FIX: Duplicate Hash Keys Erroneously Generated for Two Distinct Index Key Values

• Microsoft SQL Server version 7.0

SYMPTOMS

Two or greater SQL DML statements issued from different SQL connections, where each connection has its own lock space, experience erroneous blocking or deadlocking for a given index key lock.

CAUSE

When SQL Server places a lock on an index key, the key is "hashed down" to a 6-byte "lock resource", which is used by the lock manager to lock the respective key in the required mode. In this case, a duplicate hash value was incorrectly generated for two distinctly different index keys when taking a key lock in an index.

This can cause a SQL DML statement to block erroneously if a collision occurs between a valid and errant hash value and their respective lock modes are incompatible.

This problem will only manifest itself with key locks.

The net effect of this bug is that the server is overlocking. It is important to note that data integrity is not compromised in any way.

STATUS

Microsoft has confirmed this to be a problem in SQL Server version 7.0. This problem has been corrected in U.S. Service Pack 1 for Microsoft SQL Server version 7.0. For information about downloading and installing the latest SQL Server Service Pack, see http://support.microsoft.com/support/sql/.

For more information, contact your primary support provider.

Additional query words: DEADLOCK BLOCK HASH KEY LOCK 1204 1200 1205

Keywords          : kbbug7.00 kbSQLServ700 kbSQLServ700sp1fix 
Version           : winnt:7.0
Platform          : winnt 
Issue type        : kbbug 

Last Reviewed: June 8, 1999