How do you resolve parameter-sniffing problems?

How do you resolve parameter-sniffing problems?

First, confirm the issue by executing the query with different parameter values and comparing the actual execution plans, row estimates and performance.

Common solutions

1. Update statistics

Outdated statistics may produce incorrect estimates.

UPDATE STATISTICS dbo.Orders;

2. Recompile each execution

Creates a plan based on the current parameter value.

SELECT *
FROM Orders
WHERE CustomerId = @CustomerId
OPTION (RECOMPILE);

Best when execution frequency is low or parameter values vary greatly. It adds compilation cost.

3. Optimize for a specific value

OPTION (OPTIMIZE FOR (@CustomerId = 100));

Useful when one value represents most executions.

4. Optimize for an average value

OPTION (OPTIMIZE FOR UNKNOWN);

Creates a more general plan using statistical estimates. It may not be best for extreme values.

5. Use separate query paths

Run different queries for small and large result sets.

IF @CustomerId = 1
    -- Query suitable for a large result
ELSE
    -- Query suitable for a small result

6. Use parameterized dynamic SQL

This can generate separate cached plans for meaningfully different query structures.

7. Use Query Store hints

Apply hints such as RECOMPILE without changing the application code.

Key points

• Do not clear the entire plan cache; it affects all queries and is usually only a temporary fix.

• Choose the solution based on data distribution, query frequency and compilation cost.

• SQL Server 2022+ can use Parameter Sensitive Plan optimization to maintain multiple plans for different parameter ranges.