How do I test the real execution time of a query?

Question

I get one slow query in Mysql slow query log. Mysql slow query log shows the query need more than 4 seconds to execute.

I run this query in phpmyadmin, it takes 3 seconds. When I run it again, it takes only 0.0002 seconds. I guess there is a DB Cache or something. When I run it in second time, it executing time might not be accurate.

For this kind of situation(executing time is quick), how do I test the real execution time of the query?

Answer 1

For testing purpose only you can use SQL_NO_CACHE

SELECT SQL_NO_CACHE * FROM `table` .....

other way you can set query_cache_type to 0 for current session

SET SESSION query_cache_type=0;

SQL_NO_CACHE

Query Cache Configuration

Answer 2

If you are talking about preventing MySQL from caching the result, you can use the SQL_NO_CACHE keyword. (eg: SELECT SQL_NO_CACHE * FROM table1)

Answer 3

You can modify your query a little before executing it second time.

So following two queries are regarded as different by the query cache:

SELECT * FROM tbl_name
Select * from tbl_name

A query cannot be cached if it contains some special functions like CONNECTION_ID(). You can add this function to your query:

SELECT *,CONNECTION_ID() FROM tbl_name

How the Query Cache Operates