Transaction Isolation Levels

**APPLIES TO:** ![yes](media/yes.png)SQL Server (starting with 2012) ![no](media/no.png)Azure SQL Database ![no](media/no.png)Azure SQL Data Warehouse ![no](media/no.png)Parallel Data Warehouse

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:

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.

Isolation level Supported Honored
READ UNCOMMITTED No Not guaranteed
READ COMMITTED Yes Yes
REPEATABLE READ No No
SNAPSHOT ISOLATION No No
SERIALIZABLE No No