InnoDB -- 逻辑存储

本文主要介绍InnoDB存储引擎的逻辑存储结构

逻辑存储结构

Tablespace

  1. Tablespace是InnoDB存储引擎逻辑存储结构的最高层所有数据都存放在Tablespace中
  2. 分类
    • System Tablespace
    • Separate Tablespace
    • General Tablespace

System Tablespace

  1. System Tablespace即我们常见的共享表空间,变量为innodb_data_file_path,一般为ibdata1文件
  2. 里面存放着undo logschange bufferdoublewrite buffer等信息(后续将详细介绍),在没有开启file-per-table的情况下,还会包含所有表的索引和数据信息
  3. 没有开启file-per-table时存在的问题
    • 所有的表和索引都会在System Tablespace中,占用空间会越来越大
    • 碎片越来越多(如truncate table时,占用的磁盘空间依旧保留在System Tablespace
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mysql>  SHOW VARIABLES LIKE 'innodb_data_file_path';
+-----------------------+------------------------+
| Variable_name | Value |
+-----------------------+------------------------+
| innodb_data_file_path | ibdata1:12M:autoextend |
+-----------------------+------------------------+
1 row in set (0.01 sec)

mysql> SHOW VARIABLES LIKE '%datadir%';
+---------------+-----------------+
| Variable_name | Value |
+---------------+-----------------+
| datadir | /var/lib/mysql/ |
+---------------+-----------------+
1 row in set (0.01 sec)

mysql> system sudo ls -lh /var/lib/mysql/ibdata1
[sudo] password for zhongmingmao:
-rw-r----- 1 mysql mysql 76M May 6 20:00 /var/lib/mysql/ibdata1

Separate Tablespace

  1. MySQL参考手册中并没有Separate Tablespace这个术语,这里只为了行文方便,表示在开启file-per-table的情况下,每个表有自己独立的表空间,变量为innodb_file_per_table
  2. 里面存放在每个表的索引和数据信息,后缀一般为.ibd
  3. 默认初始大小为96KB
  4. 好处
    • 避免System Tablespace越来越大
    • 减少碎片(truncate table,操作系统会自动回收空间
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mysql> use test
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> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t |
+----------------+
1 row in set (0.00 sec)

mysql> SHOW VARIABLES LIKE 'innodb_file_per_table';
+-----------------------+-------+
| Variable_name | Value |
+-----------------------+-------+
| innodb_file_per_table | ON |
+-----------------------+-------+
1 row in set (0.00 sec)

mysql> SHOW VARIABLES LIKE '%datadir%'; +---------------+-----------------+
| Variable_name | Value |
+---------------+-----------------+
| datadir | /var/lib/mysql/ |
+---------------+-----------------+
1 row in set (0.01 sec)

mysql> system sudo ls -lh /var/lib/mysql/test
total 112K
-rw-r----- 1 mysql mysql 61 Apr 28 10:18 db.opt
-rw-r----- 1 mysql mysql 8.4K May 7 17:03 t.frm
-rw-r----- 1 mysql mysql 96K May 7 17:03 t.ibd

General Tablespace

  1. General TablespaceMySQL 5.7.6引入的新特性,具体内容请参照下面链接
    15.7.9 InnoDB General Tablespaces

Segment

  1. Segment分为三种
    1. Leaf node segment数据段,B+Tree的叶子节点
    2. Non-Leaf node segment索引段,B+Tree的非叶子节点
    3. Rollback segment:回滚段,存放undo log,默认是位于System Tablespace
  2. InnoDB中的B+Tree索引,由Leaf node segmentNon-Leaf node segment组成
  3. 一个Segment由多个Extent和Page组成

Extent

  1. Extent是由连续页(默认页大小为16KB)组成,在默认页大小时,为64个连续页,大小为64*16KB=1MB
    • 不同页大小:4KB*256 or 8KB*128 or 16KB*64 or 32KB*64 or 64KB*64
  2. 为了保证页的连续性,InnoDB可以一次性从磁盘申请4个Extent
  3. 为了节省磁盘空间,如表的数据量很小(Leaf node segmentNon-Leaf node segment都很小)或Rollback segment,Segment一开始不会直接申请Extent,而是先用32个碎片页(用于叶子节点)来存放数据,用完之后才继续对Extent(1MB)的申请(下面实例是Leaf Node Segment的对空间的申请过程)

下列操作过程中涉及到了ROW_FORMAT的部分内容,本文并没有详细展开,只为佐证结果

创建表

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# 创建表
mysql> CREATE TABLE t (
-> a INT NOT NULL AUTO_INCREMENT,
-> b VARCHAR(7000),
-> PRIMARY KEY (a)
-> ) ENGINE=INNODB ROW_FORMAT=COMPACT CHARSET=LATIN1;
Query OK, 0 rows affected (0.03 sec)

mysql> system sudo ls -lh /var/lib/mysql/test/t.ibd
-rw-r----- 1 mysql mysql 96K May 7 17:09 /var/lib/mysql/test/t.ibd
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# 查看表空间信息
$ sudo python py_innodb_page_info.py -v /var/lib/mysql/test/t.ibd
page offset 00000000, page type <File Space Header>
page offset 00000001, page type <Insert Buffer Bitmap>
page offset 00000002, page type <File Segment inode>
page offset 00000003, page type <B-tree Node>, page level <0000>
page offset 00000000, page type <Freshly Allocated Page>
page offset 00000000, page type <Freshly Allocated Page>
Total number of page: 6:
Freshly Allocated Page: 2
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 1
File Segment inode: 1
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# 查看表空间文件十六进制(Vim,:%!xxd)
# page offset=3
0000c000: 18f8 857f 0000 0003 ffff ffff ffff ffff ................
0000c010: 0000 0000 4087 2c32 45bf 0000 0000 0000 ....@.,2E.......
0000c020: 0000 0000 0111 0002 0078 8002 0000 0000 .........x......
0000c030: 0000 0005 0000 0000 0000 0000 0000 0000 ................
0000c040: 0000 0000 0000 0000 0155 0000 0111 0000 .........U......
0000c050: 0002 00f2 0000 0111 0000 0002 0032 0100 .............2..
0000c060: 0200 0d69 6e66 696d 756d 0001 000b 0000 ...infimum......
0000c070: 7375 7072 656d 756d 0000 0000 0000 0000 supremum........
0000c080: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000c090: 0000 0000 0000 0000 0000 0000 0000 0000 ................
......
0000ffd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000ffe0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000fff0: 0000 0000 0070 0063 18f8 857f 4087 2c32 .....p.c....@.,2
  1. py_innodb_page_info.py是姜承尧大神用Python写的用来分析表空间中的各页类型和信息的工具
  2. b VARCHAR(7000)能保证一个页中最多存放两条记录,2 < 16KB/7000B < 3
  3. 单独表空间t.ibd的默认大小为96KB
  4. 单独表空间t.ibd目前只有一个B+Tree叶子节点page level <0000>),还有两个可用页Freshly Allocated Page
    • page offset=3(16K)*3 = 0xc000,该页范围为0xc000 ~ 0xffff
    • 理论上0xc078第一个记录的开始,此时尚未插入任何记录,所以为0(行记录格式ROW_FORMAT后续将详细介绍)

插入2条记录

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# 插入2条记录
mysql> INSERT INTO t SELECT NULL,REPEAT('a',7000);
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> INSERT INTO t SELECT NULL,REPEAT('a',7000);
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> system sudo ls -lh /var/lib/mysql/test/t.ibd
[sudo] password for zhongmingmao:
-rw-r----- 1 mysql mysql 96K May 7 17:26 /var/lib/mysql/test/t.ibd
mysql>
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# 查看表空间信息
$ sudo python py_innodb_page_info.py -v /var/lib/mysql/test/t.ibd
page offset 00000000, page type <File Space Header>
page offset 00000001, page type <Insert Buffer Bitmap>
page offset 00000002, page type <File Segment inode>
page offset 00000003, page type <B-tree Node>, page level <0000>
page offset 00000000, page type <Freshly Allocated Page>
page offset 00000000, page type <Freshly Allocated Page>
Total number of page: 6:
Freshly Allocated Page: 2
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 1
File Segment inode: 1
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# 查看表空间文件十六进制(Vim,:%!xxd)
# page offset=3
0000c000: f185 f4c0 0000 0003 ffff ffff ffff ffff ................
0000c010: 0000 0000 4087 697e 45bf 0000 0000 0000 ....@.i~E.......
0000c020: 0000 0000 0111 0002 375a 8004 0000 0000 ........7Z......
0000c030: 1bf1 0002 0001 0002 0000 0000 0000 0000 ................
0000c040: 0000 0000 0000 0000 0155 0000 0111 0000 .........U......
0000c050: 0002 00f2 0000 0111 0000 0002 0032 0100 .............2..
0000c060: 0200 1d69 6e66 696d 756d 0003 000b 0000 ...infimum......
0000c070: 7375 7072 656d 756d 589b 0000 0010 1b71 supremumX......q
0000c080: 8000 0001 0000 0014 0869 cc00 0002 1001 .........i......
0000c090: 1061 6161 6161 6161 6161 6161 6161 6161 .aaaaaaaaaaaaaaa
0000c0a0: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
......
0000dbd0: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
0000dbe0: 6161 6161 6161 6161 6158 9b00 0000 18e4 aaaaaaaaaX......
0000dbf0: 7f80 0000 0200 0000 1408 6acd 0000 01a4 ..........j.....
0000dc00: 0110 6161 6161 6161 6161 6161 6161 6161 ..aaaaaaaaaaaaaa
......
0000f730: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
0000f740: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
0000f750: 6161 6161 6161 6161 6161 0000 0000 0000 aaaaaaaaaa......
......
0000ffd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000ffe0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0000fff0: 0000 0000 0070 0063 f185 f4c0 4087 697e .....p.c....@.i~
......
  1. 表空间大小依旧是96KB,2条记录可以完全放入page offset=3的B+Tree叶子节点中
  2. 第1条记录位于page offset=3的页,地址范围为0xc078 ~ 0xdbe8,占用7025 Byte
  3. 第2条记录位于page offset=3的页,地址范围为0xdbe9 ~ 0xf759,占用7025 Byte
  4. 此时,page offset=3的页已经无法再容纳下一条同样长度的记录,但此时还有2个可用页,可用于B+Tree的分裂(此时只有叶子节点)

插入第3条记录

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# 插入第3条记录
mysql> INSERT INTO t SELECT NULL,REPEAT('a',7000);
Query OK, 1 row affected (0.03 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> system sudo ls -lh /var/lib/mysql/test/t.ibd
-rw-r----- 1 mysql mysql 96K May 7 17:40 /var/lib/mysql/test/t.ibd
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# 查看表空间信息
$ sudo python py_innodb_page_info.py -v /var/lib/mysql/test/t.ibd
page offset 00000000, page type <File Space Header>
page offset 00000001, page type <Insert Buffer Bitmap>
page offset 00000002, page type <File Segment inode>
page offset 00000003, page type <B-tree Node>, page level <0001>
page offset 00000004, page type <B-tree Node>, page level <0000>
page offset 00000005, page type <B-tree Node>, page level <0000>
Total number of page: 6:
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 3
File Segment inode: 1
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# 查看表空间文件十六进制(Vim,:%!xxd)
# page offset=4
00010000: 669d db54 0000 0004 ffff ffff 0000 0005 f..T............
00010010: 0000 0000 4087 e2e4 45bf 0000 0000 0000 ....@...E.......
00010020: 0000 0000 0111 0002 375a 8004 1bf1 1b71 ........7Z.....q
00010030: 0000 0005 0000 0001 0000 0000 0000 0000 ................
00010040: 0000 0000 0000 0000 0155 0000 0000 0000 .........U......
00010050: 0000 0000 0000 0000 0000 0000 0000 0100 ................
00010060: 0200 1d69 6e66 696d 756d 0002 000b 0000 ...infimum......
00010070: 7375 7072 656d 756d 589b 0000 0010 fff0 supremumX.......
00010080: 8000 0001 0000 0014 0869 cc00 0002 1001 .........i......
00010090: 1061 6161 6161 6161 6161 6161 6161 6161 .aaaaaaaaaaaaaaa
......
00011bd0: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
00011be0: 6161 6161 6161 6161 6158 9b00 0000 1800 aaaaaaaaaX......
00011bf0: 0080 0000 0200 0000 1408 6acd 0000 01a4 ..........j.....
00011c00: 0110 6161 6161 6161 6161 6161 6161 6161 ..aaaaaaaaaaaaaa
......
00013740: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
00013750: 6161 6161 6161 6161 6161 0000 0000 0000 aaaaaaaaaa......
00013760: 0000 0000 0000 0000 0000 0000 0000 0000 ................
......
00013fd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00013fe0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00013ff0: 0000 0000 0070 0063 669d db54 4087 e2e4 .....p.cf..T@...

# page offset=5
00014000: 946a 9d01 0000 0005 0000 0004 ffff ffff .j..............
00014010: 0000 0000 4087 e2e4 45bf 0000 0000 0000 ....@...E.......
00014020: 0000 0000 0111 0002 375a 8004 0000 0000 ........7Z......
00014030: 1bf1 0005 0000 0002 0000 0000 0000 0000 ................
00014040: 0000 0000 0000 0000 0155 0000 0000 0000 .........U......
00014050: 0000 0000 0000 0000 0000 0000 0000 0100 ................
00014060: 0200 1d69 6e66 696d 756d 0003 000b 0000 ...infimum......
00014070: 7375 7072 656d 756d 589b 0000 0010 1b71 supremumX......q
00014080: 8000 0002 0000 0014 086a cd00 0001 a401 .........j......
00014090: 1061 6161 6161 6161 6161 6161 6161 6161 .aaaaaaaaaaaaaaa
......
00015bd0: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
00015be0: 6161 6161 6161 6161 6158 9b00 0000 18e4 aaaaaaaaaX......
00015bf0: 7f80 0000 0300 0000 1408 6fd0 0000 0211 ..........o.....
00015c00: 0110 6161 6161 6161 6161 6161 6161 6161 ..aaaaaaaaaaaaaa
.......
00017740: 6161 6161 6161 6161 6161 6161 6161 6161 aaaaaaaaaaaaaaaa
00017750: 6161 6161 6161 6161 6161 0000 0000 0000 aaaaaaaaaa......
00017760: 0000 0000 0000 0000 0000 0000 0000 0000 ................
......
00017fd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00017fe0: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00017ff0: 0000 0000 0070 0063 946a 9d01 4087 e2e4 .....p.c.j..@...
  1. 插入第3条记录后,表空间大小依旧为96KB,因为插入之前还有两个可用页,有足够的空间让B+Tree分裂
  2. page offset=3page level<0001>,表示这是倒数第一层B+Tree索引节点
  3. 实际的记录存放在page offset45B+Tree叶子节点,即上一操作后的可用页
  4. 第1条记录位于page offset=4的页,地址范围为0x10078 ~ 0x11be8,占用7025 Byte
  5. 第2条记录位于page offset=4的页,地址范围为0x11be9 ~ 0x13759,占用7025 Byte
    • 第2条记录同时也位于page offset=5的页,地址范围为0x14078 ~ 0x15be8,占用7025 Byte
  6. 第3条记录位于page offset=5的页,地址范围为0x15be9 ~ 0x17759,占用7025 Byte
  7. 此时,page offset=4page offset=5的页都已经无法再容纳同样长度的记录,而且表空间初始的96KB已无可用页
    • 在插入同样长度的记录,表空间会增大

创建存储过程

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mysql> DELIMITER //
mysql> CREATE PROCEDURE load_t (count INT UNSIGNED)
-> BEGIN
-> DECLARE s INT UNSIGNED DEFAULT 1;
-> DECLARE c VARCHAR(7000) DEFAULT REPEAT('a',7000);
-> WHILE s <= count DO
-> INSERT INTO t SELECT NULL,c;
-> SET s=s+1;
-> END WHILE;
-> END;
-> //
Query OK, 0 rows affected (0.09 sec)

mysql> DELIMITER ;

插入60条记录

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# 通过调用存储过程,插入60条记录
mysql> CALL load_t(60);
Query OK, 1 row affected (0.67 sec)

mysql> system sudo ls -lh /var/lib/mysql/test/t.ibd
-rw-r----- 1 mysql mysql 592K May 8 01:58 /var/lib/mysql/test/t.ibd
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# 查看表空间信息
$ sudo python py_innodb_page_info.py -v /var/lib/mysql/test/t.ibd
page offset 00000000, page type <File Space Header>
page offset 00000001, page type <Insert Buffer Bitmap>
page offset 00000002, page type <File Segment inode>
page offset 00000003, page type <B-tree Node>, page level <0001>
page offset 00000004, page type <B-tree Node>, page level <0000>
page offset 00000005, page type <B-tree Node>, page level <0000>
......
page offset 00000022, page type <B-tree Node>, page level <0000>
page offset 00000023, page type <B-tree Node>, page level <0000>
page offset 00000000, page type <Freshly Allocated Page>
Total number of page: 37:
Freshly Allocated Page: 1
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 33
File Segment inode: 1
  1. 此时,表空间大小依旧小于Extent大小(1MB),目前还是通过碎片页来申请数据空间
  2. 上一步操作中,默认的表空间大小已无法再容纳新的同样长度的记录,且已使用了2个B+Tree叶子节点Leaf Node Segment在申请Extent前可以再使用30个B+Tree叶子节点,所以再插入60条记录(每页只能容纳2条记录)
  3. 此时处于临界状态B+Tree叶子节点为32个,再插入同样长度的记录时,Leaf Node Segment将进行Extent的申请

插入第64条记录

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# 插入第64条记录
mysql> CALL load_t(1);
Query OK, 1 row affected (0.05 sec)

mysql> system sudo ls -lh /var/lib/mysql/test/t.ibd
[sudo] password for zhongmingmao:
-rw-r----- 1 mysql mysql 2.0M May 8 02:14 /var/lib/mysql/test/t.ibd
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# 查看表空间信息
$ sudo python py_innodb_page_info.py -v /var/lib/mysql/test/t.ibd
page offset 00000000, page type <File Space Header>
page offset 00000001, page type <Insert Buffer Bitmap>
page offset 00000002, page type <File Segment inode>
page offset 00000003, page type <B-tree Node>, page level <0001>
page offset 00000004, page type <B-tree Node>, page level <0000>
page offset 00000005, page type <B-tree Node>, page level <0000>
......
page offset 00000022, page type <B-tree Node>, page level <0000>
page offset 00000023, page type <B-tree Node>, page level <0000>
page offset 00000000, page type <Freshly Allocated Page>
......
page offset 00000000, page type <Freshly Allocated Page>
page offset 00000040, page type <B-tree Node>, page level <0000>
page offset 00000000, page type <Freshly Allocated Page>
......
page offset 00000000, page type <Freshly Allocated Page>
page offset 00000000, page type <Freshly Allocated Page>
Total number of page: 128:
Freshly Allocated Page: 91
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 34
File Segment inode: 1
  1. 插入第64条记录时,Leaf Node Segment就需要进行Extent的申请,从page offset=0x40处申请一个Extent0x40*16KB=1MB),此时表空间大小为2MB

Page

  1. Page是InnoDB磁盘管理的最小单位,变量为innodb_page_size
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mysql>  SHOW VARIABLES LIKE 'innodb_page_size';
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| innodb_page_size | 16384 |
+------------------+-------+
1 row in set (0.17 sec)

Row

  1. InnoDB存储引擎的数据是按行进行存放的
  2. 行记录格式Row_FORMAT将在后续详细介绍

参考资料

  1. MySQL技术内幕 - InnoDB存储引擎 V2
  2. MySQL 5.7 Reference Manual
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