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Why is My SQL Query Much Slower in ASP.NET than in SSMS?

Linda Hamilton
Release: 2025-01-03 08:13:39
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Why is My SQL Query Much Slower in ASP.NET than in SSMS?

Performance Disparity between SQL Server Management Studio and ASP.NET Applications

When executing SQL queries, it is not uncommon to encounter significant performance discrepancies between SQL Server Management Studio (SSMS) and web applications. Such performance issues can be puzzling and frustrating. In this case, a query that runs in seconds in SSMS takes minutes to execute in an ASP.NET application.

Exploring Parameter Sniffing

One potential explanation for this disparity is a phenomenon known as parameter sniffing. Parameter sniffing occurs when the SQL Server query optimizer uses different execution plans for the same query based on the data types and values of the parameters supplied during compilation.

In the provided query, the @customerID parameter is used to filter the results. When the query is executed in SSMS, the optimizer may choose a more efficient execution plan based on the specific value of @customerID. However, when the query is executed in the ASP.NET application, the optimizer may compile the query using a less optimal plan due to the different data type or value of @customerID at that moment.

Mitigating Parameter Sniffing

To mitigate parameter sniffing, consider the following strategies:

  • Use Parameterized Queries: Use parameterized queries instead of concatenating parameter values into the query string, as this forces the optimizer to re-evaluate the execution plan for each execution.
  • Recompile Execution Plan: If the execution plan needs to be recompiled based on changing parameter values, use query hints such as OPTION (RECOMPILE) or OPTIMIZE FOR(@customerID).
  • Use Query Plans: If recompiling the execution plan is problematic, consider using cached or parameterized query plans to ensure that the same plan is always used, regardless of parameter values.

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