innodb_adaptive_hash_index
INFO
Rule IDs: mi_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
- 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/innodb-parameters.html#sysvar_innodb_adaptive_hash_index
- Other vendors
What is checked
Rules that reference this variable, with their severity and what each rule detects:
- INFO
mi_003: If adaptive hash index searches are very low relative to btree searches, consider disabling innodb_adaptive_hash_index to reduce memory overhead and contention.
Tuning guidance
- Recommended actions:
- If adaptive hash index searches are very low relative to btree searches, consider disabling innodb_adaptive_hash_index to reduce memory overhead and contention.
- Trade-offs: Validate recommendations against monitoring, workload profiles, and vendor documentation before making changes.
Example
Consult the manual for whether SET GLOBAL, SET PERSIST, or SET SESSION applies.