MySQL全局变量设置的实现

[mysqld]
max_connections = 500
query_cache_size = 128M

sudo systemctl restart mysql   # 对于系统使用 systemd
sudo service mysql restart     # 对于使用 sysvinit 或 upstart

SET GLOBAL max_connections = 500;

SHOW VARIABLES LIKE 'max_connections';

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.23</version>
</dependency>

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class MySQLGlobalVariableExample {

    private static final String JDBC_URL = "jdbc:mysql://localhost:3306/your_database";
    private static final String USER = "your_db_user";
    private static final String PASSWORD = "your_db_password";

    public static void main(String[] args) {
        try (Connection connection = DriverManager.getConnection(JDBC_URL, USER, PASSWORD);
             Statement statement = connection.createStatement()) {

            // 动态设置全局变量
            String setMaxConnections = "SET GLOBAL max_connections = 500";
            statement.execute(setMaxConnections);
            System.out.println("Set max_connections to 500");

            // 查询全局变量
            String queryMaxConnections = "SHOW VARIABLES LIKE 'max_connections'";
            try (ResultSet resultSet = statement.executeQuery(queryMaxConnections)) {
                while (resultSet.next()) {
                    String variableName = resultSet.getString("Variable_name");
                    String value = resultSet.getString("Value");
                    System.out.printf("%s: %s\n", variableName, value);
                }
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}