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);