FIX: ODS Errors During Attention Signal May Cause SQL Server to Stop Responding (236447)

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 is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next SQL Server service pack that contains this hotfix.

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 about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

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.

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: