MySQL中的区
无论何种情况，区的大小总是1M，但是刚建表表分配的比较少。
1.创建一个数据库
mysql> create database vastdata;
Query OK, 1 row affected (0.01 sec)
2.使用这个数据库
mysql> use vastdata
Database changed
3.创建一张表
mysql> create table t1 (col1 int not null auto_increment,col2 varchar(7000),primary key(col1))engine=InnoDB;
Query OK, 0 rows affected (0.01 sec)
4.插入两条数据 其中repeat('a',7000)为将a连续7000次，也就是7000个a。所以我们将一条记录视为7K大小。
在MySQL中一个数据页的大小是16KB，所以两条记录就会占用一个页
mysql> insert t1 select null,repeat('a',7000);
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> insert t1 select null,repeat('a',7000);
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
5.查看t1表所对应的数据文件大小
mysql> system ls -lh /data/mydb/vastdata/t1.ibd
-rw-rw---- 1 mysql mysql 96K Oct 17 01:09 /data/mydb/vastdata/t1.ibd
6.使用py_innodb_page_info.py工具查看数据文件中页的分布
[root@vast python]# python py_innodb_page_info.py -v /data/mydb/vastdata/t1.ibd
page offset 00000000, page type #系统的页
page offset 00000001, page type #系统的页
page offset 00000002, page type #系统的页
page offset 00000003, page type , page level <0000> #存放数据的页
page offset 00000000, page type #空闲页
page offset 00000000, page type #空闲页
Total number of page: 6: #分配的页数
Freshly Allocated Page: 2 #空闲的页数
Insert Buffer Bitmap: 1 #系统中Insert Buffer Bitmap对应的页数
File Space Header: 1 #系统中File Space Header对应的页数
B-tree Node: 1 #存放数据的页数
File Segment inode: 1 系统中File Segment inode对应的页数
7.查看当前t1对应的数据文件大小
-rw-rw---- 1 mysql mysql 96K Oct 17 01:09 /data/mydb/vastdata/t1.ibd
这里会发现，t1表大小只有96K，没有直接分配1M。
8.再次插入一行记录，大小约为7KB
mysql> insert t1 select null,repeat('a',7000);
Query OK, 1 row affected (0.01 sec)
Records: 1 Duplicates: 0 Warnings: 0
9.再次查看数据文件大小，依然为96K
mysql> system ls -lh /data/mydb/vastdata/t1.ibd
-rw-rw---- 1 mysql mysql 96K Oct 17 01:15 /data/mydb/vastdata/t1.ibd
10.查看一下当前此数据文件的内部页分布
[root@vast python]# python py_innodb_page_info.py -v /data/mydb/vastdata/t1.ibd
page offset 00000000, page type
page offset 00000001, page type
page offset 00000002, page type
page offset 00000003, page type , page level <0001>
page offset 00000004, page type , page level <0000>
page offset 00000005, page type , page level <0000>
Total number of page: 6:
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 3
File Segment inode: 1
我们可以的看到，空闲页没有了。其中00000004,00000005为存放数据块 00000003为根所对应的块。
11.创建一个存储过程，目的是简化插入。
mysql> delimiter //
mysql> create procedure load_t1(count INT UNSIGNED)
-> begin
-> declare s int unsigned default 1;
-> declare c varchar(7000) default repeat('a',7000);
-> while s <= count DO
-> insert into t1 select NULL,c;
-> set s = s+1;
-> end while;
-> end;
-> //
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
12.执行这个存储过程，60则表示在表中插入60行，每行都是7000个a
mysql> call load_t1(60);
Query OK, 1 row affected (0.06 sec)
13.查看表有多少行记录，可见为63行
mysql> select count(*) from t1;
+----------+
| count(*) |
+----------+
| 63 |
+----------+
1 row in set (0.00 sec)
14.查看数据文件大小
mysql> system ls -lh /data/mydb/vastdata/t1.ibd
-rw-rw---- 1 mysql mysql 576K Oct 17 01:39 /data/mydb/vastdata/t1.ibd
63 * 7KB = 441KB 两行记录需要一个数据页，故这63行需要32个数据页
15.查看数据文件中页的分布，验证一下猜想
[root@vast python]# python py_innodb_page_info.py -v /data/mydb/vastdata/t1.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 00000006, page type <B-tree Node>, page level <0000>
page offset 00000007, page type <B-tree Node>, page level <0000>
page offset 00000008, page type <B-tree Node>, page level <0000>
page offset 00000009, page type <B-tree Node>, page level <0000>
page offset 0000000a, page type <B-tree Node>, page level <0000>
page offset 0000000b, page type <B-tree Node>, page level <0000>
page offset 0000000c, page type <B-tree Node>, page level <0000>
page offset 0000000d, page type <B-tree Node>, page level <0000>
page offset 0000000e, page type <B-tree Node>, page level <0000>
page offset 0000000f, page type <B-tree Node>, page level <0000>
page offset 00000010, page type <B-tree Node>, page level <0000>
page offset 00000011, page type <B-tree Node>, page level <0000>
page offset 00000012, page type <B-tree Node>, page level <0000>
page offset 00000013, page type <B-tree Node>, page level <0000>
page offset 00000014, page type <B-tree Node>, page level <0000>
page offset 00000015, page type <B-tree Node>, page level <0000>
page offset 00000016, page type <B-tree Node>, page level <0000>
page offset 00000017, page type <B-tree Node>, page level <0000>
page offset 00000018, page type <B-tree Node>, page level <0000>
page offset 00000019, page type <B-tree Node>, page level <0000>
page offset 0000001a, page type <B-tree Node>, page level <0000>
page offset 0000001b, page type <B-tree Node>, page level <0000>
page offset 0000001c, page type <B-tree Node>, page level <0000>
page offset 0000001d, page type <B-tree Node>, page level <0000>
page offset 0000001e, page type <B-tree Node>, page level <0000>
page offset 0000001f, page type <B-tree Node>, page level <0000>
page offset 00000020, page type <B-tree Node>, page level <0000>
page offset 00000021, 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>
Total number of page: 36:
Insert Buffer Bitmap: 1
File Space Header: 1
B-tree Node: 33
File Segment inode: 1
这里看到存放数据的数据页为33个，其中一个为根。32+1=33
16.在插入一行记录
mysql> call load_t1(1);
Query OK, 1 row affected (0.01 sec)
17.查看数据文件大小，发现这时，数据文件为2M
mysql> system ls -lh /data/mydb/vastdata/t1.ibd
-rw-rw---- 1 mysql mysql 2.0M Oct 17 01:50 /data/mydb/vastdata/t1.ibd
mysql>
18.查看数据文件中页的分布。
[root@vast python]# python py_innodb_page_info.py /data/mydb/vastdata/t1.ibd
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
可见这时，剩余91个空闲页。
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