SQL Server Deadlock Resolution – Understanding Causes and Solutions

While working on SQL Server environments, there can be numerous factors that affect the database performance, as well as the workflow of the database administrators. One such issue is deadlocks in SQL Server database. For such cases, it becomes crucial for the users to know about SQL Server deadlock resolution methods and further their implementations to carry out their day-to-day tasks. 

In this blog, we will discuss thoroughly about these deadlocks in SQL Server and how they can be resolved altogether. 

SQL Server Deadlock Issue – A Complete Overview 

Before jumping right to the SQL Server deadlock resolution methods, users must know what deadlocks in SQL Server are and why they occur. A deadlock in SQL Server occurs when there are multiple sessions in the server, and they are waiting for the resources occupied by other sessions. This can be further explained with the help of the given example:

Consider there are two transactions, Transaction A and Transaction B, respectively. 

• Now, Transaction A has a resource, Resource A, locked, and needs Resource B.
• Similarly, Transaction B has the Resource B locked and requires Resource A.
  

Here is a visual representation for the deadlock issue in SQL Server.

In this situation, both transactions, A and B, request the resource locked by each other, and till both the requested resources are released by their respective transactions, no operation can be carried out. This results in a circular loop and permanent deadlock, until it is intervened by the SQL Server. This is the basic definition to what a deadlock in SQL Server is. Now, to understand more about the issue, let’s take a look at the possible causes and challenges raised due to the SQL Server deadlock issue. 

Possible Reasons For SQL Server Deadlocks 

We will now take a look at the possible causes for deadlocks in SQL Server and the challenges created due to the same. Furthermore, we will also learn the best ways for SQL Server deadlock resolution. Proceeding with the causes, let’s understand them one by one. 

1. One of the causes for the deadlocks in SQL Server is the circular loop of resources being occupied by the transactions. Circular loop here refers to the order of the same resources being occupied by different transactions in different orders. 
2. Another cause for the deadlock issue in SQL Server is the long-running queries in SQL Server database. This means the longer a transaction runs, the longer it will hold the lock on the resource.
3. Due to missing indexes in the SQL Server database, the server may scan the bigger portions of the table, which can further lead to deadlocks in the database. 
4. Any SQL queries that operate on multiple rows or tables tend to lock in more resources than required. This can become another common reason for deadlocks to occur in SQL Server. 

These are a few of the causes that lead to the occurrence of deadlocks and further demand that users know about SQL Server deadlock resolution methods. However, these causes only tell how the issue occurs. We will now take a look at the challenges encountered by the users while dealing with these deadlocks. 

Challenges Encountered Due to Deadlocks in SQL Server

• Risk of data loss in the SQL Server database due to transaction rollback.
• Due to SQL Server deadlock issue, users might get error 1205, and often encounter failed operations in the database.
• If the deadlocks are frequent in the database, this can lead to bottlenecks and further result in wastage of I/O resources, CPU, and memory as well. 
• The SQL Server deadlock resolution requires users to first understand the cause of deadlocks in SQL. 
• Inconsistency with data and failures of the application can also occur and cause bigger issues for the users. 

With these challenges, it becomes difficult for users to carry out the required tasks in the SQL Server databases. Hence, it is a must for them to find the most effective solutions to resolve these issues and proceed with their day-to-day tasks seamlessly. We will now take a look at the solutions that will help the users remove deadlocks from SQL Server. 

Best Troubleshooting Ways to Resolve SQL Server Deadlock Issue

After understanding the challenges and the causes for the deadlocks in SQL Server, we will now take a look at the ways to resolve the issue efficiently. 

Method 1: Repair Long-Running Queries in SQL Server for SQL Server Deadlock Resolution

As we read earlier, one of the causes of deadlocks in SQL Server is long-running transactions in the database; therefore, it is crucial to keep the following things in mind:

1. Users can avoid deadlocks by keeping the running transactions short and less complex. 
2. It is also important to avoid any human interference during the transactions. 
3. Lastly, one of the causes for long-running transactions in SQL Server is corruption. Hence, it is important to repair the corruption in the database to avoid long transactions and further prevent deadlocks. 

Method 2: Use Appropriate Indexing in SQL

Another common cause for deadlock we read is the missing or clustered indexes. To avoid the deadlocks caused due to this, the users must keep the indexes non-clustered and maintain proper indexing. This will eventually help the server to scan the tables comparatively faster and further avoid the risk of deadlocks being caused due to missing indexes. 

Method 3: Optimize SQL Server  Queries

This is another troubleshooting way that will help users with SQL Server deadlock resolution. By optimizing the SQL Server queries and understanding the execution plans for the queries, users to understand how SQL is processing any specific query and make any required changes in the execution plan to prevent deadlocks in the database. 

Method 4: Set Up Monitoring and Alerts For Deadlocks

To prevent deadlocks in SQL Server, it is not sufficient to only repair the query execution plans in the database. It is also crucial for the users to understand the reasons to why a query is being executed. There are a few tools offered by Microsoft SQL Server to alert about issues or deadlocks in the database, if any, and further with SQL Server deadlock resolution. The tools are SQL Server Profiler and Extended Events in SQL Server. These SQL Server monitoring tools can help users find and prevent deadlocks in the database efficiently. 

These are the troubleshooting ways that will help users resolve the SQL Server deadlock issue in the database and further allow them to proceed with their day-to-day tasks more efficiently. 

Conclusion

With the help of this technical write-up, we have learned deeply about SQL Server deadlock resolution requirements and the best ways to help users with the same. The deadlocks in the SQL Server database can be caused due to various reasons. We have thoroughly understood these reasons and further suggested the best troubleshooting methods to resolve the issue more effectively.