Deadlocks and excessive blocking is the bane of many development teams and DBAs. They are often at the root of performance problems. Understanding each of these problems and how to solve the root cause can be difficult. I find that the terms are used interchangeably and frequently mixed. Understanding the difference, and diagnosing the issue is crucial to resolving these problems. Both happen due to incompatible locks being held or requested on tables, but they differ in their root cause. Some troubleshooting methods work for both problems, but deadlocks generally require logic changes to fix permanently and consistently.
This post is aimed at giving a general background on blocking and deadlocks. It also shows some basic methods to find these problems and general ways to fix them. I’m not going into extreme detail. This is just an introduction.