MySQL中BLACKHOLE存储引擎的原理与应用场景介绍

-- 创建BLACKHOLE表示例
CREATE TABLE blackhole_demo (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(50),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE = BLACKHOLE;

-- 插入数据（数据将被"吞噬"）
INSERT INTO blackhole_demo (name) VALUES ('测试数据'), ('另一个测试');

-- 查询总是返回空集
SELECT * FROM blackhole_demo;
-- 结果：Empty set (0.00 sec)

-- 在主从架构中的典型应用
-- 主服务器配置
CREATE TABLE critical_data (
    id INT PRIMARY KEY,
    business_data TEXT
) ENGINE = InnoDB;

CREATE TABLE audit_logs (
    id INT PRIMARY KEY,
    log_message TEXT,
    log_time DATETIME
) ENGINE = BLACKHOLE;  -- 不复制到从服务器

CREATE TABLE operational_metrics (
    id INT PRIMARY KEY,
    metric_name VARCHAR(100),
    metric_value DECIMAL(10,2)
) ENGINE = BLACKHOLE;  -- 仅在主服务器记录，不复制

-- 性能对比测试脚本
DELIMITER $$

CREATE PROCEDURE performance_benchmark()
BEGIN
    DECLARE start_time BIGINT;
    DECLARE end_time BIGINT;
    DECLARE i INT DEFAULT 0;
    
    -- 测试BLACKHOLE引擎性能
    DROP TABLE IF EXISTS test_blackhole;
    CREATE TABLE test_blackhole (
        id INT,
        data VARCHAR(255)
    ) ENGINE = BLACKHOLE;
    
    SET start_time = UNIX_TIMESTAMP(NOW(6));
    
    WHILE i < 10000 DO
        INSERT INTO test_blackhole VALUES (i, REPEAT('X', 200));
        SET i = i + 1;
    END WHILE;
    
    SET end_time = UNIX_TIMESTAMP(NOW(6));
    SELECT CONCAT('BLACKHOLE引擎耗时: ', (end_time - start_time), ' 秒') AS result;
    
    -- 测试InnoDB引擎性能
    SET i = 0;
    DROP TABLE IF EXISTS test_innodb;
    CREATE TABLE test_innodb (
        id INT,
        data VARCHAR(255)
    ) ENGINE = InnoDB;
    
    SET start_time = UNIX_TIMESTAMP(NOW(6));
    
    WHILE i < 10000 DO
        INSERT INTO test_innodb VALUES (i, REPEAT('X', 200));
        SET i = i + 1;
    END WHILE;
    
    SET end_time = UNIX_TIMESTAMP(NOW(6));
    SELECT CONCAT('InnoDB引擎耗时: ', (end_time - start_time), ' 秒') AS result;
END$$

DELIMITER ;

CALL performance_benchmark();

-- 使用BLACKHOLE引擎处理触发器逻辑
CREATE TABLE user_actions (
    id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT,
    action_type VARCHAR(50),
    action_time DATETIME DEFAULT CURRENT_TIMESTAMP
) ENGINE = InnoDB;

-- BLACKHOLE表用于触发器处理
CREATE TABLE action_statistics (
    user_id INT,
    action_count INT,
    last_action_time DATETIME
) ENGINE = BLACKHOLE;

DELIMITER $$

CREATE TRIGGER after_user_action
AFTER INSERT ON user_actions
FOR EACH ROW
BEGIN
    -- 复杂的业务逻辑处理
    DECLARE current_count INT DEFAULT 0;
    
    -- 统计用户操作次数（实际不存储）
    INSERT INTO action_statistics 
    VALUES (NEW.user_id, 1, NEW.action_time)
    ON DUPLICATE KEY UPDATE 
        action_count = action_count + 1,
        last_action_time = NEW.action_time;
        
    -- 其他业务逻辑...
    IF NEW.action_type = 'login' THEN
        -- 记录登录特殊处理
        INSERT INTO action_statistics VALUES (NEW.user_id, -1, NEW.action_time);
    END IF;
END$$

DELIMITER ;

-- 单表引擎转换
ALTER TABLE audit_logs ENGINE = InnoDB;

-- 批量转换脚本
SET @database_name = 'your_database';

SELECT 
    CONCAT('ALTER TABLE `', TABLE_NAME, '` ENGINE = InnoDB;') AS alter_statement,
    TABLE_NAME,
    TABLE_ROWS
FROM information_schema.TABLES 
WHERE TABLE_SCHEMA = @database_name 
AND ENGINE = 'BLACKHOLE'
ORDER BY TABLE_NAME;

-- 执行生成的ALTER语句
-- ALTER TABLE `audit_logs` ENGINE = InnoDB;
-- ALTER TABLE `temporary_metrics` ENGINE = InnoDB;

-- 1. 检查表结构和依赖关系
SHOW CREATE TABLE problematic_table;

-- 2. 检查相关触发器
SHOW TRIGGERS WHERE `Table` = 'problematic_table';

-- 3. 创建备份表
CREATE TABLE problematic_table_backup LIKE problematic_table;
ALTER TABLE problematic_table_backup ENGINE = InnoDB;

-- 4. 迁移数据（如果BLACKHOLE表有特殊数据来源）
-- 注意：标准的BLACKHOLE表没有数据，但可能有其他数据源
INSERT INTO problematic_table_backup 
SELECT * FROM problematic_table;

-- 5. 重命名表完成切换
RENAME TABLE 
    problematic_table TO problematic_table_old,
    problematic_table_backup TO problematic_table;

-- 6. 验证后清理
-- DROP TABLE problematic_table_old;

-- 自动化迁移存储过程
DELIMITER $$

CREATE PROCEDURE migrate_blackhole_tables(IN db_name VARCHAR(64))
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE table_name VARCHAR(64);
    DECLARE cur CURSOR FOR 
        SELECT TABLE_NAME 
        FROM information_schema.TABLES 
        WHERE TABLE_SCHEMA = db_name 
        AND ENGINE = 'BLACKHOLE';
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        GET DIAGNOSTICS CONDITION 1 @sqlstate = RETURNED_SQLSTATE;
        SELECT CONCAT('迁移失败: ', @sqlstate) AS error;
        ROLLBACK;
    END;
    
    START TRANSACTION;
    
    OPEN cur;
    
    read_loop: LOOP
        FETCH cur INTO table_name;
        IF done THEN
            LEAVE read_loop;
        END IF;
        
        -- 执行引擎转换
        SET @sql = CONCAT('ALTER TABLE `', db_name, '`.`', table_name, '` ENGINE = InnoDB');
        PREPARE stmt FROM @sql;
        EXECUTE stmt;
        DEALLOCATE PREPARE stmt;
        
        SELECT CONCAT('已转换: ', table_name) AS progress;
    END LOOP;
    
    CLOSE cur;
    COMMIT;
    
    SELECT '所有BLACKHOLE表转换完成' AS result;
END$$

DELIMITER ;

-- 执行批量迁移
CALL migrate_blackhole_tables('your_production_db');

-- 1. 识别所有BLACKHOLE表
SELECT 
    TABLE_SCHEMA,
    TABLE_NAME,
    TABLE_ROWS,
    CREATE_TIME
FROM information_schema.TABLES 
WHERE ENGINE = 'BLACKHOLE'
ORDER BY TABLE_SCHEMA, TABLE_NAME;

-- 2. 检查表依赖关系
SELECT 
    TABLE_NAME,
    TRIGGER_NAME,
    ACTION_TIMING,
    EVENT_MANIPULATION
FROM information_schema.TRIGGERS 
WHERE EVENT_OBJECT_SCHEMA = 'your_database';

-- 3. 验证外键约束
SELECT
    TABLE_NAME,
    COLUMN_NAME,
    CONSTRAINT_NAME,
    REFERENCED_TABLE_NAME,
    REFERENCED_COLUMN_NAME
FROM information_schema.KEY_COLUMN_USAGE
WHERE TABLE_SCHEMA = 'your_database'
AND REFERENCED_TABLE_NAME IS NOT NULL;

-- 1. 确认引擎转换成功
SELECT 
    TABLE_NAME,
    ENGINE,
    TABLE_ROWS
FROM information_schema.TABLES 
WHERE TABLE_SCHEMA = 'your_database'
AND TABLE_NAME IN ('previously_blackhole_table1', 'previously_blackhole_table2');

-- 2. 功能测试
-- 插入测试数据
INSERT INTO converted_table (test_column) VALUES ('功能测试数据');

-- 验证数据持久化
SELECT * FROM converted_table WHERE test_column = '功能测试数据';

-- 3. 性能基准测试
-- 比较转换前后的性能表现

-- 设置默认存储引擎为InnoDB
SET GLOBAL default_storage_engine = InnoDB;

-- 在my.cnf中永久配置
/*
[mysqld]
default-storage-engine = InnoDB
*/

-- 创建用户时限制引擎使用
CREATE USER 'app_user'@'%' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON your_database.* TO 'app_user'@'%';
REVOKE CREATE TEMPORARY TABLES, CREATE ROUTINE, ALTER ROUTINE 
ON *.* FROM 'app_user'@'%';

-- 代码审查中检查存储引擎使用
SELECT 
    ROUTINE_NAME,
    ROUTINE_DEFINITION
FROM information_schema.ROUTINES
WHERE ROUTINE_DEFINITION LIKE '%ENGINE=BLACKHOLE%'
   OR ROUTINE_DEFINITION LIKE '%BLACKHOLE%';

-- 监控新创建的BLACKHOLE表
SELECT 
    TABLE_SCHEMA,
    TABLE_NAME,
    CREATE_TIME
FROM information_schema.TABLES 
WHERE ENGINE = 'BLACKHOLE'
AND CREATE_TIME > DATE_SUB(NOW(), INTERVAL 1 DAY);

-- 方案1: 使用分区表模拟BLACKHOLE行为
CREATE TABLE audit_logs (
    id INT AUTO_INCREMENT,
    log_data JSON,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    partition_flag ENUM('keep', 'discard') DEFAULT 'discard'
) ENGINE = InnoDB
PARTITION BY LIST COLUMNS(partition_flag) (
    PARTITION p_keep VALUES IN ('keep'),
    PARTITION p_discard VALUES IN ('discard')
);

-- 定期清理"丢弃"分区的数据
ALTER TABLE audit_logs TRUNCATE PARTITION p_discard;

-- 方案2: 使用内存表+定期清理
CREATE TABLE temporary_data (
    id INT AUTO_INCREMENT PRIMARY KEY,
    session_data TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
) ENGINE = MEMORY;

-- 定期清理脚本
CREATE EVENT cleanup_temporary_data
ON SCHEDULE EVERY 1 HOUR
DO
    DELETE FROM temporary_data WHERE created_at < DATE_SUB(NOW(), INTERVAL 1 HOUR);