mysql系统变量_MySQL 系统变量(system variables)
3、全局與會話級別設置示例
--如何設置隔離級別
mysql> help isolation
Name: 'ISOLATION'
Description:
Syntax:
SET [GLOBAL | SESSION] TRANSACTION ISOLATION LEVEL
{
REPEATABLE READ
| READ COMMITTED
| READ UNCOMMITTED
| SERIALIZABLE
}
--下面我們通過演示隔離級別來設置全局與session級別變量
--查看當前session級別的隔離方式
root@localhost[(none)]> show variables like '%isolation%';
+---------------+-----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+-----------------+
| tx_isolation? | REPEATABLE-READ |
+---------------+-----------------+
--修改當前session級別的隔離方式為READ-COMMITTED
root@localhost[(none)]> set session transaction isolation level read committed;
root@localhost[(none)]> show variables like '%isolation%';
+---------------+----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+----------------+
| tx_isolation? | READ-COMMITTED |
+---------------+----------------+
--另外的一個session ， 登錄用戶為fred
--當前sessioin級別繼承全局隔離級別為REPEATABLE-READ
fred@localhost[(none)]> show variables like '%isolation%';
+---------------+-----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+-----------------+
| tx_isolation? | REPEATABLE-READ |
+---------------+-----------------+
--在root會話中設置全局隔離級別為serializable
root@localhost[(none)]> set global transaction isolation level serializable;
--注意，在root會話中 session級別還是為READ-COMMITTED
root@localhost[(none)]> show variables like '%isolation%';
+---------------+----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+----------------+
| tx_isolation? | READ-COMMITTED |
+---------------+----------------+
--在root會話中我可以看到全局的值已經變為SERIALIZABLE
root@localhost[(none)]> show global variables like '%isolation%';
+---------------+--------------+
| Variable_name | Value? ? ? ? |
+---------------+--------------+
| tx_isolation? | SERIALIZABLE |
+---------------+--------------+
--在fred中全局的也變成了SERIALIZABLE
fred@localhost[(none)]> show global variables like '%isolation%';
+---------------+--------------+
| Variable_name | Value? ? ? ? |
+---------------+--------------+
| tx_isolation? | SERIALIZABLE |
+---------------+--------------+
--從上面的演示來說，無論global級別如何設置，不會影響到當前session級別的設置
--下面我們使用一個新用戶登錄來看看全局設置是否影響新會話
robin@SZDB:~> mysql -urobin
--如下查詢新會話的隔離級別等于全局的隔離級別
robin@localhost[(none)]> show variables like '%isolation%';
+---------------+--------------+
| Variable_name | Value? ? ? ? |
+---------------+--------------+
| tx_isolation? | SERIALIZABLE |
+---------------+--------------+
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