Example of how to enable Slow query in MySQL

Preface

Slow query log is a very important function in MySQL. We can enable the slow query log function of MySQL so that we can analyze the execution status and performance of each SQL statement and optimize it accordingly.

This article introduces the relevant content about enabling Slow query in MySQL. Let’s take a look at the detailed introduction.

Here’s how:

1: Log in to the database to check whether Slow query is enabled:

mysql> show variables like 'slow_query%';

2: Enable MySQL slow log:

By default, the value of slow_query_log is OFF, which means that the slow query log is disabled. You can enable it by setting the value of slow_query_log: (This is temporarily enabled and will become invalid after restarting the service. If you want to disable it permanently, remember to add a statement in the myqsl configuration file, see the end of the article)

mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.03 sec)

3: Check whether it is enabled:

mysql> show variables like 'slow_query%'; 

4: Write mysql slow statement to test whether slow data is written:

mysql> select sleep(10) as a, 1 as b; 

5: Check the Mysql Slow file to see if data is written:

At this point, the above Mysql slow startup job is completed!

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Permanently enable MySQL Slow log:

slow_query_log_file slow query log file path

slow_query_log is used to specify whether to open the slow query log

long_query_time Queries exceeding this number of seconds are written to the log

log_output=file must specify a file or a table. If it is a table, the slow query information will be saved in the slow_log table under the mysql database. This point must be made clear. The default value is NONE

Open the my.cnf configuration file and add the following code:

log_output=file
slow_query_log=on ;
slow_query_log_file = /tmp/mysql-slow.log
long_query_time = 2

Summarize

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