MySQL中事件调度器用法与使用场景详解

-- 查看事件调度器是否启用
SHOW VARIABLES LIKE 'event_scheduler';

-- 查看当前运行的事件
SHOW PROCESSLIST;

-- 方法1：动态启用（重启后失效）
SET GLOBAL event_scheduler = ON;

-- 方法2：在配置文件中永久启用
-- 在my.cnf或my.ini中添加：
-- [mysqld]
-- event_scheduler = ON

-- 应该显示 ON 或 1
SELECT @@event_scheduler;

-- 查看事件调度器进程
SHOW PROCESSLIST;
-- 应该能看到 "Daemon" 用户的 "event_scheduler" 进程

CREATE
    [DEFINER = user]
    EVENT
    [IF NOT EXISTS]
    event_name
    ON SCHEDULE schedule
    [ON COMPLETION [NOT] PRESERVE]
    [ENABLE | DISABLE | DISABLE ON SLAVE]
    [COMMENT 'string']
    DO
      event_body;

-- 在指定时间执行一次
ON SCHEDULE AT timestamp

-- 示例
ON SCHEDULE AT '2024-12-31 23:59:59'
ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 HOUR

-- 按间隔重复执行
ON SCHEDULE EVERY interval
[STARTS timestamp]
[ENDS timestamp]

-- 示例
ON SCHEDULE EVERY 1 DAY
ON SCHEDULE EVERY 1 HOUR STARTS '2024-01-01 00:00:00'
ON SCHEDULE EVERY 30 MINUTE STARTS NOW() ENDS '2024-12-31 23:59:59'

-- 创建每天凌晨2点清理30天前日志的事件
DELIMITER $$

CREATE EVENT IF NOT EXISTS cleanup_old_logs
ON SCHEDULE EVERY 1 DAY
STARTS '2024-01-01 02:00:00'
ON COMPLETION PRESERVE
ENABLE
COMMENT '每天清理30天前的日志数据'
DO
BEGIN
    -- 删除30天前的访问日志
    DELETE FROM access_logs 
    WHERE created_at < DATE_SUB(NOW(), INTERVAL 30 DAY);
    
    -- 删除30天前的错误日志
    DELETE FROM error_logs 
    WHERE created_at < DATE_SUB(NOW(), INTERVAL 30 DAY);
    
    -- 记录清理操作
    INSERT INTO maintenance_log (operation, executed_at, description)
    VALUES ('cleanup_old_logs', NOW(), 
            CONCAT('Cleaned logs older than ', DATE_SUB(NOW(), INTERVAL 30 DAY)));
END$$

DELIMITER ;

-- 创建每小时统计用户活跃度的事件
DELIMITER $$

CREATE EVENT hourly_user_stats
ON SCHEDULE EVERY 1 HOUR
ON COMPLETION PRESERVE
ENABLE
COMMENT '每小时统计用户活跃度'
DO
BEGIN
    DECLARE current_hour DATETIME;
    SET current_hour = DATE_FORMAT(NOW(), '%Y-%m-%d %H:00:00');
    
    -- 插入或更新用户活跃统计
    INSERT INTO user_activity_stats (hour, active_users, total_actions)
    SELECT 
        current_hour,
        COUNT(DISTINCT user_id) as active_users,
        COUNT(*) as total_actions
    FROM user_actions 
    WHERE created_at >= current_hour 
      AND created_at < DATE_ADD(current_hour, INTERVAL 1 HOUR)
    ON DUPLICATE KEY UPDATE
        active_users = VALUES(active_users),
        total_actions = VALUES(total_actions),
        updated_at = NOW();
END$$

DELIMITER ;

-- 创建每周日凌晨进行数据备份的事件
DELIMITER $$

CREATE EVENT weekly_backup
ON SCHEDULE EVERY 1 WEEK
STARTS '2024-01-07 03:00:00'  -- 从第一个周日开始
ON COMPLETION PRESERVE
ENABLE
COMMENT '每周数据备份'
DO
BEGIN
    -- 创建备份表
    SET @backup_table = CONCAT('user_data_backup_', DATE_FORMAT(NOW(), '%Y%m%d'));
    SET @sql = CONCAT('CREATE TABLE ', @backup_table, ' AS SELECT * FROM user_data');
    
    PREPARE stmt FROM @sql;
    EXECUTE stmt;
    DEALLOCATE PREPARE stmt;
    
    -- 记录备份操作
    INSERT INTO backup_log (backup_table, created_at, status)
    VALUES (@backup_table, NOW(), 'completed');
END$$

DELIMITER ;

-- 查看所有事件
SHOW EVENTS;

-- 查看特定数据库的事件
SHOW EVENTS FROM database_name;

-- 查看事件详细信息
SELECT * FROM information_schema.EVENTS 
WHERE EVENT_SCHEMA = 'your_database';

-- 查看特定事件的创建语句
SHOW CREATE EVENT event_name;

-- 修改事件调度
ALTER EVENT cleanup_old_logs
ON SCHEDULE EVERY 2 DAY;

-- 启用/禁用事件
ALTER EVENT cleanup_old_logs ENABLE;
ALTER EVENT cleanup_old_logs DISABLE;

-- 修改事件内容
ALTER EVENT cleanup_old_logs
DO
BEGIN
    DELETE FROM access_logs 
    WHERE created_at < DATE_SUB(NOW(), INTERVAL 60 DAY);
END;

-- 删除事件
DROP EVENT IF EXISTS cleanup_old_logs;

-- 定期清理临时数据
CREATE EVENT cleanup_temp_data
ON SCHEDULE EVERY 1 HOUR
DO
BEGIN
    DELETE FROM temp_sessions WHERE expires_at < NOW();
    DELETE FROM temp_files WHERE created_at < DATE_SUB(NOW(), INTERVAL 1 DAY);
END;

-- 定期收集性能指标
CREATE EVENT collect_performance_metrics
ON SCHEDULE EVERY 5 MINUTE
DO
BEGIN
    INSERT INTO performance_metrics (
        timestamp, 
        connections, 
        queries_per_second,
        slow_queries
    )
    SELECT 
        NOW(),
        (SELECT VARIABLE_VALUE FROM information_schema.GLOBAL_STATUS 
         WHERE VARIABLE_NAME = 'Threads_connected'),
        (SELECT VARIABLE_VALUE FROM information_schema.GLOBAL_STATUS 
         WHERE VARIABLE_NAME = 'Queries') / 300, -- 5分钟内的平均QPS
        (SELECT VARIABLE_VALUE FROM information_schema.GLOBAL_STATUS 
         WHERE VARIABLE_NAME = 'Slow_queries');
END;

-- 定期处理订单状态
CREATE EVENT process_pending_orders
ON SCHEDULE EVERY 10 MINUTE
DO
BEGIN
    -- 自动取消超时未支付订单
    UPDATE orders 
    SET status = 'cancelled', updated_at = NOW()
    WHERE status = 'pending' 
      AND created_at < DATE_SUB(NOW(), INTERVAL 30 MINUTE);
    
    -- 自动确认收货超时订单
    UPDATE orders 
    SET status = 'completed', updated_at = NOW()
    WHERE status = 'shipped' 
      AND shipped_at < DATE_SUB(NOW(), INTERVAL 7 DAY);
END;

-- 避免在高峰期执行重型任务
CREATE EVENT heavy_maintenance
ON SCHEDULE EVERY 1 DAY
STARTS '2024-01-01 02:00:00'  -- 选择业务低峰期
DO
BEGIN
    -- 分批处理大量数据
    DECLARE done INT DEFAULT FALSE;
    DECLARE batch_size INT DEFAULT 1000;
    
    REPEAT
        DELETE FROM large_table 
        WHERE condition 
        LIMIT batch_size;
        
        -- 检查是否还有数据需要处理
        SELECT ROW_COUNT() = 0 INTO done;
        
        -- 短暂休息，避免长时间锁表
        DO SLEEP(0.1);
    UNTIL done END REPEAT;
END;

-- 添加错误处理和日志记录
DELIMITER $$

CREATE EVENT robust_cleanup
ON SCHEDULE EVERY 1 DAY
DO
BEGIN
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        ROLLBACK;
        INSERT INTO event_error_log (event_name, error_time, error_message)
        VALUES ('robust_cleanup', NOW(), 'Event execution failed');
    END;
    
    START TRANSACTION;
    
    -- 执行清理操作
    DELETE FROM old_data WHERE created_at < DATE_SUB(NOW(), INTERVAL 30 DAY);
    
    -- 记录成功执行
    INSERT INTO event_execution_log (event_name, execution_time, status)
    VALUES ('robust_cleanup', NOW(), 'success');
    
    COMMIT;
END$$

DELIMITER ;

-- 查看事件调度器状态
SELECT 
    EVENT_SCHEMA,
    EVENT_NAME,
    STATUS,
    LAST_EXECUTED,
    NEXT_EXECUTION_TIME
FROM information_schema.EVENTS;

-- 查看事件执行历史（需要开启general_log）
SELECT * FROM mysql.general_log 
WHERE command_type = 'Query' 
  AND argument LIKE '%EVENT%'
ORDER BY event_time DESC;

-- 手动执行事件内容进行测试
-- 将事件内容复制出来单独执行

-- 创建测试事件（短间隔）
CREATE EVENT test_event
ON SCHEDULE EVERY 1 MINUTE
STARTS NOW()
ENDS DATE_ADD(NOW(), INTERVAL 5 MINUTE)
DO
BEGIN
    INSERT INTO test_log VALUES (NOW(), 'Event executed');
END;