Inside Microsoft® SQL Server™ 2005, Fourth Edition

Lock Compatibility

Two locks are compatible if one lock can be granted while another lock on the same resource is held by a different process. If a lock requested for a resource is not compatible with a lock currently being held, the requesting connection must wait for the lock. For example, if a shared page lock exists on a page, another process requesting a shared page lock for the same page is granted the lock because the two lock types are compatible. But a process that requests an exclusive lock for the same page is not granted the lock because an exclusive lock is not compatible with the shared lock already held. Figure 8-2 summarizes the compatibility of locks in SQL Server 2005. Along the top are all the lock modes that a process might ...