MySQL 参数文件及参数

MySQL的参数文件为----my.cnf

1. 如何确定数据库读取的哪一个，命令给出了答案

   [[email protected] home]# mysql --help |grep my.cnf
                         order of preference, my.cnf, $MYSQL_TCP_PORT,
   /etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf
   [[email protected] home]#

2. 参数有的是为客户端准备，有的是为服务器准备

   [[email protected] home]# cat /etc/my.cnf | grep -v "^#"

   [client]

   port=3306

   [mysqld]
   datadir=/opt/mysql/data

   basedir = /usr/local/mysql
   socket=/usr/local/mysql/mysql.sock
   user=mysql
   character_set_server=utf8
   server_id = 12
   join_buffer_size = 128M
   sort_buffer_size = 2M
   pid-file=/opt/mysql/data/mysqld.pid
   [[email protected] home]#

3. 什么是参数？

   这个就好比是键跟值得关系 如read_buffer_size=12M read_buffer_size就是键 12M就是指

   分为两类动态和静态的（只读），也可以分成是全局和局部的，动态的可以修改但是只会在mysql server的整个生命周期中起作用，下次重启之后会重新根据参数配置文件加载，所以要想永久生效还是修改配置文件，局部只对当前session有效，全局的对所有重新上来的会话有效，动态修改参数使用set [global] variables=key。

4. 查看参数

   可以使用show variables like "variables_name" select @@session.variables_name select @@global.variables_name

   如查看read_buffer_size

   mysql> set read_buffer_size=524288;
   Query OK, 0 rows affected (0.07 sec)

   mysql> select @@session.read_buffer_size;
   +----------------------------+
   | @@session.read_buffer_size |
   +----------------------------+
   |                     524288 |
   +----------------------------+
   1 row in set (0.00 sec)

   mysql> select @@global.read_buffer_size;
   +---------------------------+
   | @@global.read_buffer_size |
   +---------------------------+
   |                    131072 |
   +---------------------------+
   1 row in set (0.00 sec)

   mysql> show variables like "read_buffer_size%";
   +------------------+--------+
   | Variable_name    | Value  |
   +------------------+--------+
   | read_buffer_size | 524288 |
   +------------------+--------+
   1 row in set (0.00 sec)

   可以看到同样设置了read_buffer_size但是session和global却不一样 因为我设置的时候没有加global

5. 如果更改静态参数会有什么结果呢

   mysql> set global datadir=‘/opt‘;
   ERROR 1238 (HY000): Variable ‘datadir‘ is a read only variable
   mysql>