Check mysql-connections

Overview

Checks the connection usage rate, the rate of aborted connections and if name resolution is active for new connections on MySQL/MariaDB. Logic is taken from MySQLTuner script:mysql_stats(), v1.9.8.

Hints:

See additional notes for all mysql monitoring plugins

Fact Sheet

Check Plugin Download	https://github.com/Linuxfabrik/monitoring-plugins/tree/main/check-plugins/mysql-connections
Check Interval Recommendation	Once a minute
Can be called without parameters	Yes
Compiled for	Linux, Windows
Requirements	User with no privileges, locked down to `127.0.0.1` - for example `monitoring\@127.0.0.1`. Usernames in MySQL/MariaDB are limited to 16 chars in specific versions.
3rd Party Python modules	`pymysql`

Help

usage: mysql-connections [-h] [-V] [--always-ok]
                         [--defaults-file DEFAULTS_FILE]
                         [--defaults-group DEFAULTS_GROUP]
                         [--ignore-name-resolution] [--timeout TIMEOUT]

Checks the connection usage rate, the rate of aborted connections and if name
resolution is active for new connections on MySQL/MariaDB.

options:
  -h, --help            show this help message and exit
  -V, --version         show program's version number and exit
  --always-ok           Always returns OK.
  --defaults-file DEFAULTS_FILE
                        Specifies a cnf file to read parameters like user,
                        host and password from (instead of specifying them on
                        the command line), for example
                        `/var/spool/icinga2/.my.cnf`. Default:
                        /var/spool/icinga2/.my.cnf
  --defaults-group DEFAULTS_GROUP
                        Group/section to read from in the cnf file. Default:
                        client
  --ignore-name-resolution
                        Do not check if name resolution is active. Default:
                        False
  --timeout TIMEOUT     Network timeout in seconds. Default: 3 (seconds)

Usage Examples

./mysql-connections --defaults-file=/var/spool/icinga2/.my.cnf

Output:

0.0% aborted connections (0.0/3.1K); current 90% used (136/151, 5 threads running) [WARNING]; peak 93% used (140/151) at 2023-10-06 10:08:47; ; interactive_timeout = 1h, wait_timeout = 1; Name resolution is active [WARNING]

Recommendations:
* Reduce or eliminate unclosed connections and network issues.
* Reduce or eliminate persistent connections to reduce connection usage (set connections > 10, wait_timeout < 28800 and/or interactive_timeout < 28800).
* A reverse name resolution is made for each new connection and can reduce performance. Configure your accounts with ip or subnets only, then update your configuration with skip-name-resolve=ON.

States

WARN if the number of connections is more than 85% of the maximum possible number of simultaneous client connections (setting max_connections).
WARN if the number of aborted connections is more than 3% of all client connections.
WARN if name resolution is active (if –ignore-name-resolution is ommitted).

Perfdata / Metrics

Name	Type	Description
mysql_aborted_connects	Continous Counter	Value of the MySQL `Aborted_connects` status variable. Number of failed server connection attempts. This can be due to a client using an incorrect password, a client not having privileges to connect to a database, a connection packet not containing the correct information, or if it takes more than connect_timeout seconds to get a connect packet.
mysql_connections	Continous Counter	Value of the MySQL `Connections` status variable. Number of all connection attempts (both successful and unsuccessful).
mysql_interactive_timeout	Seconds	Value of the MySQL `interactive_timeout` system variable. Time in seconds that the server waits for an interactive connection (one that connects with the mysql_real_connect() CLIENT_INTERACTIVE option) to become active before closing it.
mysql_max_connections	Number	Value of the MySQL `max_connections` system variable. The maximum number of simultaneous client connections.
mysql_max_used_connections	Number	Value of the MySQL `Max_used_connections` status variable. Max number of connections ever open at the same time.
mysql_pct_connections_aborted	Percentage	Aborted_connects / Connections * 100
mysql_pct_connections_used	Percentage	Threads_connected / max_connections * 100
mysql_threads_connected	None	Value of the MySQL `Threads_connected` status variable. Number of clients connected to the server. Is inaccurate when the thread pool is in use, since each client connection does not correspond to a dedicated thread in that case.
mysql_threads_running	None	Value of the MySQL `Threads_running` status variable. Number of client connections that are actively running a command, and not just sleeping while waiting to receive the next command to execute.
mysql_wait_timeout	Seconds	Value of the MySQL `wait_timeout` system variable. Time in seconds that the server waits for a connection to become active before closing it.

Credits, License

Authors: Linuxfabrik GmbH, Zurich
License: The Unlicense, see LICENSE file.
Credits:
- heavily inspired by MySQLTuner (https://github.com/major/MySQLTuner-perl)