UPDLOCK Hint in SQL Queries: Reasons to Avoid and Best Practices

The UPDLOCK hint in SQL Server is used to indicate that the lock obtained on the selected rows is to be held until the end of the transaction. This lock ensures that no other transaction can obtain an exclusive lock on the rows while the transaction is in progress. Essentially, it upgrades a shared lock to an update lock, which is a precursor to an exclusive lock.

Why UPDLOCK Should Be Avoided

While UPDLOCK can be useful in certain scenarios, it should be used sparingly due to the following reasons:

1. Causes Blocking

• Blocking Behavior: When a transaction uses UPDLOCK, it acquires an update lock on the rows it accesses. This prevents other transactions from obtaining exclusive locks on the same rows. If another transaction tries to update these rows, it will be blocked until the first transaction releases its lock.
• Chain Reactions: This can lead to a chain reaction where multiple transactions are blocked, creating a bottleneck that slows down the overall performance of the database.

2. Increases Server Wait Times

• Wait Types: The use of UPDLOCK increases the likelihood of encountering specific wait types such as LCK_M_U (Lock: Update). These wait types indicate that a transaction is waiting to acquire an update lock, which can significantly increase server wait times.
• Transaction Duration: If the transaction holding the UPDLOCK is long-running, it exacerbates the issue by holding the lock for an extended period, further increasing wait times for other transactions.

Best Practices for Using UPDLOCK

1. Limit Scope and Duration

• Short Transactions: Keep transactions short and limit the duration of locks to reduce the likelihood of blocking. Avoid using UPDLOCK in long-running transactions.
• Specific Scenarios: Use UPDLOCK only in specific scenarios where it is absolutely necessary, such as when you need to ensure that a row will not be updated between a select and an update operation within the same transaction.

2. Monitor and Tune

• Monitoring Tools: Use monitoring tools like Database Health Monitor to track and analyze locking and blocking issues in your SQL Server environment.
• Regular Reviews: Regularly review and optimize your queries and transactions to ensure that they do not unnecessarily hold locks for extended periods.

Conclusion

While UPDLOCK can be a useful tool in certain situations, its frequent use can lead to significant performance issues due to blocking and increased server wait times. By understanding its impact and following best practices, you can ensure that your SQL Server environment remains efficient and responsive.

For more detailed guidance and expert assistance with SQL Server performance tuning, consider leveraging Stedman Solutions’ managed services. Our team of SQL Server specialists can help you optimize your database operations and prevent performance bottlenecks. Learn more about our services here and download the Database Health Monitor for continuous monitoring and alerting here.