Learn more about SQL Server with Nolock hint. Our SQL Server Support team is here to help you with your questions and concerns.

SQL Server with Nolock hint | About

In SQL Server, the NOLOCK table offers performance benefits but also poses risks to data integrity.

Today, we are going to take a look at the NOLOCK hint, its applications, and potential pitfalls.

The NOLOCK hint, when applied to a query, allows SQL Server to retrieve data without considering locks imposed by other transactions.

Although this boosts query performance, it can cause dirty reads. A dirty read occurs when data is read before a transaction commits or rolls back, leading to inconsistencies.

Furthermore, another issue with the NOLOCK hint is nonrepeatable reads. In cases where the same data needs to be read multiple times, using NOLOCK may retrieve different versions of the same row. This behavior can introduce uncertainties in data consistency, especially in dynamic environments.

Our experts recommend being cautious about using the NOLOCK hint. It becomes particularly useful in environments where frequent data reading bottlenecks can be avoided by allowing out-of-sync data.

While NOLOCK provides a solution at the query level, it’s important to note that it can only be used with SELECT statements. Attempts to use it with UPDATE, INSERT, DELETE, or MERGE statements will result in an error. Alternatively, changing the transaction isolation level at the connection level to READ UNCOMMITTED can achieve a similar effect.

In summary, the NOLOCK hint allows for reading data without being blocked by other processes. However, users must weigh the performance benefits against potential dirty reads and nonrepeatable reads. This will help determine if NOLOCK is a suitable solution.

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Conclusion

In brief, our Support Experts introduced us to SQL Server with Nolock hint.