Transaction Isolation Levels
SQL Server does not guarantee that lock hints will be honored in queries that access metadata through catalog views, compatibility views, information schema views, metadata-emitting built-in functions.
Internally, the SQL Server Database Engine only honors the READ COMMITTED isolation level for metadata access. If a transaction has an isolation level that is, for example, SERIALIZABLE and within the transaction, an attempt is made to access metadata by using catalog views or metadata-emitting built-in functions, those queries will run until they are completed as READ COMMITTED. However, under snapshot isolation, access to metadata might fail because of concurrent DDL operations. This is because metadata is not versioned. Therefore, accessing the following under snapshot isolation might fail:
Information Schema Views
Metadata-emitting built-in functions
sp_help group of stored procedures
SQL Server Native Client catalog procedures
Dynamic management views and functions
For more information about isolation levels, see SET TRANSACTION ISOLATION LEVEL (Transact-SQL).
The following table provides a summary of metadata access under various isolation levels.
|READ UNCOMMITTED||No||Not guaranteed|