Slow query log analysis

Open the slow query log

The slow query log, as the name implies, records the log of the slow query execution.

Check whether the slow query log is enabled:

show variables like '%slow%';

Open the slow query log. Modifying the MySQL configuration file my.cn is generally under the /etc directory, and restart MySQL after adding the following three lines of configuration.

slow_query_log = ON
slow_launch_time = 2
slow_query_log_file = /usr/local/mysql/data/slow_query.log

slow_launch_time can only be accurate to seconds. If you need more precision, you can use some third-party tools such as pt-query-digest described later.


Note: The MySQL version I use here is 5.6. Different versions of MySQL have different configurations for enabling slow queries. For example, some versions before 5.6 are ong_query_time, long_query_time and log-slow-queries. You can first execute show variables like '%slow%' in the terminal; to see what the specific configuration of the current version is.

You can also open the slow query log in the terminal by setting a global variable:

set  @@global.slow_query_log = ON;

Save the slow query log to a table

MySQL supports saving the slow query log to the mysql.slow_log table. Through @@global.log_output can be set to default to TABLE, only one of FILE and TABLE can be used at the same time.

set @@global.log_output='TABLE';

Reference: http://blog.csdn.net/wulantian/article/details/40296541