mysql系统变量_MySQL 系统变量(system variables)
3、全局與會(huì)話級(jí)別設(shè)置示例
--如何設(shè)置隔離級(jí)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(jí)別來設(shè)置全局與session級(jí)別變量
--查看當(dāng)前session級(jí)別的隔離方式
root@localhost[(none)]> show variables like '%isolation%';
+---------------+-----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+-----------------+
| tx_isolation? | REPEATABLE-READ |
+---------------+-----------------+
--修改當(dāng)前session級(jí)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(gè)session ， 登錄用戶為fred
--當(dāng)前sessioin級(jí)別繼承全局隔離級(jí)別為REPEATABLE-READ
fred@localhost[(none)]> show variables like '%isolation%';
+---------------+-----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+-----------------+
| tx_isolation? | REPEATABLE-READ |
+---------------+-----------------+
--在root會(huì)話中設(shè)置全局隔離級(jí)別為serializable
root@localhost[(none)]> set global transaction isolation level serializable;
--注意，在root會(huì)話中 session級(jí)別還是為READ-COMMITTED
root@localhost[(none)]> show variables like '%isolation%';
+---------------+----------------+
| Variable_name | Value? ? ? ? ? |
+---------------+----------------+
| tx_isolation? | READ-COMMITTED |
+---------------+----------------+
--在root會(huì)話中我可以看到全局的值已經(jīng)變?yōu)镾ERIALIZABLE
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(jí)別如何設(shè)置，不會(huì)影響到當(dāng)前session級(jí)別的設(shè)置
--下面我們使用一個(gè)新用戶登錄來看看全局設(shè)置是否影響新會(huì)話
robin@SZDB:~> mysql -urobin
--如下查詢新會(huì)話的隔離級(jí)別等于全局的隔離級(jí)別
robin@localhost[(none)]> show variables like '%isolation%';
+---------------+--------------+
| Variable_name | Value? ? ? ? |
+---------------+--------------+
| tx_isolation? | SERIALIZABLE |
+---------------+--------------+
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