The kernel of the operating system provides the fundamental components needed for the server to function. With Unix-based systems, there are sometimes optimizations to be made by changing various parameter values for optimizations for your specific configuration. Below are some of the most commonly used system tuning for a MySQL database on a CentOS/RHEL system.
Memory settings in /etc/sysctl.conf
Swapping is not ideal for databases and should be avoided as much as possible.
vm.swappiness = 10
Maximum percentage of active memory that can be dirty pages:
vm.dirty_background_ratio = 3
Maximum percentage of total memory that can have dirty pages:
vm.dirty_ratio = 40
How long to keep data in page cache before expiring:
vm.dirty_expire_centisecs = 500
How often pdflush activates to clean dirty pages in hundredths of a seconds:
vm.dirty_writeback_centisecs = 100
Recommended minimum settings for semaphores:
kernel.sem = 250 32000 100 128
- The first value, SEMMSL, is the maximum number of semaphores per semaphore set - The second value, SEMMNS, defines the total number of semaphores for the system - The third value, SEMOPM, defines the maximum number of semaphore operations per semaphore call - The last value, SEMMNI, defines the number of entire semaphore sets for the system
Open file descriptors for MySQL:
#[domain] [type] [item] [value] mysql hard nofile 10000
The default CFQ I/O scheduler is appropriate for most workloads, but does not offer optimal performance for database environments.
- The deadline scheduler is recommended for physical systems
- The noop scheduler is recommended for virtual systems
innodb_buffer_pool_size - If you use Innodb, 70% to 80% of main memory is adequate. key_buffer_size - If you use MyISAM, approx 30% of main memory is adequate. sort_buffer_size - 256KB to 1MB read_buffer_size - 128KB to 512KB read_rnd_buffer_size - 256KB to 1MB