Debugging

Logging all performed queries to MySQL

By default SQL queries are not logged for performance and memory saving reasons. If we need to log queries for debugging, we can activate general query log.

In MySQL/MariaDB we first check if general query log is enabled:

SHOW VARIABLES LIKE 'general_log%';

This outputs the status and the file where it logs to:

+------------------+------------+
| Variable_name    | Value      |
+------------------+------------+
| general_log      | OFF        |
| general_log_file | femas1.log |
+------------------+------------+ 

We can find out the path of the log file with:

SHOW VARIABLES LIKE 'datadir';

We can activate general log with:

SET GLOBAL general_log = 1;

However it's recommended to keep it disabled:

SET GLOBAL general_log = 0;

More useful for production is the slow query log, which logs only slow queries:

SET GLOBAL slow_query_log = 1;
SET GLOBAL long_query_time = 1; -- in seconds