SyteLine Database Deadlock Diagnosis and Fix Guide
Database deadlocks in SyteLine manifest as the dreaded error "Transaction was deadlocked on lock resources with another process and has been chosen as the deadlock victim." When this error appears during MRP runs, order processing, or inventory transactions, it means two or more database sessions are holding locks that the other session needs. This is not a SyteLine bug—it is a configuration and query optimization problem that can be systematically eliminated.
Capturing and Reading Deadlock Graphs
Before fixing deadlocks, you must capture the deadlock graph to understand which processes and SQL statements are involved. Enable SQL Server's built-in deadlock trace flag 1222 to write detailed deadlock information to the SQL Server Error Log. For more granular analysis, configure an Extended Events session targeting the xml_deadlock_report event. The deadlock graph shows two nodes (victim and survivor) with the exact SQL statements, lock types (KEY, PAGE, OBJECT), and the resource they are contending for.
- Run DBCC TRACEON(1222, -1) on the SyteLine database server to enable global deadlock logging to the SQL Error Log—this is non-intrusive and safe for production
- Create an Extended Events session: CREATE EVENT SESSION [SLDeadlocks] ON SERVER ADD EVENT sqlserver.xml_deadlock_report ADD TARGET package0.event_file(SET filename='C:\DeadlockTraces\SL_Deadlocks.xel') to capture deadlock XML graphs with full call stacks
- Read the deadlock graph: identify the two process nodes, the lock type (KEY lock = row-level, PAGE lock = page-level, OBJECT lock = table-level), and the SQL statement each process was executing at the moment of deadlock
- Look for the pattern: Process A holds KEY lock on table X, waits for KEY lock on table Y; Process B holds KEY lock on table Y, waits for KEY lock on table X—this is the classic SyteLine deadlock between order processing and inventory transactions
Common SyteLine Deadlock Patterns and Fixes
The most frequent SyteLine deadlock occurs between the item_whse table and the co_line table during simultaneous order entry and inventory allocation. The second most common deadlock involves the job_route and jobmatl_mst tables during concurrent MRP planning and production posting. Both patterns are caused by inconsistent lock ordering in custom stored procedures or IDO extensions that access these tables in different sequences.
- Pattern 1: co_line vs item_whse deadlock — ensure all custom procedures that touch both tables access them in the same order: always lock item_whse first, then co_line; refactor any IDO extensions that reverse this order
- Pattern 2: job_route vs jobmatl_mst deadlock during MRP — add WITH (NOLOCK) hints to MRP read queries on job_route where dirty reads are acceptable, or use SNAPSHOT isolation level for the MRP connection string in SyteLine Configuration Manager
- Pattern 3: gl_posting vs journal_mst deadlock during period close — schedule the GL posting background task to run exclusively during a maintenance window when no interactive users are posting journal entries
- Add missing nonclustered indexes on foreign key columns involved in deadlocks: deadlock graphs will show the specific key hash—use sys.dm_db_index_physical_stats to identify which index is contended
- Set the SyteLine database to READ_COMMITTED_SNAPSHOT isolation: ALTER DATABASE [SyteLineDB] SET READ_COMMITTED_SNAPSHOT ON — this eliminates 70-80% of reader-writer deadlocks by using row versioning instead of shared locks
Preventing Future Deadlocks
Deadlock prevention is an ongoing discipline. After resolving acute deadlocks, implement proactive monitoring and design guidelines that prevent new deadlocks from being introduced. The combination of SNAPSHOT isolation, consistent lock ordering conventions, and automated deadlock alerting will keep your SyteLine database contention-free.
- Create a SQL Server Alert on error 1205 (deadlock victim) that sends an email notification with the deadlock graph XML attached—configure in SQL Server Agent > Alerts > New Alert > Error Number 1205
- Establish a lock ordering convention document for all custom SyteLine development: alphabetical table access order within any transaction (e.g., co_line before item, item before item_whse)
- Review all custom stored procedures with sp_WhoIsActive during peak hours to identify long-running transactions that hold locks for more than 5 seconds—these are deadlock candidates
- Use Query Store (SQL Server 2016+) to track regressed query plans that suddenly start taking row-level locks instead of index seeks, which is a common trigger for new deadlock patterns after statistics updates
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