table_open_cache
WARNING
Rule IDs: tc_001
Overview
- Purpose
- Documented in the MySQL 8.4 manual as a server system variable (scope: Global). Purpose and semantics are described at the linked manual page.
- Dynamic (MySQL 8.4 reference)
- MySQL 8.4 marks this variable as dynamic (
Dynamic= Yes). Runtime changes useSET GLOBAL(global scope) orSET SESSION(session scope) — confirm syntax and persistence (SET PERSIST) in the manual. - Default value
- 4000 (MySQL 8.4)
- Version and product notes
- MariaDB and Percona Server may use different names, defaults, or dynamic behavior; verify their documentation.
- Documentation
- https://dev.mysql.com/doc/refman/8.4/en/server-system-variables.html#sysvar_table_open_cache
- Other vendors
What is checked
Rules that reference this variable, with their severity and what each rule detects:
- WARNING
tc_001: Increase table_open_cache. A high Opened_tables rate means MySQL frequently closes and reopens tables, adding overhead.
Tuning guidance
- Recommended actions:
- Increase table_open_cache. A high Opened_tables rate means MySQL frequently closes and reopens tables, adding overhead.
- Trade-offs: A larger table cache reduces file-open overhead but consumes file descriptors and memory. Size it relative to the number of tables accessed concurrently, not the total table count.
Example
SET GLOBAL table_open_cache = 4000;
Always validate on a non-production instance first. Use SET PERSIST (MySQL 8.0+) for changes that should survive restarts.