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Check mysql-joins

Overview

Checks if many joins per day without indexes were executed on MySQL/MariaDB. Logic is taken from MySQLTuner script:mysql_stats(), v1.9.8.

Hints:

Fact Sheet

Fact Value
Check Plugin Download https://github.com/Linuxfabrik/monitoring-plugins/tree/main/check-plugins/mysql-joins
Check Interval Recommendation Once an hour
Can be called without parameters Yes
Compiled for Windows No
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-joins [-h] [-V] [--always-ok] [--defaults-file DEFAULTS_FILE]
                   [--defaults-group DEFAULTS_GROUP] [--timeout TIMEOUT]

Checks if many joins per day without indexes were executed 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
  --timeout TIMEOUT     Network timeout in seconds. Default: 3 (seconds)

Usage Examples

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

Output:

143.9K JOINs without indexes while MySQL/MariaDB is 1W 6D up (approx. 10.9K joins without indexes per day) 

Recommendations:
* Use JOIN with indexes
* Otherwise set join_buffer_size > 4.0MiB

States

  • WARN if there are more than 250 joins without indexes per day.

Perfdata / Metrics

Name Type Description
mysql_join_buffer_size Bytes Minimum size in bytes of the buffer used for queries that cannot use an index, and instead perform a full table scan. Increase to get faster full joins when adding indexes is not possible, although be aware of memory issues, since joins will always allocate the minimum size.
mysql_select_full_join Continous Counter Number of joins which did not use an index. If not zero, you may need to check table indexes.
mysql_select_range_check Continous Counter Number of joins without keys that check for key usage after each row. If not zero, you may need to check table indexes.
mysql_uptime Seconds Number of seconds the server has been running.
mysql_joins_without_indexes Continous Counter Select_range_check + Select_full_join
mysql_joins_without_indexes_per_day Number joins_without_indexes / Uptime in days

Credits, License