![]() Let’s enable these trace flags and simulate a SQL Server deadlock situation. Out of these two trace flags, the useful and recommended trace flag is 1222 as it returns the resources, their lock and deadlock information in an XML format. Usually, DBA enables the trace flag 12 to capture the deadlock information in the SQL Server error logs. It is essential to monitor this deadlock situation. The killed process is known as the Deadlock victim. SQL Server automatically monitors the deadlocks every 5 seconds and kills a session so that another transaction can complete the work. This thread also needs to wait for the other transactions to complete User A also requires to read data from the Invoice Details page to complete the transaction, but that page has an Exclusive lock by the user B. It has to wait until the User A releases the Exclusive lock on the page ![]() It tries to place an Intent Shared lock on the Invoice table and shared lock on the page to read the data. User B wants to read the same data user A wants to update. User A also requires an Exclusive lock (X) on the row of the Invoice table User A: Intent Exclusive (IX) lock on the Invoice table and page it requires to modify We can further understand the SQL Server deadlock scenario using the following image. Both the threads cannot process due to insufficient resources. In the following image, we can see that thread A is waiting for the resources held by thread B, and similarly, thread B is waiting for the resources held by thread A. If two processes in SQL Server wants to have exclusive access to a resource held by the other process, it is called a deadlock situation. It is normal behavior and helps to ensure the ACID properties (Atomicity- Consistency – Isolation – Durability). SQL Server obtains locks on required resources to perform specific tasks such as Select, Insert, Update, Delete. Later, we will cover how we can monitor deadlocks using the system_health extended event. Let’s have a quick overview of “Deadlocks in SQL Server”. You can also go through these articles: SQL Server deadlock definition and Overview and What are SQL Server deadlocks and how to monitor them, to understand deadlock in SQL Server. You might face frequent deadlocks issues, and they have a direct impact on the application performance. Performance issues act like an open stage, and you need to look at every aspect such as CPU, RAM, server performance, database performance, indexes, blocking, waits, and SQL Server deadlocks. You should ensure that the database performance is optimal all the time without any impact on the databases. Performance monitoring is a must to do the task for a DBA.
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