一 前言
在讨论数据表字段设计的时候，有同学提出使用vabinary 代替 varchar ,部分开发不明所以,其实我也是。两者之间具体有什么区别？使用vabinary 代替 varchar 对业务有何优势？
二 对比测试
2.1 测试环境
数据库版本 Percona Server 5.6.24-72.2-log

create table vbinary

(

id int primary key auto_increment ,

val varbinary(776) not null default ''

) engine=innodb default charset=utf8mb4;

create table vachar

(

id int primary key auto_increment ,

val varchar(12) not null default ''

) engine=innodb default charset=utf8mb4;

insert into vbinary(val) values('abaa'),('aabb'),('bcdd'),('ccdd');

insert into vachar(val) values('abaa'),('aabb'),('bcdd'),('ccdd')

2.2 定义
varchar(N)字符串类型，用于存储变长字符串，使用表默认或者指定的校验集合，其中N代表存储字符的个数，详细信息请移步《浅谈varchar(N)》.
varbinary(N)二进制字符串类型，以二进制字节串存储字符,无字符集校验区别，均以二进制实际数值作比较。
2.3 长度定义
varchar存储的是字符个数，varbinary存储的是字节个数。

test [RW] 10:57:50 >insert into vbinary (val,name) value('2msdmlsdyo2enwlenw','disodmalsdsi');

Query OK, 1 row affected, 1 warning (0.00 sec)

test [RW] 10:57:55 >show warnings;

+---------+------+------------------------------------------+

| Level | Code | Message |

+---------+------+------------------------------------------+

| Warning | 1265 | Data truncated for column 'val' at row 1 |

+---------+------+------------------------------------------+

1 row in set (0.00 sec)

test [RW] 10:58:11 >insert into vbinary (val,name) value('有赞是一家移动零售服务提供商','disodmalsdsi');

Query OK, 1 row affected, 1 warning (0.01 sec)

test [RW] 10:59:00 >show warnings;

+---------+------+------------------------------------------+

| Level | Code | Message |

+---------+------+------------------------------------------+

| Warning | 1265 | Data truncated for column 'val' at row 1 |

+---------+------+------------------------------------------+

1 row in set (0.00 sec)

test [RW] 10:59:08 >select * from vbinary;

+----+--------------+--------------+

| id | val | name |

+----+--------------+--------------+

| 6 | 2msdmlsdyo2e | disodmalsdsi |

| 7 | 有赞是一 | disodmalsdsi | #

+----+--------------+--------------+

7 rows in set (0.00 sec)

test [RW] 10:59:12 >insert into vachar(val,name) value('有赞是一家移动零售服务提供商','disodmalsdsi');

Query OK, 1 row affected, 1 warning (0.00 sec)

test [RW] 11:00:02 >show warnings;

+---------+------+------------------------------------------+

| Level | Code | Message |

+---------+------+------------------------------------------+

| Warning | 1265 | Data truncated for column 'val' at row 1 |

+---------+------+------------------------------------------+

1 row in set (0.00 sec)

test [RW] 11:00:06 >select * from vachar;

+----+--------------------------------------+--------------+

| id | val | name |

+----+--------------------------------------+--------------+

| 4 | ccdd | yz |

| 5 | 有赞是一家移动零售服务提 | disodmalsdsi |

+----+--------------------------------------+--------------+

5 rows in set (0.00 sec)

分析:
varbinary(N)中长度N指的是字节串的长度,一个数字/英文字母占用1个字节，一个汉字占用3个字节(默认utf8、utf8mb4字符集),指定N 则可以存储 N 个数字或者字母,N/3个汉字。
varchar(N)中长度N指的是字符串的长度,一个数字/英文字母/汉字占用一个字符，指定N 可以存储N个字符。
注意两种存储类型支持的字段长度计算方式的不同，会给开发带来一定的困扰，使用varbinary的开发需要深入了解该字段的存储单位，设计字段的时候还要根据业务逻辑计算好N的值是多少。否则可能会被截断 ，在sql_mode为严格模式时则会报错。
2.4 索引功能
分别对name字段创建索引

test [RW] 10:47:01 >alter table vbinary add name varbinary(255) not null default 'yz';

Query OK, 0 rows affected (0.02 sec)

Records: 0 Duplicates: 0 Warnings: 0

test [RW] 10:47:24 >alter table vbinary add key idx_name(name);

Query OK, 0 rows affected (0.01 sec)

Records: 0 Duplicates: 0 Warnings: 0

test [RW] 10:48:25 >rename table vchar to vachar;

Query OK, 0 rows affected (0.01 sec)

test [RW] 10:49:00 >alter table vachar add name varchar(255) not null default 'yz';

Query OK, 0 rows affected (0.02 sec)

Records: 0 Duplicates: 0 Warnings: 0

test [RW] 10:49:31 >alter table vachar add key idx_name(name);

Query OK, 0 rows affected, 1 warning (0.02 sec)

Records: 0 Duplicates: 0 Warnings: 1

test [RW] 10:49:53 >show Warnings;

+---------+------+---------------------------------------------------------+

| Level | Code | Message |

+---------+------+---------------------------------------------------------+

| Warning | 1071 | Specified key was too long; max key length is 767 bytes |

+---------+------+---------------------------------------------------------+

1 row in set (0.00 sec)

test [RW] 10:50:06 >show create table vachar\G

*************************** 1. row ***************************

Table: vachar

Create Table: CREATE TABLE `vachar` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`val` varchar(12) NOT NULL DEFAULT '',

`name` varchar(255) NOT NULL DEFAULT 'yz',

PRIMARY KEY (`id`),

KEY `idx_name` (`name`(191))

) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4

1 row in set (0.00 sec)

test [RW] 10:50:19 >show create table vbinary \G

*************************** 1. row ***************************

Table: vbinary

Create Table: CREATE TABLE `vbinary` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`val` varbinary(12) NOT NULL DEFAULT '',

`name` varbinary(255) NOT NULL DEFAULT 'yz',

PRIMARY KEY (`id`),

KEY `idx_name` (`name`)

) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8mb4

1 row in set (0.00 sec)

test [RW] 11:53:08 >create table vbinary1

-> (

-> id int primary key auto_increment ,

-> val varbinary(776) not null default ''

-> ) engine=innodb default charset=utf8mb4;

Query OK, 0 rows affected (0.01 sec)

test [RW] 11:53:09 >alter table vbinary1 add key idx_val(val);

Query OK, 0 rows affected, 1 warning (0.02 sec)

Records: 0 Duplicates: 0 Warnings: 1

test [RW] 11:53:37 >show Warnings;

+---------+------+---------------------------------------------------------+

| Level | Code | Message |

+---------+------+---------------------------------------------------------+

| Warning | 1071 | Specified key was too long; max key length is 767 bytes |

+---------+------+---------------------------------------------------------+

1 row in set (0.00 sec)

test [RW] 11:53:44 >show create table vbinary1 \G

*************************** 1. row ***************************

Table: vbinary1

Create Table: CREATE TABLE `vbinary1` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`val` varbinary(776) NOT NULL DEFAULT '',

PRIMARY KEY (`id`),

KEY `idx_val` (`val`(767)) ## 被修改为 767 ，索引支持的最大字节数。

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

1 row in set (0.00 sec)

分析:
基于 varbinary和 varchar 存储字符的长度定义不同，varchar 可以存储字符串前191个字符的索引，varbinary 字段的索引则最多可以存储767字节。如果是英文字母则可以存储更长的字符串。
2.5 校验方面

test [RW] 12:15:06 >select * from vachar where val='ABAA';

+----+------+------+

| id | val | name |

+----+------+------+

| 1 | abaa | yz |

+----+------+------+

1 row in set (0.00 sec)

test [RW] 12:14:31 >select * from vbinary where val='ABAA';

Empty set (0.00 sec)

test [RW] 12:15:11 >select * from vbinary where val='abaa';

+----+------+------+

| id | val | name |

+----+------+------+

| 1 | abaa | yz |

+----+------+------+

1 row in set (0.00 sec)

分析:
varbinary存储的是二进制字节串而不是字符串，这意味着它没有字符集校验的概念，排序和比较都是基于字节中的实际数值大小进行的。varchar类型存储的列在比较的时候是通过字符集的方式进行的,varchar 中'ABAA'和'abaa'是一致的.
2.6 性能测试
使用mysqlslap 进行10个并发100w次查询做对比

[root@rac4 00:31:35 ~]

# time mysqlslap --no-defaults -uroot --create-schema=test -S /srv/my3306/run/mysql.sock --number-of-queries=1000000 --concurrency=10 --query="select * from vbinary where val='abaa';"

Benchmark

Average number of seconds to run all queries: 30.569 seconds

Minimum number of seconds to run all queries: 30.569 seconds

Maximum number of seconds to run all queries: 30.569 seconds

Number of clients running queries: 10

Average number of queries per client: 100000

real 0m30.574s

user 0m8.124s

sys 0m6.286s

[root@rac4 00:32:18 ~]

# time mysqlslap --no-defaults -uroot --create-schema=test -S /srv/my3306/run/mysql.sock --number-of-queries=1000000 --concurrency=10 --query="select * from vachar where val='abaa';"

Benchmark

Average number of seconds to run all queries: 31.986 seconds

Minimum number of seconds to run all queries: 31.986 seconds

Maximum number of seconds to run all queries: 31.986 seconds

Number of clients running queries: 10

Average number of queries per client: 100000

real 0m31.991s

user 0m8.351s

sys0m6.407s

分析
简单的select查询对比来看
varbinary 30.569s
varchar31.986s
varbinary 相对性能有 1.4s 约4%的性能提升，在压测环境下每秒几乎3wqps，如果是普通的业务场景1000-2000左右的qps，varbinary带来的性能可以忽略不计.