When Does OPTION (RECOMPILE) Make SQL Queries Surprisingly Faster?

OPTION (RECOMPILE) Enigma: Why It Can Be Surprisingly Faster Than Its Absence

Introduction

The OPTION (RECOMPILE) clause in SQL Server has always been considered an expensive operation, yet its inclusion in certain queries can lead to significant performance improvements. This paradox has perplexed many developers, leading to questions about the underlying mechanisms and the circumstances under which OPTION (RECOMPILE) is truly advantageous.

The Question

A developer encountered an anomalous situation where adding OPTION (RECOMPILE) to a query drastically reduced its execution time from over five minutes to half a second. This behavior persisted regardless of whether the query was executed from Query Analyzer or through a C# application using SqlCommand.ExecuteReader(). The query call always used the same parameters to eliminate any concerns about sub-optimal parameter sniffing.

The Explanation

Contrary to the assumption that OPTION (RECOMPILE) is always an expensive operation, it can be beneficial in specific scenarios. One common explanation is the need to rebuild the execution plan when the underlying data or parameters change significantly.

When SQL Server creates a stored procedure (or any parameterized query), it caches the most efficient execution plan based on the initial data and parameters. However, subsequent executions with different data or parameters may no longer align with the cached execution plan. In such cases, recompiling the execution plan using OPTION (RECOMPILE) forces SQL Server to optimize it for the current conditions, potentially leading to better performance.

In the specific case presented, the developer should consider rebuilding the query's execution plan and updating statistics using sp_updatestats. This process ensures that the cached execution plan is based on the most up-to-date information, reducing the need for recompilation with each execution.

Key Takeaways

• OPTION (RECOMPILE) can be a viable option in cases where dynamic SQL is used or when data and parameters change significantly.
• Before using OPTION (RECOMPILE), rebuilding the execution plan and updating statistics should be explored to eliminate unnecessary recompilations.
• It is generally unusual for a query to require recompilation on every execution.

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