About me: My name is Maria Zakourdaev. I have more than 10 years experience with SQL Server (starting from SQL Server 6.5). The last five years have been spent mostly on benchmarking different SQL Server features and flows, like data import, indexes impact on DML flows, star transformations in RDBMS, Hierarchic queries and custom OLAP-like aggregations. I was a speaker in the Microsoft Teched (Israel) on the SQL Server track. I am also an active member of the Israel SQL Server Group.

Tuesday, June 8, 2010

WITH (NOLOCK) still places locks !

Did you know, that when you use READ UNCOMMITTED isolation level or WITH (NOLOCK) hint inside the query, it is still places Sch-S (schema stability) locks during compilation and execution and can be blocked by any concurrent trancastion that that holds a Sch-M (schema modification) lock on the table!
So, when using READ UNCOMMITTTED isolation level, keep in mind that READUNCOMMITTED and NOLOCK hints apply only to the data locks and there is nothing you can do with Sch-S lock.

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