Deadlocks by Database
What is a Deadlock in SQL Server?
A deadlock occurs in SQL Server when two or more processes hold locks on resources that the other processes need, creating a circular dependency. Since neither process can proceed, SQL Server detects the deadlock and terminates one of the processes to break the cycle.
Example of a Deadlock Scenario
- Transaction A locks Table 1 and tries to update Table 2.
- Transaction B locks Table 2 and tries to update Table 1.
- Now, Transaction A is waiting for Table 2, and Transaction B is waiting for Table 1, causing both to be stuck.
- SQL Server detects the deadlock and chooses one transaction to terminate as the deadlock victim.
How SQL Server Handles Deadlocks
- SQL Server automatically detects deadlocks using the Lock Monitor process.
- It chooses a “victim” process to terminate, rolling back its transaction.
- The other process continues execution.
Example Deadlock Error Message:
pgsqlCopyEditMsg 1205, Level 13, State 45, Line 1
Transaction (Process ID 62) was deadlocked on lock resources with another process
and has been chosen as the deadlock victim. Rerun the transaction.
How to Prevent and Resolve Deadlocks
- Use a Consistent Order of Resource Access
- Always update tables in the same order across all transactions.
- Keep Transactions Short and Efficient
- Avoid holding locks longer than necessary.
- Use the Right Isolation Level
- Consider READ COMMITTED SNAPSHOT ISOLATION (RCSI) to reduce locking contention.
- Optimize Indexing
- Proper indexes can reduce scan locks, minimizing the chance of deadlocks.
- Monitor Deadlocks
- Use Database Health Monitor to track and fix deadlocks in your Database. Start with the Deadlocks by DB report then drill down on the databases to find the deadlock queries.
Need Help with Deadlocks?
If you are facing recurring deadlocks, Stedman Solutions’ Managed Services can help optimize your SQL Server for better concurrency and performance.
Learn more here: Stedman Solutions Managed Services