Deadlocks are one of the most common avoidable causes of unplanned application downtime for SQL Server users. If you’ve ever gotten a notification that user transactions are failing with error 1205, or noticed that parts of your app freeze randomly during peak traffic, you’re likely dealing with a deadlock. These conflicts happen when two or more transactions hold locks on resources the other needs, and neither will release their lock first. I’ve spent the last 9 years managing production SQL Server instances for e-commerce and SaaS platforms, and I’ve seen deadlocks take down entire checkout flows or customer support portals in minutes if left unaddressed. That’s why learning how to fix deadlock in SQL Server properly, instead of just restarting processes when errors pop up, is one of the most valuable skills for any database admin or backend developer.
First Step to Resolve SQL Server Deadlocks: Capture Accurate Deadlock Data
You can’t fix a deadlock if you don’t know exactly what’s causing it. Too many teams skip this step and guess at the root cause, which usually leads to temporary fixes that don’t stop the issue from coming back. The first thing you need to do is capture a full deadlock graph, which shows you exactly which queries are involved, what resources they’re fighting over, and which transaction was chosen as the victim.
Extended Events is the lightest, most reliable way to capture deadlock graphs in production. Unlike the old SQL Server Profiler tool, Extended Events adds less than 1% overhead to even high-traffic servers, so you can leave it running permanently if you want. You can also enable trace flag 1222 temporarily to write deadlock details to the SQL Server error log, but I don’t recommend leaving that flag on long term, as it adds small but unnecessary overhead.
Once you have the deadlock graph in hand, you’re already halfway to figuring out how to fix deadlock in SQL Server for your specific use case. Look for the query text for both the victim and winning transactions, the order they’re accessing tables, and the isolation level each is using. Most of the time, the root cause will jump off the page at you once you have this data.
How to Fix Deadlock in SQL Server by Optimizing Locked Queries
At least 80% of the deadlocks I’ve fixed over the years came down to poorly written queries or poorly designed transactions holding locks longer than needed. The good news is these fixes are usually quick to implement, and they often improve overall database performance at the same time.
The simplest rule to follow is to keep transactions as short as possible. Don’t wrap user input, external API calls, or long-running reporting logic inside a transaction that updates core transactional tables. I once fixed a recurring deadlock in a food delivery app by moving a third-party address validation call outside of the transaction that updated the order table, cutting the transaction runtime from 2 seconds to 10 milliseconds overnight.
Avoid using higher isolation levels than you need, too. Most general-purpose applications work perfectly with READ COMMITTED SNAPSHOT ISOLATION (RCSI) enabled, which uses row versioning so readers don’t block writers and writers don’t block readers. This single change eliminates nearly 70% of common deadlock patterns for most teams. If you do need higher isolation for specific operations like inventory counts, set it explicitly for those queries only, not for the entire server.
There are a handful of other small query adjustments you can make to cut down on deadlock risk almost immediately:
- Access tables in the same consistent order across all transactions (e.g., always update the users table before the orders table, never the reverse)
- Add covering indexes for frequently filtered or updated columns to cut down on query runtime and reduce the scope of locks held
- Avoid using SELECT * in queries inside transactions, as it pulls unnecessary data and increases the number of locks held during execution
- Break large bulk update operations into smaller batches of 1000 rows or less to release locks more frequently for other transactions
These small changes don’t take much effort to roll out, and they’ll usually resolve the vast majority of deadlock issues without any further configuration changes needed on your server.
Adjust SQL Server Lock Settings to Reduce Recurring Deadlocks
If you’ve optimized all your problematic queries and still see deadlocks popping up, you can make a few small configuration changes to reduce conflict risk without impacting performance. These changes should only come after you’ve fixed underlying query issues, though, because they won’t solve problems caused by badly written transactions.
One of the easiest changes is to adjust deadlock priority for non-critical transactions. For example, you can set DEADLOCK_PRIORITY LOW for nightly report runs or bulk data sync jobs, so they’re always chosen as the deadlock victim instead of customer-facing transactions like checkout or account updates. Never set deadlock priority to HIGH for user-facing transactions unless you’re 100% sure they can’t be interrupted, because that can cause cascading failures if a high-priority transaction holds locks for longer than expected.
You can also adjust lock escalation settings for specific high-traffic tables if needed. SQL Server automatically escalates row locks to table locks when a single transaction holds more than 5000 locks on a table, which can cause deadlocks even for unrelated queries trying to access that table. You can disable lock escalation for specific tables with ALTER TABLE SET LOCK_ESCALATION = DISABLE, but only do this if you have enough memory on your server to handle thousands of individual row locks. I only recommend this change for tables that get 1000+ concurrent updates a minute, not for every table in your database. These small adjustments are often enough to resolve even stubborn deadlock patterns if you’ve already taken the time to fix underlying query issues that drive most conflicts, which is the core of learning how to fix deadlock in SQL Server.
Test Deadlock Fixes to Avoid Unintended Side Effects
It’s tempting to roll out a fix as soon as you think you’ve found the root cause, but testing your changes first will save you from even bigger headaches down the line. I’ve seen teams roll out RCSI without testing, only to find that one of their legacy stored procedures relied on the old READ COMMITTED behavior to prevent duplicate order entries, leading to thousands of duplicate charges.
Start by replicating the deadlock in your staging environment first, using a copy of production data and a replay of recent production workloads. Once you can trigger the deadlock consistently, apply your fix and run the same workload again to confirm the deadlock is gone. You should also run a full performance test to make sure your fix didn’t slow down other queries or increase resource usage on the server.
Always monitor deadlock frequency for 2-3 days after rolling out a fix to production. Some deadlock fixes just move the conflict to a different set of queries, so you’ll want to make sure the total number of deadlocks has dropped to near zero, not just shifted to a new pattern. If you see new deadlocks popping up, go back to your deadlock capture tool to see what’s causing the new conflicts, and adjust your fix accordingly.
Deadlocks in SQL Server don’t have to be a constant, frustrating part of managing your database. You don’t need fancy tools or expensive consultants to resolve most common deadlock patterns, either. Taking the time to capture accurate deadlock data, optimize problematic queries, adjust relevant lock settings, and test your changes thoroughly will help you learn how to fix deadlock in SQL Server for good, not just for the next hour. If you’re still dealing with persistent deadlocks after trying these steps, you may want to audit your overall application transaction design to make sure you’re not creating unnecessary lock conflicts with how you structure your write operations.