SQL Server uses two additional lock types, called schema locks, to prevent table and metadata alteration during query execution. This chapter discusses schema locks in depth, along with other topics such as lock partitioning, which occurs in systems with more than 16 CPUs, and low-priority locks, which were introduced in SQL Server 2014 to reduce blocking during online index rebuilds and partition switch operations.
Schema Modification Locks
SQL Server needs to protect database metadata in order to prevent situations where the table structure is changed in the middle of query execution. ...
