Documentation Home
MySQL 5.7 Reference Manual
Related Documentation Download this Manual
PDF (US Ltr) - 35.4Mb
PDF (A4) - 35.5Mb
PDF (RPM) - 33.8Mb
EPUB - 8.6Mb
HTML Download (TGZ) - 8.4Mb
HTML Download (Zip) - 8.5Mb
HTML Download (RPM) - 7.3Mb
Eclipse Doc Plugin (TGZ) - 9.3Mb
Eclipse Doc Plugin (Zip) - 11.3Mb
Man Pages (TGZ) - 198.3Kb
Man Pages (Zip) - 302.3Kb
Info (Gzip) - 3.2Mb
Info (Zip) - 3.2Mb
Excerpts from this Manual

MySQL 5.7 Reference Manual  /  ...  /  Tuning Server Parameters

9.12.2 Tuning Server Parameters

You can determine the default buffer sizes used by the mysqld server using this command:

shell> mysqld --verbose --help

This command produces a list of all mysqld options and configurable system variables. The output includes the default variable values and looks something like this:

abort-slave-event-count                                      0
allow-suspicious-udfs                                        FALSE
archive                                                      ON
auto-increment-increment                                     1
auto-increment-offset                                        1
autocommit                                                   TRUE
automatic-sp-privileges                                      TRUE
avoid-temporal-upgrade                                       FALSE
back-log                                                     80
basedir                                                      /home/jon/bin/mysql-5.7/
...
tmpdir                                                       /tmp
transaction-alloc-block-size                                 8192
transaction-isolation                                        REPEATABLE-READ
transaction-prealloc-size                                    4096
transaction-read-only                                        FALSE
transaction-write-set-extraction                             OFF
updatable-views-with-limit                                   YES
validate-user-plugins                                        TRUE
verbose                                                      TRUE
wait-timeout

For a mysqld server that is currently running, you can see the current values of its system variables by connecting to it and issuing this statement:

mysql> SHOW VARIABLES;

You can also see some statistical and status indicators for a running server by issuing this statement:

mysql> SHOW STATUS;

System variable and status information also can be obtained using mysqladmin:

shell> mysqladmin variables
shell> mysqladmin extended-status

For a full description of all system and status variables, see Section 6.1.4, “Server System Variables”, and Section 6.1.6, “Server Status Variables”.

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 configure are key_buffer_size and 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 6.1.2, “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.

To see the effects of a parameter change, do something like this:

shell> mysqld --key_buffer_size=128M --verbose --help

The variable values are listed near the end of the output. Make sure that the --verbose and --help options are last. Otherwise, the effect of any options listed after them on the command line are not reflected in the output.

For information on optimizing the InnoDB storage engine performance, see Section 9.5, “Optimizing for InnoDB Tables”.


User Comments
Sign Up Login You must be logged in to post a comment.