues may cause ODS to raise error 17805 when processing packets other than attention signals. There is no way based on the error 17805 to see whether it occurs when processing attention signals or some other packet. Using a tool like SQLTrace or Network Monitor can help you determine if attention signals are being sent to the server.

Additional query words: hang hangs hung errorlog max attn attentions

Keywords : SSrvODS kbbug6.50
Version : winnt:6.5
Platform : winnt
Issue type : kbbug