How to Find the Cause of an SQL Server Deadlock Using Trace Flags and Error Log

When dealing with database performance issues, one common problem is an SQL Server deadlock, where two or more transactions are blocked due to a lock conflict. To troubleshoot this issue, you can use trace flags and the SQL error log to identify the cause of the deadlock. In this article, we will explore how to do so.

Firstly, it's essential to understand that there is an overhead associated with activating these trace flags, so you should disable them once you've finished capturing the deadlock information you were interested in. To activate the trace flags, use the following commands: 1204 and 1222. These trace flags allow you to track the resources involved in a deadlock.

Once the flags are activated, you can find the deadlock information by accessing the `sp_readerrorlog` stored procedure. This stored procedure provides a wide range of information about the errors that have occurred in your SQL Server database.

When running SQL statements, it's not uncommon to encounter deadlocks, especially when dealing with concurrent updates. For example, consider the following scenario: two transactions, one by Bob and another by Alice, attempting to update the same row simultaneously. This can lead to a deadlock situation where both transactions are blocked, waiting for each other to release their locks.

In this article, we will explore how to use trace flags and the SQL error log to identify the cause of an SQL Server deadlock. We'll also discuss the importance of understanding the concurrency control mechanisms used by relational database systems, including 2PL (Two-Phase Locking) and MVCC (Multi-Version Concurrency Control).

In conclusion, identifying the cause of an SQL Server deadlock can be a complex task, but using trace flags and the SQL error log can help you to troubleshoot the issue. By understanding the concurrency control mechanisms used by relational database systems, you can better appreciate the importance of tracking deadlocks and avoiding them in your production system.

Sql deadlock report