Deadlock — the transaction was deadlocked on resources with another process
What 1205 Means
The 1205 error on the SQL Server engine-errors indicates deadlock — the transaction was deadlocked on resources with another process. This typically occurs due to two processes holding locks that the other process requires.
Deadlocks occur when two or more tasks permanently block each other because each task has a lock on a resource which the other tasks are trying to lock. SQL Server detects this and terminates one of the sessions as a victim.
Technical Background
Deadlocks are a normal part of database operations in high-concurrency environments. They are not errors in the traditional sense but rather a 'stalemate' that SQL Server resolves by choosing one transaction to be the 'victim' and rolling it back.
SQL Server uses a background process called the Deadlock Monitor to detect these cycles. The monitor periodically checks for blocked tasks and, if it finds a circular dependency, it terminates the transaction that is least 'expensive' to roll back.
Common Causes
- Two processes holding locks that the other process requires
- Inefficient query patterns causing long-held locks
- Updating tables in a different order across different transactions
Typical Scenarios
- High-traffic systems updating the same rows from multiple threads
- Complex reports running simultaneously with data entry operations
What to Know
Designing application code to handle error 1205 through automated retries is a standard resilience pattern. Deadlock prevention involves consistent table access orders and minimizing transaction duration.
Frequently Asked Questions
Common questions about SQL Server 1205 error
No, deadlocks are almost always a result of application logic and query design patterns.