performance_schema
WARNING
Rule IDs: lg_006
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 not dynamic (
Dynamic= No). It must be set inmy.cnfor on the command line; changing it requires a restart. - Default value
- ON (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/performance-schema-system-variables.html#sysvar_performance_schema
- Other vendors
What is checked
Rules that reference this variable, with their severity and what each rule detects:
- WARNING
lg_006: Enable performance_schema=ON. The overhead is generally low (1-5%) and the diagnostic value is immense.
Tuning guidance
- Recommended actions:
- Enable performance_schema=ON. The overhead is generally low (1-5%) and the diagnostic value is immense.
- Trade-offs: Enabling slow query log and performance_schema adds observability but consumes some I/O and CPU. General log should never be enabled in production due to extreme I/O overhead.
Example
-- In my.cnf (requires restart):
performance_schema = ON
Always validate on a non-production instance first. Use SET PERSIST (MySQL 8.0+) for changes that should survive restarts.