Parameter Sniffing in SQL Server Query Performance Tuning

Identify Parameter Sniffing Symptoms

Analyze a set of query execution times and execution plans to determine if parameter sniffing is causing performance issues.

Expected output: A report identifying queries affected by parameter sniffing with supporting evidence.

Hint: Look for queries with varying execution times and check if the execution plan is reused.

Apply OPTIMIZE FOR Hint

Modify a stored procedure to include the OPTIMIZE FOR hint for a common parameter value and measure performance changes.

Expected output: Improved or stabilized query performance for typical parameter values.

Hint: Choose a parameter value that represents typical workload conditions.

Parameter sniffing is when SQL Server's query optimizer uses the parameter values from the first execution of a query to generate and cache an execution plan, which is then reused for subsequent executions regardless of parameter changes.

If the initial parameter values used to create the execution plan are not representative of typical values, the cached plan may be inefficient for other parameter values, causing slow query execution and increased resource consumption.

One method is using the OPTION (RECOMPILE) hint to force SQL Server to recompile the execution plan for each query execution, optimizing it for the current parameters.