Configuration·MySQL
MySQL Server Variables
Some variables change on a running server, some need a restart, and some cannot change at all. `SET GLOBAL` tells you which is which - and a restart shows what it did not save.
Configuration Guide 12 of 45 Intermediate
- OSUbuntu 26.04 LTS (resolute)
- MySQL8.4.10-0ubuntu0.26.04.1
- EngineInnoDB (default)
- TimeAbout 14 min
- Reviewed27 August 2026
Written against the versions above. `innodb_buffer_pool_size` became dynamic in 5.7. On older servers it is one of the read-only settings, which is why so much older advice says a restart is required.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| db-a01 | 192.168.0.81 | Ubuntu 26.04 LTS | Primary / Source / Replica Set Member 1 | 2 Core | 4 GB | 50 GB |
Before you start
- MySQL running on db-a01, and
sudo mysqlaccess.
-
Change a value on the running server
-
Change one that costs real work
-
Try one that cannot change
-
Restart, and watch the change vanish