(mysql.info) program-variables
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4.3.4 Using Options to Set Program Variables
--------------------------------------------
Many MySQL programs have internal variables that can be set at runtime.
Program variables are set the same way as any other long option that
takes a value. For example, `mysql' has a `max_allowed_packet' variable
that controls the maximum size of its communication buffer. To set the
`max_allowed_packet' variable for `mysql' to a value of 16MB, use
either of the following commands:
shell> mysql --max_allowed_packet=16777216
shell> mysql --max_allowed_packet=16M
The first command specifies the value in bytes. The second specifies
the value in megabytes. For variables that take a numeric value, the
value can be given with a suffix of `K', `M', or `G' (either uppercase
or lowercase) to indicate a multiplier of 1024, 10242 or 10243. (For
example, when used to set `max_allowed_packet', the suffixes indicate
units of kilobytes, megabytes, or gigabygtes.)
In an option file, variable settings are given without the leading
dashes:
[mysql]
max_allowed_packet=16777216
Or:
[mysql]
max_allowed_packet=16M
If you like, underscores in a variable name can be specified as dashes.
The following option groups are equivalent. Both set the size of the
server's key buffer to 512MB:
[mysqld]
key_buffer_size=512M
[mysqld]
key-buffer-size=512M
* Before MySQL 4.0.2, the only syntax for setting program
variables was -set-variable=OPTION=VALUE (or set-variable=OPTION=VALUE
in option files). This syntax still is recognized, but is deprecated as
of MySQL 4.0.2.
Many server system variables can also be set at runtime. For details,
see dynamic-system-variables.
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