设置Mysql sort_buffer_size参数

按照官网的解释:
Each session that must perform a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. At minimum the sort_buffer_size value must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value of max_sort_length may require increasing the value of sort_buffer_size. For more information, see Section 8.2.1.14, “ORDER BY Optimization”

sort_buffer_size 是一个connection级参数，在每个connection需要buffer的时候，一次性分配的内存。
sort_buffer_size 并不是越大越好，过大的设置+高并发可能会耗尽系统内存资源。

1.查看sort_buffer_size默认值，默认值为256K

mysql> show variables like 'sort_buffer_size';
+------------------+--------+
| Variable_name    | Value  |
+------------------+--------+
| sort_buffer_size | 262144 |
+------------------+--------+
1 row in set (0.00 sec)

2.设置global级别的sort_buffer_size值，设置sort_buffer_size=1M

mysql> SET GLOBAL sort_buffer_size = 1024*1024;
Query OK, 0 rows affected (0.00 sec)

3.设置session级别的sort_buffer_size值，设置sort_buffer_size=2M

mysql> SET session sort_buffer_size = 2*1024*1024;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show variables like 'sort_buffer_size';
+------------------+---------+
| Variable_name    | Value   |
+------------------+---------+
| sort_buffer_size | 2097152 |
+------------------+---------+
1 row in set (0.00 sec)

4.设置永久生效，需要修改/etc/my.cnf文件，重启Mysql后生效

[mysqld]
# 固定Mysql sort_buffer_size参数
sort_buffer_size=1M
# 设置3306端口
port=3306
# 设置mysql的安装目录
basedir=D:\mysql-8.0.25-winx64  # 切记此处一定要用双斜杠\\，单斜杠我这里会出错
# 设置mysql数据库的数据的存放目录
datadir=D:\mysql-8.0.25-winx64\\data   # data目录之后初始化会自动创建
# 允许最大连接数
max_connections=200
# 允许连接失败的次数。这是为了防止有人从该主机试图攻击数据库系统
max_connect_errors=10
# 服务端使用的字符集默认为UTF8
character-set-server=utf8mb4
# 创建新表时将使用的默认存储引擎
default-storage-engine=INNODB
# 默认使用“mysql_native_password”插件认证
default_authentication_plugin=mysql_native_password
[mysql]
# 设置mysql客户端默认字符集
default-character-set=utf8mb4
[client]
# 设置mysql客户端连接服务端时默认使用的端口
port=3306
default-character-set=utf8mb4