mysql如何更改Querycache系统缓存
调整MYSQL服务器的系统变量
mysqld服务器维护两种变量。全局变量影响服务器的全局操作。会话变量影响具体客户端连接相关操作。服务器启动时，将所有全局变量初始化为默认值。可以在选项文件或命令行中指定的选项来更改这些默认值。服务器启动后，通过连接服务器并执行SET GLOBAL var_name语句可以更改动态全局变量。要想更改全局变量，必须具有SUPER权限。
方法一：
mysql> SHOW VARIABLES LIKE 'query_cache_size';
+------------------+----------+
| Variable_name | Value |
+------------------+----------+
| query_cache_size | 23068672 |
+------------------+----------+
1 row in set (0.01 sec)
mysql> SET GLOBAL query_cache_size = 31457280;
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW VARIABLES LIKE 'query_cache_size';
+------------------+----------+
| Variable_name | Value |
+------------------+----------+
| query_cache_size | 31457280 |
+------------------+----------+
1 row in set (0.00 sec)
方法二：
mysql> show variables like 'query_cache_size%';
+------------------+----------+
| Variable_name | Value |
+------------------+----------+
| query_cache_size | 31457280 |
+------------------+----------+
1 row in set (0.00 sec)
mysql> SET @@global.query_cache_size = 20971520;
Query OK, 0 rows affected (0.09 sec)
mysql> show variables like 'query_cache_size%';
+------------------+----------+
| Variable_name | Value |
+------------------+----------+
| query_cache_size | 20971520 |
+------------------+----------+
1 row in set (0.00 sec)
mysql> select @@query_cache_size;
+--------------------+
| @@query_cache_size |
+--------------------+
| 20971520 |
+--------------------+
1 row in set (0.06 sec)
