When Does OPTION (RECOMPILE) Make SQL Queries Faster?

Why OPTION (RECOMPILE) Might Be Faster: An Explanation

In the context of SQL Server, the OPTION (RECOMPILE) clause plays a crucial role in boosting query performance. While it's commonly understood that this option is resource-intensive, understanding its underlying mechanisms sheds light on scenarios where it outperforms queries without it.

Plan Caching and Parameter Sniffing

When a query is executed in SQL Server, an execution plan is generated to optimize its access to the database. This plan is cached based on the specific parameters used during the query's execution. However, when the data or parameter values change significantly, the cached plan may no longer be optimal.

The Case for OPTION (RECOMPILE)

In certain situations, the benefits of rebuilding the execution plan with each query execution can outweigh the performance hit associated with recompilation. This is particularly the case when:

• Dynamic SQL: Queries constructed dynamically often involve varying parameters or data, rendering the cached plan less effective. OPTION (RECOMPILE) ensures that the most appropriate plan is used each time.
• Stale Statistics: If the database statistics are outdated, the cached plan may not incorporate recent changes in data distribution, leading to suboptimal performance. Recompiling the plan with OPTION (RECOMPILE) ensures that it uses the most up-to-date statistics.

Caveats and Case Study

Despite its advantages, OPTION (RECOMPILE) should not be blindly employed. Regular rebuilding of execution plans can be resource-intensive and may introduce unnecessary overhead.

In the case provided, the significant performance improvement with OPTION (RECOMPILE) likely stems from outdated statistics. By running the sp_updatestats command to update statistics and recreating the execution plan without recompilation, the query's performance could be optimized without the need for OPTION (RECOMPILE) on every execution.

Conclusion

OPTION (RECOMPILE) serves as a valuable tool in specific scenarios when dynamic SQL or outdated statistics impact query performance. However, rebuilding statistics and optimizing execution plans without recompilation should be explored as potential solutions before resorting to this option.

The above is the detailed content of When Does OPTION (RECOMPILE) Make SQL Queries Faster?. For more information, please follow other related articles on the PHP Chinese website!