How SQL Server commands to clear caches before running a performance comparison?

Question

When comparing the execution time of two different queries, it's important to clear the cache to make sure that the execution of the first query does not alter the performance of the second. In a Google Search, I could find these commands: DBCC FREESYSTEMCACHE DBCC FREESESSIONCACHE DBCC FREEPROCCACHE In fact, my queries are taking a more realistic time to complete after several executions than before. However, I'm not sure this is the recommended technique.

What's the best practice?

Endo Kobayashi · Accepted Answer

Personally, for a common query the 2nd and subsequent executions matter more. Are you testing disk IO or query performance? Assuming your query runs often and is critical, then you want to measure that under real life conditions you can easily SQL server clear cache efficiently. And you don't want to clear prod server caches each time... If you want, you can: Personally, for a common query the 2nd and subsequent executions matter more. Are you testing disk IO or query performance? Assuming your query runs often and is critical, then you want to measure that under real life conditions you can easily SQL server clear cache efficiently. And you don't want to clear prod server caches each time...If you want, you can: Personally, for a common query the 2nd and subsequent executions matter more. Are you testing disk IO or query performance? Assuming your query runs often and is critical, then you want to measure that under real life conditions you can easily SQL server clear cache efficiently. And you don't want to clear prod server caches each time... If you want, you can:

How SQL Server commands to clear caches before running a performance comparison?

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