Microsoft® SQL Server 2012 Unleashed

Schema Locks

SQL Server uses schema locks to maintain structural integrity of SQL Server tables. Unlike other types of locks that provide isolation for the data, schema locks provide isolation for the schema of database objects, such as tables, views, and indexes within a transaction. The Lock Manager uses two types of schema locks:

Schema stability locks—When a transaction is referencing either an index or a data page, SQL Server places a schema stability lock on the object. This ensures that no other process can modify the schema of an object—such as dropping an index or dropping or altering a stored procedure or table—while other processes ...