MySQL的variables和status

VARIABLES

在文档中的位置：

MySQL Server Administration ----->   The MySQL Server ---->   Server System Variables

variables按作用域可以分为三种：

----  GLOBAL

----  SESSION

----  GLOBAL | SESSION

在informance_schema库中，有两张表 GLOBAL_VARIABLES 和 SESSION_VARIABLES 记录variable的名字和值。                        

GLOBAL类型的variable，如果是dynamic的，修改的时候需要使用set global命令，修改之后立即对所有session生效。

SESSION类型的variable，如果是dynamic的，修改的时候使用set命令，修改之后只对当前session立即生效，不会影响global和其他session。

GLOBAL | SESSION的variable，修改的时候使用set global或者set命令。

                                                           使用set global命令， 对当前已连接的session不生效，只对新建立的连接生效。

                                                           使用set命令，只对当前session生效，对已存在的其他连接和新建的连接无影响。

以如下两个variable为例：

sort_buffer_size作用域为global | session

Command-Line Format	--sort_buffer_size=#
System Variable	Name	sort_buffer_size
	Variable Scope	Global, Session
	Dynamic Variable	Yes

query_cache_size的作用域为global

Command-Line Format	--query_cache_size=#
System Variable	Name	query_cache_size
	Variable Scope	Global
	Dynamic Variable	Yes

mysql> use information_schema
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables like '%VARIABLE%';
+-------------------------------------------+
| Tables_in_information_schema (%VARIABLE%) |
+-------------------------------------------+
| GLOBAL_VARIABLES                          |
| SESSION_VARIABLES                         |
+-------------------------------------------+
2 rows in set (0.00 sec)

mysql> desc GLOBAL_VARIABLES;
+----------------+---------------+------+-----+---------+-------+
| Field          | Type          | Null | Key | Default | Extra |
+----------------+---------------+------+-----+---------+-------+
| VARIABLE_NAME  | varchar(64)   | NO   |     |         |       |
| VARIABLE_VALUE | varchar(1024) | YES  |     | NULL    |       |
+----------------+---------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

mysql> show variables like '%innodb_buffer_pool_size%';
+-------------------------+-----------+
| Variable_name           | Value     |
+-------------------------+-----------+
| innodb_buffer_pool_size | 134217728 |
+-------------------------+-----------+
1 row in set (0.00 sec)

mysql> set global innodb_buffer_pool_size=104857600;
ERROR 1238 (HY000): Variable 'innodb_buffer_pool_size' is a <span style="background-color: rgb(255, 0, 0);">read only variable</span>

mysql> show variables like '%sort_buffer%';
+-------------------------+---------+
| Variable_name           | Value   |
+-------------------------+---------+
| innodb_sort_buffer_size | 1048576 |
| myisam_sort_buffer_size | 8388608 |
| sort_buffer_size        | 262144  |
+-------------------------+---------+
3 rows in set (0.00 sec)

mysql> set global sort_buffer_size=1048576;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%sort_buffer%';
+-------------------------+---------+
| Variable_name           | Value   |
+-------------------------+---------+
| innodb_sort_buffer_size | 1048576 |
| myisam_sort_buffer_size | 8388608 |
| sort_buffer_size        | 262144  |
+-------------------------+---------+
3 rows in set (0.00 sec)

mysql> exit
Bye
[root@mysqlrep2 ~]# /usr/local/mysql/bin/mysql -uroot -p -S /dbdata/data/mysql.sock 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.6.27 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%sort_buffer%';
+-------------------------+---------+
| Variable_name           | Value   |
+-------------------------+---------+
| innodb_sort_buffer_size | 1048576 |
| myisam_sort_buffer_size | 8388608 |
| sort_buffer_size        | 1048576 |
+-------------------------+---------+
3 rows in set (0.00 sec)

mysql> set sort_buffer_size=1000000;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%sort_buffer%';
+-------------------------+---------+
| Variable_name           | Value   |
+-------------------------+---------+
| innodb_sort_buffer_size | 1048576 |
| myisam_sort_buffer_size | 8388608 |
| sort_buffer_size        | 1000000 |
+-------------------------+---------+
3 rows in set (0.00 sec)

mysql> 
mysql> 
mysql> exit
Bye
[root@mysqlrep2 ~]# /usr/local/mysql/bin/mysql -uroot -p -S /dbdata/data/mysql.sock 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.27 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%sort_buffer%';
+-------------------------+---------+
| Variable_name           | Value   |
+-------------------------+---------+
| innodb_sort_buffer_size | 1048576 |
| myisam_sort_buffer_size | 8388608 |
| sort_buffer_size        | 1048576 |
+-------------------------+---------+
3 rows in set (0.00 sec)

mysql> 
mysql> 

mysql> 
mysql> show variables like '%query_cache_size%';
+------------------+---------+
| Variable_name    | Value   |
+------------------+---------+
| query_cache_size | 1048576 |
+------------------+---------+
1 row in set (0.00 sec)

mysql> set query_cache_size=1000000;
ERROR 1229 (HY000): Variable 'query_cache_size' is a <span style="background-color: rgb(255, 0, 0);">GLOBAL variable</span> and should be set with SET GLOBAL

mysql> set global query_cache_size=10485760;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%query_cache_size%';
+------------------+----------+
| Variable_name    | Value    |
+------------------+----------+
| query_cache_size | 10485760 |
+------------------+----------+
1 row in set (0.00 sec)

mysql> exit
Bye
[root@mysqlrep2 ~]# /usr/local/mysql/bin/mysql -uroot -p -S /dbdata/data/mysql.sock 
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.6.27 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show variables like '%query_cache_size%';
+------------------+----------+
| Variable_name    | Value    |
+------------------+----------+
| query_cache_size | 10485760 |
+------------------+----------+
1 row in set (0.00 sec)

STATUS

在文档中的位置：

MySQL Server Administration ----->   The MySQL Server ---->   Server Status Variables

status是数据库运行状态的记录或统计

如Bytes_received，Bytes_sent。

com_xxx 记录的是数据库运行的命令的统计，比如Com_delete是运行的delete命令的次数统计，类似的还有Com_drop_index等。

ststus按作用域可以分为三种：

----  GLOBAL          只在global级别进行统计

----  SESSION        只在session级别进行统计

----  GLOBAL | SESSION  在global和session级别都统计

flush status 清空当前session的统计，但对global的无影响。做统计或优化时有用。

Many status variables are reset to 0 by the FLUSH STATUS statement.

以Com_show_status

Com_show_status

integer

GLOBAL | SESSION

当前系统总的统计是10次

mysql> show global status;
+-----------------------------------------------+-------------+
| Variable_name                                 | Value       |
+-----------------------------------------------+-------------+
............
| Com_show_slave_status                         | 0           |
| Com_show_status                               | 10          |
| Com_show_storage_engines                      | 0           |
............
+-----------------------------------------------+-------------+
341 rows in set (0.00 sec)

mysql> 

当前session运行了3次

mysql> show status;
+-----------------------------------------------+-------------+
| Variable_name                                 | Value       |
+-----------------------------------------------+-------------+
............
| Com_show_slave_status                         | 0           |
| Com_show_status                               | 3           |
| Com_show_storage_engines                      | 0           |
............
+-----------------------------------------------+-------------+
341 rows in set (0.00 sec)

把当前session的统计清0

系统统计的总的次数不受影响

mysql> flush status;
Query OK, 0 rows affected (0.00 sec)

mysql> show global status;
+-----------------------------------------------+-------------+
| Variable_name                                 | Value       |
+-----------------------------------------------+-------------+
............       |
| Com_show_slave_status                         | 0           |
| Com_show_status                               | 12          |
| Com_show_storage_engines                      | 0           |
............
+-----------------------------------------------+-------------+
341 rows in set (0.00 sec)

mysql> 

当前session重新统计

mysql> show status;
+-----------------------------------------------+-------------+
| Variable_name                                 | Value       |
+-----------------------------------------------+-------------+
............
| Com_show_slave_status                         | 0           |
| Com_show_status                               | 2           |
| Com_show_storage_engines                      | 0           |
............
+-----------------------------------------------+-------------+
341 rows in set (0.00 sec)

mysql>