Knowledge Base

Understanding Blocking vs. Deadlocks

What It Is Blocking is when one process holds a lock another needs. Deadlocks occur when two or more processes block each other permanently. Why...

Written By: Brandon Adams
Last Updated: August 22, 2025
2 minutes read

What It Is

Blocking is when one process holds a lock another needs. Deadlocks occur when two or more processes block each other permanently.

Why It Matters

Blocking slows performance, but resolves itself.
Deadlocks require SQL Server to terminate one process.

How to Spot It

Use SQL Profiler or Extended Events.
Monitor deadlock graphs and blocking chains.
Real-time alerts via SQL Diagnostic Manager.

How to Fix or Address It

Optimize query order and indexing.
Use WITH (NOLOCK) cautiously.
Implement deadlock retry logic in apps.

Key Takeaway

Not all locking is bad—but understanding blocking and deadlocks prevents downtime and frustration.

How Can Idera Help?

Identify and resolve lock issues faster by using SQL Diagnostic Manager. For more information or to start a free trial, visit us HERE.

Brandon Adams

SQL Server Tools Product Marketing Manager

With over two decades of experience in SQL, SaaS, data center infrastructure, power quality, data storage, disaster recovery, and IT security, Brandon bridges technical expertise with business needs to help organizations get the most out of their data environments. He focuses on making complex database and infrastructure challenges easier to understand, enabling DBAs and IT leaders to improve performance, strengthen security, and simplify management.