Check mysql-table-definition-cache¶

Overview¶

Checks the table definition cache size in MySQL/MariaDB. A cache that is too small to hold definitions for all tables causes repeated disk reads. Logic is taken from MySQLTuner script:mysql_stats(), v1.9.8.

Important Notes:

Requires MySQL/MariaDB v5.1+
See additional notes for all mysql monitoring plugins
User account requires access to INFORMATION_SCHEMA (user with no privileges is sufficient) and SELECT privileges on all schemas and tables to provide accurate results
For most INFORMATION_SCHEMA tables, each MySQL user has the right to access them, but can see only the rows in the tables that correspond to objects for which the user has the proper access privileges. So you can’t grant permission to INFORMATION_SCHEMA directly, you have to grant SELECT permission to the tables on your own schemas, and as you do, those tables will start showing up in INFORMATION_SCHEMA queries.

Data Collection:

Queries SHOW GLOBAL VARIABLES for table_definition_cache
Counts total tables via SELECT COUNT(*) FROM information_schema.tables

Fact Sheet¶

Fact	Value
Check Plugin Download	https://github.com/Linuxfabrik/monitoring-plugins/tree/main/check-plugins/mysql-table-definition-cache
Nagios/Icinga Check Name	`check_mysql_table_definition_cache`
Check Interval Recommendation	Every hour
Can be called without parameters	Yes
Runs on	Cross-platform
Compiled for Windows	No
3rd Party Python modules	`pymysql`

Help¶

usage: mysql-table-definition-cache [-h] [-V] [--always-ok]
                                    [--defaults-file DEFAULTS_FILE]
                                    [--defaults-group DEFAULTS_GROUP]
                                    [--timeout TIMEOUT]

Checks the table definition cache size in MySQL/MariaDB. Alerts if the cache
is too small to hold definitions for all tables, causing repeated disk reads.

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
                        MySQL/MariaDB cnf file to read parameters like user,
                        host and password from (instead of specifying them on
                        the command line). 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-table-definition-cache --defaults-file=/var/spool/icinga2/.my.cnf

Output:

table_definition_cache (400) is lower than number of tables (516) [WARNING]. Set table_definition_cache > 516 or to -1 (autosizing if supported).

States¶

OK if table_definition_cache is large enough to hold all table definitions, or set to -1 (autosizing).
WARN if the number of table definitions that can be cached is less than the total number of tables.
--always-ok suppresses all alerts and always returns OK.

Perfdata / Metrics¶

Name	Type	Description
mysql_table_definition_cache	Number	Number of table definitions that can be cached.
mysql_total_tables	Number	Total number of tables.

Credits, License¶

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