When Does `OPTION (RECOMPILE)` Dramatically Improve Query Performance?

OPTION (RECOMPILE) Enhancement: Not Always a Speedy Solution

In database management, performance optimization is crucial. The OPTION (RECOMPILE) can be a useful tool in some scenarios, but it is not always the optimal solution for enhancing query execution speed.

The question at hand involves a peculiar observation where adding OPTION (RECOMPILE) to a query resulted in a drastic performance boost, reducing execution time from over five minutes to half a second. However, removing it caused query execution to revert to its sluggish state.

Understanding OPTION (RECOMPILE)

OPTION (RECOMPILE) instructs the database engine to disregard cached execution plans and recompile the query plan every time it is executed. This option can be beneficial in scenarios where query parameters vary significantly or when underlying data undergoes frequent changes. However, it comes with performance implications as it adds overhead to query execution.

Why Subsequent Queries Are Slow Without OPTION (RECOMPILE)

Recompilation with OPTION (RECOMPILE) ensures that the query utilizes the most optimal execution plan based on current data, even if parameters remain unchanged. Excluding OPTION (RECOMPILE) causes the database to rely on a cached execution plan, which may not be optimal for the current data state. This mismatch can lead to slower query execution.

Rebuilding Statistics and Execution Plan

Before implementing OPTION (RECOMPILE), it is recommended to consider rebuilding database statistics using EXEC sp_updatestats. This ensures that the execution plan is created using the most up-to-date information. Additionally, recreating the execution plan can improve performance.

Dynamic SQL and OPTION (RECOMPILE)

While OPTION (RECOMPILE) may be useful in specific scenarios, it is generally not recommended for parameterized queries. In the provided case, since the query uses dynamic SQL generated by a C# program, dynamic SQL tuning may be necessary to optimize query performance.

Is Frequent Recompilation Necessary?

It is unusual for a query to require recompilation every time it is executed. If frequent recompilation is needed, it suggests underlying data or parameter issues that need to be addressed. Continuously rebuilding execution plans can negatively impact database performance.

In conclusion, while OPTION (RECOMPILE) can be beneficial in some situations, it is important to understand its performance implications. Reconfiguring query parameters and rebuilding database statistics are alternative methods to explore for performance enhancement. Frequent recompilation should be used judiciously and only when there is a clear performance gain.

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