How to Detect and Resolve Blocking Sessions in SQL Server

If you've ever worked with SQL Server in a production environment, you've probably encountered a situation where queries suddenly slow down or applications become unresponsive. One of the most common causes of this issue is blocking. Blocking occurs when one query holds a lock on a resource and prevents another query from accessing that same resource. While locking is a normal part of how SQL Server maintains data consistency, excessive blocking can seriously affect database performance. In this article, we’ll explore: What blocking is in SQL Server How to detect blocking sessions How to identify the blocking query Ways to resolve and prevent blocking issues What is Blocking in SQL Server? Blocking happens when a transaction locks a resource (such as a table or row), and another transaction needs access to that same resource. For example: Transaction A updates a row in a table Transaction B tries to read or update the same row Transaction B must wait until Transaction A completes If Tr