Slow queries

The slow query log feature gives the possibility to log queries that take more than x seconds to be executed. This is the first step when investigating a performance issue. To look at the current status, connect to your MariaDB instance and launch it:

MariaDB [(none)]> SHOW GLOBAL VARIABLES LIKE '%SLOW_QUERY%';
+---------------------+---------------------------------+
| Variable_name       | Value                           |
+---------------------+---------------------------------+
| slow_query_log      | OFF                             |
| slow_query_log_file | /var/log/mysql/mariadb-slow.log |
+---------------------+---------------------------------+
2 rows in set (0.00 sec)

Here, we can see the path of the slow query logs. To activate this on the fly, run that SQL command:

MariaDB [(none)]> SET GLOBAL SLOW_QUERY_LOG=1;
Query OK, 0 rows affected (0.00 sec)

The other option is to set in seconds the query delay to mark it as a long query. These long queries will be logged...