Mariadb 数据库进阶学习一 表的重新认识

         通过简单的Sql语句创建表后，表是怎么存储的，以什么的方式进行存储的，占的磁盘空间是怎么算的？就是想通过深入学习，了解其内部构造结构。

MariaDB [db_test]> create table t8 (id int,sex char(1),username varchar(100),age tinyint,brithday date);
Query OK, 0 rows affected (0.028 sec)

        在磁盘中找到对应的数据表文件：

[root@172 /]# cd /var/lib/mysql/db_test
[root@172 db_test]# ls
db.opt  t2.frm  t2.ibd  t3.frm  t3.ibd  t5.frm  t5.ibd  t6.frm  t6.ibd  t7.frm  t7.ibd  t8.frm  t8.ibd

     两份文件对应的大小分别是：t8.frm 633B,t8.ibd 96KB (98.304B) ，借助hexdump命令查看此两文件

hexdump 参数
-C 每一字节以16进制显示，一行共16个字节，显示十六进制存储的文本内容
-b 每一字节以八进制显示，一行共16个字节，一行开始以十六进制显示偏移值；
  0000000 177 105 114 106 002 001 001 000 000 000 000 000 000 000 000 000
-c 每一字节以ASCII字符显示，其余同上；
  0000000 177 E L F 002 001 001 \0 \0 \0 \0 \0 \0 \0 \0 \0
-n 只解释指定长度字节
  单位：默认十进制，0x或0X开头则为16进制，0开头则为8进制。默认为字节，b则为512字节，k则为1024字节，m则为1048576字节
-d 双字节十进制显示
-o 双字节八进制显示
-v 去除中间显示的“*”字符
-x 双字节十六进制显示
-e 格式化参数

       具体查看：

[root@172 db_test]# hexdump -C  t8.frm
00000000  fe 01 0a 0c 12 00 56 00  01 00 44 03 00 00 10 00  |......V...D.....|  fe 01 固定头部 0a 0c 12 版本号
00000010  3a 01 00 00 00 00 00 00  00 00 00 02 08 00 09 00  |:...............|  IO_SIZE 
00000020  00 05 00 00 00 00 21 00  00 00 00 00 00 00 00 10  |......!.........|
00000030  00 00 00 3c 88 01 00 10  00 00 00 00 00 00 00 00  |...<............|
00000040  00 10 ad b8 52 30 3d b5  11 eb ac 4b 0c da 41 1d  |....R0=....K..A.|
00000050  8a 5a b0 01 00 00 00 00  00 00 02 00 ff 00 00 00  |.Z..............|
00000060  00 00 00 00 00 00 ff 00  00 00 00 20 20 20 00 00  |...........   ..|
00000070  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000001a0  00 00 06 00 49 6e 6e 6f  44 42 00 00 00 00 00 00  |....InnoDB......|      // 表存储的存储引擎
000001b0  94 01 94 01 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000002b0  00 00 05 00 00 00 48 01  00 00 3a 01 1f 00 00 00  |......H...:.....|   // 字段属性
000002c0  00 00 00 00 00 00 50 00  16 00 05 00 00 00 00 00  |......P.........|
000002d0  00 00 00 0b 00 02 00 00  1b 80 00 00 00 03 21 00  |..............!.|    03---int
000002e0  00 00 00 00 03 00 06 00  00 00 80 00 00 00 fe 21  |...............!|    fe---char
000002f0  00 00 00 00 00 2c 01 09  00 00 00 80 00 00 00 0f  |.....,..........|    of---varchar
00000300  21 00 00 00 00 00 04 00  37 01 00 0b 80 00 00 00  |!.......7.......|
00000310  01 21 00 00 00 00 00 0a  00 38 01 00 70 80 00 00  |.!.......8..p...|
00000320  00 0e 21 00 00 ff 69 64  ff 73 65 78 ff 75 73 65  |..!...id.sex.use|     // 表的字段
00000330  72 6e 61 6d 65 ff 61 67  65 ff 62 72 69 74 68 64  |rname.age.brithd|
00000340  61 79 ff 00                                       |ay..|
00000344

   字符集对应的16进制码： 21=utf8 08=latin1  1c=GBK

   这篇文章有更详细的解释：https://dev.mysql.com/doc/internals/en/frm-file-format.html