mysql删除操作其实是假删除问题

CREATE TABLE `t` (
  `id` int(11) NOT NULL,
  `a` int(11) DEFAULT NULL,
  `b` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `a` (`a`),
  KEY `b` (`b`)
) ENGINE=InnoDB;

#定义分割符号，mysql 默认分割符为分号;，这里定义为 //
#分隔符的作用主要是告诉mysql遇到下一个 // 符号即执行上面这一整段sql语句
delimiter //
 
#创建一个存储过程，并命名为 testData
create procedure testData() 
 
#下面这段就是表示循环往表里插入10w条数据
begin
  declare i int;
  set i=1;
  while(i<=100000)do
    insert into t values(i, i, i);
    set i=i+1;
  end while;
end //  #这里遇到//符号，即执行上面一整段sql语句
 
delimiter ; #恢复mysql分隔符为;
 
call testData(); #调用存储过程

#下面这两条命令可以查看表文件所占空间大小
mysql> use infORMation_schema;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'M') from tables where table_schema='test' AND table_name='t';
+-------------------------------------------------+
| concat(round(sum(DATA_LENGTH/1024/1024),2),'M') |
+-------------------------------------------------+
| 3.52M                                           |
+-------------------------------------------------+
1 row in set (0.04 sec)

#先删除表所有数据，再重新查看表文件大小
mysql> delete from t;
Query OK, 100000 rows affected (0.46 sec)
 
mysql> use information_schema;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'M') from tables where table_schema='test' AND table_name='t';
+-------------------------------------------------+
| concat(round(sum(DATA_LENGTH/1024/1024),2),'M') |
+-------------------------------------------------+
| 3.52M                                           |
+-------------------------------------------------+
1 row in set (0.00 sec)

optimizetablet

mysql> optimize table t;
+--------+----------+----------+-------------------------------------------------------------------+
| Table  | Op       | Msg_type | Msg_text                                                          |
+--------+----------+----------+-------------------------------------------------------------------+
| test.t | optimize | note     | Table does not support optimize, doing recreate + analyze instead |
| test.t | optimize | status   | OK                                                                |
+--------+----------+----------+-------------------------------------------------------------------+
2 rows in set (0.39 sec)
 
mysql> use information_schema;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> select concat(round(sum(DATA_LENGTH/1024/1024),2),'M') from tables where table_schema='test' AND table_name='t';
+-------------------------------------------------+
| concat(round(sum(DATA_LENGTH/1024/1024),2),'M') |
+-------------------------------------------------+
| 0.02M                                           |
+-------------------------------------------------+
1 row in set (0.00 sec)

altertabletengine=InnoDB