When Does OPTION (RECOMPILE) Actually Improve SQL Query Performance?

OPTION (RECOMPILE): An Explanation for its Unexpected Performance Advantages

Introduction

It is commonly assumed that utilizing the OPTION (RECOMPILE) in SQL queries is an expensive operation, as it requires the creation of a new lookup strategy for the query. However, in certain cases, it has been observed that adding OPTION (RECOMPILE) significantly improves query performance. This article aims to address the reasons behind this phenomenon and the trade-offs involved.

Why OPTION (RECOMPILE) May Improve Performance

OPTION (RECOMPILE) ensures that the execution plan for a query is rebuilt every time the query is executed. While this is generally considered an expensive operation, it can be beneficial in scenarios where:

• Significant changes to underlying data: The data used by the query may have undergone substantial changes since the last execution, resulting in an outdated execution plan.
• Dynamic SQL: The query is dynamic, with parameters or data sources varying across executions, leading to different optimal execution plans.

Rebuild Execution Plans vs. Plan Caching

When a parameterized query is first executed, SQL Server typically determines and caches an execution plan based on the current data and parameters used. This caching is intended to optimize performance by reusing the plan for subsequent executions.

However, if the underlying data or parameters change significantly, the cached plan may no longer be optimal. OPTION (RECOMPILE) bypasses this caching mechanism, forcing the creation of a new plan for each execution.

Trade-offs and Recommendations

While OPTION (RECOMPILE) can improve performance in certain scenarios, it should be used judiciously as it comes with some trade-offs:

• Performance overhead: Rebuilding the execution plan incurs additional computational costs.
• Increased memory usage: New execution plans are stored in memory, which can lead to memory issues.

Therefore, it is recommended to carefully assess the potential benefits and trade-offs before opting for OPTION (RECOMPILE). Consider updating statistics and rebuilding the execution plan without using OPTION (RECOMPILE) as an initial troubleshooting step.

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