Disable caching in MYSQL for True performance testings?

[Sing Lau]

We are trying to optimize some of the slow sql queries. When we first run the query, it's about XX secs, but after the first run, it only takes less than 1 sec for running the same query. It's really hard to compare the results for performance testing or query tunning.

We have disabled the query cache in RDS parameter groups by setting the query cache type,size and limit to 0. And I have set the innodb buffer pool size to the minimum value and the innodb_old_page_pt to 5. But it's still acting the same -- after the first run, it will be much faster. Unless we have to restart the server or wait for couple of hours or days, then it will show the XX secs again.



Can anyone please suggest me how can I disable the caching in MySQL so that we can show the improvement on the query tunning? Thank you in advance.