Xloc Table Hint in SQL Server

The xlock hint is used to specify that an exclusive lock should be acquired on the specified resource (Row, page or table). An exclusive lock present other transaction from reading or modifying the locked resource until the lock is released.

This hint is typically used in scenarios where we want to ensure that no other transaction can access the lock resource while our transaction is in progress. It can block other transaction so use it judiciously to avoid performance issue. Be careful when we are using this hint, it can increase the risk of deadlock.

It is a powerful hint in SQL server for ensuring data integrity by preventing concurrent access to specific resource.

See the example

We have table order_details . here we are reading the data where order_Status =’A’ in the transaction and select is not yet committed or rollbacked and another user want to update the records which order_Status=’A’ to ‘Processing’ we can not update because these records already locked.

BEGIN TRANSACTION; -- Start the transaction and acquire row-level locks for the selected rows SELECT * FROM orders_details WITH (XLOCK) WHERE order_status = 'A'  --COMMIT TRANSACTION;

 

Another window we are updating these records.

update  orders_details  set order_status='Processing' WHERE order_status = 'A';

Update is not yet done.

Lets commit the transaction.

As soon as committed the transaction update is competed successfully.

By incorporating the XLOCK hint, exclusive locks are acquired on the specified rows, ensuring that no other transactions can access or modify them until the current transaction completes. This prevents interference and maintains data integrity during critical database operations. However, it’s essential to use XLOCK judiciously, considering its impact on concurrency and ensuring that the duration of the locks is minimized to avoid blocking other transactions unnecessarily.