FIX: Bad Token or AV If Sp_cursoropen After Dropping Index

ID: Q164215

The information in this article applies to:

Microsoft SQL Server version 6.5

BUG #: 16556 (6.5)

SYMPTOMS

Sp_cursoropen generates an access violation (AV) in xpcursordeclare (on a checked server) or breaks the connection (on a retail server) if you do all of the following:

Open an extended KEYSET_DRIVEN or INSENSITIVE extended cursor on a stored procedure that references a table containing a unique clustered index, non-clustered index, or primary key (PK) constraint.

Close the cursor.

Drop the index or constraint.

Open the cursor again.

The symptom of the broken connection is usually a "bad token" message returned to the client. Slight variations of this may cause an AV in cursornewrow on a checked (or debug) server.

An extended KEYSET_DRIVEN cursor is exposed at the DB-Library API layer as CUR_KEYSET in dbcursoropen() and at the ODBC API layer as SQL_CURSOR_KEYSET_DRIVEN in SQLSetStmtOption(). An extended INSENSITIVE cursor is exposed at the DB-Library layer as CUR_INSENSITIVE in dbcursoropen(), and at the ODBC API layer as SQL_CURSOR_STATIC in SQLSetStmtOption().

WORKAROUND

To work around this problem, do any of the following:

Use a different cursor type.

Use trace flag -T7502 to "Disable caching cursor plans in procedure cache."

Create the stored procedure WITH RECOMPILE.

Drop and re-create the stored procedure after making a table schema change.

STATUS

Microsoft has confirmed this to be a problem in Microsoft SQL Server version 6.5. This problem has been corrected in U.S. Service Pack 3 for Microsoft SQL Server version 6.5. For more information, contact your primary support provider.

MORE INFORMATION

SQL Server supports two different server-side cursor interfaces. One is ANSI SQL cursors, which are exposed through Transact-SQL statements such as DECLARE, FETCH, and so on. The other cursor interface is an extended cursor interface that is accessed through the DB-Library and ODBC APIs. The sp_cursor extended cursor statements are emitted by the DB-Library or ODBC layers in response to certain DB-Library or ODBC API calls. Higher- level interfaces such as Remote Data Objects (RDO) will often encapsulate these API-level calls, so you would need to run a trace utility such as SQL Trace to verify the sp_cursor call being made.

For more information on cursors and concurrency modes, see the on-line documentation and the following article in the Microsoft Knowledge Base:

Q156489 : Overview of SQL Server, ODBC, and DB-Library Cursors

Keywords : kb3rdparty kbhw SSrvDB_Lib SSrvGen
Version : 6.5
Platform : WINDOWS
Issue type : kbbug