聊聊MySQL中的参数

# 参数查询
show global variables like 'var_name'; //查看全局系统变量的值，可使用%通配符
show session variables like 'var_name'; //查看会话系统变量的值
show  variables like 'var_name'; //优先返回会话系统变量，若会话系统变量不存在，则返回全局系统变量。

# 也可用select查询某个特定参数
select @@global.var_name; //全局系统变量
select @@session.var_name; //会话系统变量
select @@var_name; //优先会话系统变量

# 查询示例
mysql> show global variables like 'server_id';
+---------------+---------+
| Variable_name | Value |
+---------------+---------+
| server_id | 1003306 |
+---------------+---------+
1 row in set (0.00 sec)

mysql> show global variables like 'log_bin%';
+---------------------------------+-------------------------------+
| Variable_name   | Value    |
+---------------------------------+-------------------------------+
| log_bin    | ON    |
| log_bin_basename  | /data/mysql/logs/binlog |
| log_bin_index   | /data/mysql/logs/binlog.index |
| log_bin_trust_function_creators | ON    |
| log_bin_use_v1_row_events | OFF    |
+---------------------------------+-------------------------------+
5 rows in set (0.00 sec)

mysql> select @@server_id;
+-------------+
| @@server_id |
+-------------+
| 1003306 |
+-------------+
1 row in set (0.00 sec)

# 动态修改参数
set global var_name = value;
set session var_name = value;
set var_name = value;

set @@global.var_name = value;
set @@session.var_name = value;
set @@var_name = value;

# 参数修改示例
mysql> set global sort_buffer_size = 2097152;
Query OK, 0 rows affected (0.00 sec)

mysql> set session sort_buffer_size = 4194304;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@global.sort_buffer_size,@@session.sort_buffer_size;
+---------------------------+----------------------------+
| @@global.sort_buffer_size | @@session.sort_buffer_size |
+---------------------------+----------------------------+
|   2097152 |   4194304 |
+---------------------------+----------------------------+
1 row in set (0.00 sec)

vi /etc/my.cnf
# 简单模板如下：
[mysqld]
user = mysql 
datadir = /data/mysql/data  
socket = /data/mysql/tmp/mysql.sock
pid-file = /data/mysql/tmp/mysqld.pid 
skip_name_resolve = 1
max_connections = 2000
lower_case_table_names = 1
log_timestamps=SYSTEM
max_allowed_packet = 32M
...