If you've ever had end users complain that their order submissions are stuck, or routine database queries are timing out for no obvious reason, there's a good chance you're dealing with a deadlock. I've seen new DBAs spend entire afternoons guessing at root causes instead of using the built-in tools that make this process trivial. Learning how to check deadlock in SQL Server doesn't require expensive third-party software, and it will cut your incident resolution time down dramatically. This guide walks through proven, low-effort methods to detect and diagnose deadlocks for both real-time and historical incidents.
How to Check Deadlock in SQL Server Using Built-in System Views
If you're dealing with an active deadlock that's currently impacting users, the fastest way to pull data is through SQL Server's native dynamic management views (DMVs). These views pull real-time data directly from the database engine's internal tracking systems, so you don't have to wait for logs to process to get answers. The most useful views for deadlock detection are sys.dmtrandeadlocks, sys.dmoswaitstats, and sys.dmtran_locks, which you can join together to get a full picture of what's blocked, what resources are held, and which users are impacted.
You can run a simple select query against sys.dmtrandeadlocks to see active deadlock chains, joining with sys.dmexecsessions to pull usernames and application names associated with the blocked processes. That makes it easy to reach out to the right team if a third-party app is sending badly optimized queries. You don't need any third-party tools to pull this data, as it's natively available in all supported SQL Server versions.
The only downside to this method is that it only shows active, ongoing deadlocks. If the deadlock already resolved itself (or was manually killed by another admin) before you run the query, you won't see any record of it in these views. That's why it's best used for active incidents, not for diagnosing deadlocks that happened hours or days earlier.
Capturing Historical Deadlock Data with Extended Events
For historical deadlock tracking, extended events are the gold standard recommended by Microsoft. The old SQL Server Profiler tool was deprecated over a decade ago, and it uses far more system resources than extended events, making it unsuitable for 24/7 production monitoring. Extended events are lightweight enough to run constantly even on high-traffic production servers, with less than 1% performance overhead in most use cases.
To set up deadlock tracking, you'll create a new extended event session that captures the xmldeadlockreport event. You can configure the session to save output to a local file or event file target, so data persists even if the server restarts. When a deadlock occurs, the event will capture a full XML report with details of every process involved, the resources they held, and the order of lock requests that triggered the deadlock.
You can query the saved event files directly with T-SQL, or export the XML reports to open in more user-friendly tools. Extended events capture deadlocks as they happen, even if they resolve automatically, so you can review incidents that happened hours or days earlier. Many DBAs set up their extended event sessions to keep 30 days of deadlock logs, which makes it easy to spot patterns of recurring deadlocks tied to specific application updates or workload changes.
Using the SSMS Deadlock Graph Viewer for Fast Root Cause Analysis
If you don't want to parse raw XML deadlock reports manually, SQL Server Management Studio (SSMS) has a built-in deadlock graph viewer that turns complex event data into a simple visual diagram. You can open saved .xdl deadlock files directly in SSMS, or view deadlock graphs in real time through the Activity Monitor panel.
The graph uses simple visual cues to show you exactly what caused the deadlock: oval nodes represent individual processes running queries, square nodes represent locked resources (like tables, rows, or indexes), and arrows show the direction of lock requests. The process marked with an X is the deadlock victim, the one SQL Server automatically rolled back to break the deadlock. You can hover over any node to see the full text of the query being run, the user running it, and the isolation level of the transaction.
The deadlock graph is the easiest way to quickly identify which query or user action is the root cause of a repeat deadlock. When reviewing a graph, prioritize checking these four details first:
- The deadlock victim's process ID and associated SQL query, to see which operation was rolled back
- The lock types held by each process (exclusive, shared, update) to identify conflicting access patterns
- The order of resource requests, to spot reversed execution order across multiple queries
- The isolation level of each transaction, as higher isolation levels increase deadlock risk
Don't automatically assume the deadlock victim is the problem process; you may need to adjust the other query's execution logic to prevent recurrence. For example, if you have two update queries that modify the order and customer tables in opposite order, you can fix the deadlock by updating both queries to access tables in the same order, even if that means making a small change to the victim query.
Automating Deadlock Alerts for Proactive Monitoring
Checking for deadlocks manually works for one-off incidents, but if you're managing production SQL Server environments, you'll want to set up automated alerts to catch issues before they impact end users. You can use SQL Server Agent to create alerts that trigger whenever a deadlock event is logged in the system event log or extended events session.
You can configure alerts to send email or push notifications to your on-call DBA team, and include key details about the deadlock right in the alert message, so your team can start troubleshooting immediately even if they're not logged into SSMS. Many teams integrate these alerts with Slack or Microsoft Teams channels for on-call notifications, so alerts don't get lost in crowded inboxes. You can also set thresholds to avoid alert fatigue: for example, only trigger a high-priority alert if you see more than 5 deadlocks in a 10-minute window, since single one-off deadlocks are often harmless and resolve automatically.
Proactive deadlock alerts cut down mean time to resolve (MTTR) by 70% for most production database teams, per recent DBA survey data. You can also pair alerts with automated scripts that kill long-running deadlocked processes if they don't resolve within a set time frame, though you should test these scripts thoroughly in a staging environment before running them in production to avoid accidentally rolling back critical transactions.
Deadlocks are a common pain point for every SQL Server admin, but they don't have to be a persistent headache. Taking the time to learn how to check deadlock in SQL Server properly doesn't just resolve immediate outages, it also helps you build more resilient database architectures that avoid deadlocks long term. If you're just getting started, begin with the built-in system views to diagnose active issues, then set up extended events to capture historical data, and add automated alerts to catch issues before they impact users. With these tools in place, you'll spend far less time firefighting deadlocks and more time optimizing your database performance for end users.