The MySQL server, mysqld, has many command options and system variables that can be set at startup to configure its operation. To determine the default command option and system variable values used by the server, execute this command:
shell> mysqld --verbose --help
The command produces a list of all mysqld options and configurable system variables. Its output includes the default option and variable values and looks something like this:
allow-suspicious-udfs FALSE archive ON auto-increment-increment 1 auto-increment-offset 1 autocommit TRUE automatic-sp-privileges TRUE back-log 50 basedir /home/jon/bin/mysql-5.5/ ... tmpdir /tmp transaction-alloc-block-size 8192 transaction-isolation REPEATABLE-READ transaction-prealloc-size 4096 updatable-views-with-limit YES verbose TRUE wait-timeout 28800
To see the current system variable values actually used by the server as it runs, connect to it and execute this statement:
mysql> SHOW VARIABLES;
To see some statistical and status indicators for a running server, execute this statement:
mysql> SHOW STATUS;
System variable and status information also is available using the mysqladmin command:
shell> mysqladmin variables shell> mysqladmin extended-status
For a full description of all command options, system variables, and status variables, see these sections:
More detailed monitoring information is available from the Performance Schema; see Chapter 22, MySQL Performance Schema.
MySQL uses algorithms that are very scalable, so you can usually run with very little memory. However, normally better performance results from giving MySQL more memory.
When tuning a MySQL server, the two most important variables to
table_open_cache. You should
first feel confident that you have these set appropriately before
trying to change any other variables.
The following examples indicate some typical variable values for different runtime configurations.
If you have at least 1-2GB of memory and many tables and want maximum performance with a moderate number of clients, use something like this:
shell> mysqld_safe --key_buffer_size=384M --table_open_cache=4000 \ --sort_buffer_size=4M --read_buffer_size=1M &
If you have only 256MB of memory and only a few tables, but you still do a lot of sorting, you can use something like this:
shell> mysqld_safe --key_buffer_size=64M --sort_buffer_size=1M
If there are very many simultaneous connections, swapping problems may occur unless mysqld has been configured to use very little memory for each connection. mysqld performs better if you have enough memory for all connections.
With little memory and lots of connections, use something like this:
shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=100K \ --read_buffer_size=100K &
Or even this:
shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=16K \ --table_open_cache=32 --read_buffer_size=8K \ --net_buffer_length=1K &
If you are performing
GROUP BY or
ORDER BY operations on tables that are much
larger than your available memory, increase the value of
read_rnd_buffer_size to speed up
the reading of rows following sorting operations.
You can make use of the example option files included with your MySQL distribution; see Section 5.1.2, “Server Configuration Defaults”.
If you specify an option on the command line for mysqld or mysqld_safe, it remains in effect only for that invocation of the server. To use the option every time the server runs, put it in an option file. See Section 4.2.6, “Using Option Files”.