MySQL Load Monitor
I wrote this script in a rush when our MySQL server started blocking my PHP application because of (at the time) unknown reasons. The sole intention is to warn when a large number of MySQL processes get queued up which is often a cause for concern.
It will send you an email with a very basic var_dump() style list of the MySQL processes and the number that is queued.
This is not intended to be used permanently but can at least warn you in desperate times so you are prepared for calls from people that cannot access your application or website!
Compatibility
Will work on PHP 5.2 and above, and requires PDO for MySQL access. Intended to be used with the Linux crontab.
Configuration
Copy mysql_load_check_config.dist to mysql_load_check_config.php and edit it, filling in your database and email configuration.
The most important setting is MIN_PROCSSES_TO_WARN which will determine if it should raise an alert or not. In MySQL enter SHOW PROCESSLIST; to see what your idle process count looks like and make a judgement on what you want it to alert on. On a busy server you might only care if the processes get backed up over 100, to be alerted when it's most likely that a rogue SQL query has locked tables and is causing a bottleneck.
If you only wish to test it on the command line, you can disable the email functionality with EMAIL_ENABLED.
How to use
The script is meant to be run on the console or in Crontab.
Using on the console
Simply run it with the php executable:
php mysql_load_check.php
If you are only testing set the MIN_PROCSSES_TO_WARN quite low so you can trigger a warning and see it working.
Automatic load checks with Crontab
Using with crontab is only useful if email alerts are enabled, so check this is working on the console (as above) first.
On the linux console enter the crontab edit page with:
crontab -e
and enter a line like it will check every 5 minutes, or change to whatever you like:
*/5 * * * * php /path/to/files/mysql_load_check.php
Save and exit the crontab editor and as a sanity check choose a low MIN_PROCESSES_TO_WARN setting and ensure alert emails are coming through, then change it to the real setting you wish to warn on.