SQL Server Administration Guide: Troubleshooting

Slow Performance

Experiencing sluggish response times? This is a frequent concern for administrators. Common culprits include:

• Inefficient queries or missing indexes.
• Blocking and deadlocks.
• Insufficient hardware resources (CPU, Memory, I/O).
• Outdated statistics.
• High transaction volume.

Next Steps: Analyze query execution plans, monitor wait statistics, and review resource utilization.

Tip: Use Dynamic Management Views (DMVs) like `sys.dm_exec_query_stats` and `sys.dm_os_wait_stats` for detailed insights.

Connection Issues

Users or applications are unable to connect to the SQL Server instance. Check the following:

• SQL Server Browser service status.
• Firewall rules allowing SQL Server traffic (default port 1433 for TCP/IP).
• SQL Server Configuration Manager to ensure protocols (TCP/IP, Named Pipes) are enabled.
• Network connectivity between client and server.
• Authentication methods (Windows vs. SQL Server Authentication).

Next Steps: Verify network path, check SQL Server error logs for authentication failures.

Database Corruption

Database integrity issues can lead to data loss or inaccessibility. Signs include:

• Errors during database operations (e.g., `Msg 823`, `Msg 824`, `Msg 825`).
• Inability to bring a database online.
• Unexpected application behavior.

Next Steps: Run `DBCC CHECKDB` to identify and potentially repair corruption. Always have a recent backup available.

Important: `DBCC CHECKDB` with repair options can cause data loss. Use with extreme caution and after consulting with Microsoft support if possible.

High CPU Utilization

Sustained high CPU usage can impact all operations. Investigate:

• Long-running queries, especially those performing table scans.
• Excessive recompilations.
• Trigger activity.
• Background maintenance tasks.

Next Steps: Identify top CPU-consuming queries using DMVs or Activity Monitor. Consider query optimization and indexing strategies.

SELECT TOP 50 execution_count, total_elapsed_time, command, sql_handle FROM sys.dm_exec_requests ORDER BY cpu_time DESC;

Out of Memory Errors

SQL Server requires adequate memory to operate efficiently. Common causes for memory pressure:

• Insufficient RAM allocated to SQL Server.
• Memory leaks in applications or within SQL Server itself.
• Excessive memory grant requests for queries.

Next Steps: Monitor SQL Server memory usage (Buffer Cache Hit Ratio, Page Life Expectancy) and the operating system's memory performance counters.

SQL Server Error Logs

The primary source for diagnosing SQL Server issues. Located in the SQL Server instance's `LOG` directory.

View logs using:

• SQL Server Management Studio (SSMS) -> Management -> SQL Server Logs.
• Transact-SQL using `sp_readerrorlog`.

Key events to look for: Errors related to I/O, corruption, memory, deadlocks, and login failures.

EXEC sp_readerrorlog 0, 1, N'Error';

Dynamic Management Views (DMVs)

DMVs provide real-time information about the state of the SQL Server instance. Essential for performance and troubleshooting.

Some critical DMVs include:

• sys.dm_exec_requests: Current requests being processed.
• sys.dm_os_wait_stats: Information about waits encountered by threads.
• sys.dm_db_index_usage_stats: Index usage statistics.
• sys.dm_tran_locks: Information about active lock information.

SQL Server Profiler / Extended Events

Trace server activity to identify specific events causing problems, such as slow queries, deadlocks, or errors.

Recommendation: Extended Events are generally preferred over SQL Server Profiler due to lower overhead.

DBCC Commands

Database Console Commands are powerful tools for checking database consistency and integrity.

• DBCC CHECKDB: Checks the physical and logical integrity of all objects.
• DBCC CHECKTABLE: Checks the integrity of a specific table.
• DBCC CHECKCATALOG: Checks the logical and physical consistency of the database catalog.