MySQL slow query operation example analysis [enable, test, confirm, etc.]

yum -y install mariadb-server mariadb-devel

more /etc/my.cnf.d/server.cnf

[mariadb]
slow_query_log=ON
slow_query_log_file=/usr/local/mysql/data/slow.log
long_query_time=1

systemctl start mariadb

MariaDB [(none)]> show variables like '%slow_query%';
+---------------------+--------------------------------+
| Variable_name | Value |
+---------------------+--------------------------------+
| slow_query_log | ON |
| slow_query_log_file | /usr/local/mysql/data/slow.log |
+---------------------+--------------------------------+
2 rows in set (0.00 sec)

MariaDB [(none)]> show variables like 'long_query_time';
+-----------------+----------+
| Variable_name | Value |
+-----------------+----------+
| long_query_time | 1.000000 |
+-----------------+----------+
1 row in set (0.00 sec)

#If you don't have slow query enabled, you can enable it in the command line mysql> set global slow_query_log=1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> select sleep(2);
+----------+
| sleep(2) |
+----------+
| 0 |
+----------+
1 row in set (2.00 sec)

[root@localhost ~]# more /usr/local/mysql/data/slow.log
/usr/libexec/mysqld, Version: 5.5.60-MariaDB (MariaDB Server). started with:
Tcp port: 0 Unix socket: /var/lib/mysql/mysql.sock
Time Id Command Argument
# Time: 180930 23:51:07
# User@Host: root[root] @ localhost []
# Thread_id: 2 Schema: QC_hit: No
# Query_time: 2.001017 Lock_time: 0.000000 Rows_sent: 1 Rows_examined: 0
SET timestamp=1538322667;
select sleep(2);

MariaDB [(none)]> show full processlist; #View the state slow query in progress +----+------+-----------+------+---------+------+------------+-----------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
| 3 | root | localhost | NULL | Query | 9 | User sleep | select sleep(10) | 0.000 |
| 4 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0.000 |
+----+------+-----------+------+---------+------+------------+-----------------------+----------+
2 rows in set (0.00 sec)

MariaDB [(none)]> show full processlist; #Check the state slow query has ended, but the user is logged in +----+------+-----------+------+---------+------+-------+-----------------------+----------+
| Id | User | Host | db | Command | Time | State | Info | Progress |
+----+------+-----------+------+---------+-------+-------+-----------------------+----------+
| 3 | root | localhost | NULL | Sleep | 1 | | NULL | 0.000 |
| 4 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0.000 |
+----+------+-----------+------+---------+-------+-------+-----------------------+----------+
2 rows in set (0.00 sec)