thread_cache_size
INFO
Rule IDs: cn_003
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
- auto-sized (8 + max_connections/100) (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_thread_cache_size
- Other vendors
What is checked
Rules that reference this variable, with their severity and what each rule detects:
- INFO
cn_003: Increase thread_cache_size to reduce thread creation overhead. Aim for Threads_created/Connections < 1-2%.
Tuning guidance
- Recommended actions:
- Increase thread_cache_size to reduce thread creation overhead. Aim for Threads_created/Connections < 1-2%.
- Trade-offs: Validate recommendations against monitoring, workload profiles, and vendor documentation before making changes.
Example
SET GLOBAL thread_cache_size = 16;
Always validate on a non-production instance first. Use SET PERSIST (MySQL 8.0+) for changes that should survive restarts.