Mysql不像ORACLE，提供各种各样的dump方式 ，可以了解数据库的各种内存结构，数据存储结构。mysql只有少量的一些trace方式，下面向大家介绍如何通过innodb_table_monitor来窥视innodb存储引擎表及其索引的存储方式。这篇文章，也纠正上一篇文章《INNODB与ORACLE单行存储长度对比》中存在的问题，上文中将oracle中一个table的大小实际上与mysql(table+primary index)进行了比较，这个比较本身就是不公平的，对大家的误导表示歉意。
创建数据库
create database dc_test
character set gbk;
创建测试表test1
CREATE TABLE `test1` (
`id` int(11) NOT NULL auto_increment,
`title` varchar(50) NOT NULL,
`user_id` int(11) NOT NULL,
`gmt_create` datetime NOT NULL,
`gmt_modified` datetime NOT NULL,
PRIMARY KEY (`id`),
KEY `idx_test1_userid` (`user_id`,`gmt_create`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk
重复写入数据
mysql> insert into test1(title,user_id,gmt_create,gmt_modified) values(‘this is a test’,1001,now(),now());
Query OK, 1 row affected (0.00 sec)mysql> insert into test1(title,user_id,gmt_create,gmt_modified) select title,user_id,gmt_create,gmt_modified from test1;
Query OK, 786432 rows affected (13.65 sec)
Records: 786432 Duplicates: 0 Warnings: 0mysql> select count(*) from test1;
+———-+
| count(*) |
+———-+
| 1572864 |
+———-+
1 row in set (0.59 sec)
创建一张只有主键的测试表
CREATE TABLE `test2` (
`id` int(11) NOT NULL auto_increment,
`title` varchar(50) NOT NULL,
`user_id` int(11) NOT NULL,
`gmt_create` datetime NOT NULL,
`gmt_modified` datetime NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk
创建一张没有主键的测试表test3
CREATE TABLE `test3` (
`id` int(11) NOT NULL,
`title` varchar(50) NOT NULL,
`user_id` int(11) NOT NULL,
`gmt_create` datetime NOT NULL,
`gmt_modified` datetime NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=gbk
创建innodb_table_monitor表，通知innodb存储引擎将数据输出到/etc/my.cnf中定义的log-error文件里
mysql> create table innodb_table_monitor(a int) engine=innodb;
Query OK, 0 rows affected (0.05 sec)
===========================================
090623 8:15:25 INNODB TABLE MONITOR OUTPUT
===========================================
————————————–
TABLE: name dc_test/innodb_table_monitor, id 0 24, columns 5, indexes 1, appr.rows 0
COLUMNS: a: DATA_INT len 4 prec 0; DB_ROW_ID: DATA_SYS prtype 256 len 6 prec 0; DB_TRX_ID: DATA_SYS prtype 257 len 6 prec 0; DB_ROLL_PTR: DATA_SYS prtype 258 len 7 prec 0;
INDEX: name GEN_CLUST_INDEX, id 0 28, fields 0/4, type 1
root page 50, appr.key vals 0, leaf pages 1, size pages 1
FIELDS: DB_ROW_ID DB_TRX_ID DB_ROLL_PTR a
–
————————————–
TABLE: name dc_test/test1, id 0 22, columns 9, indexes 2, appr.rows 1573185
COLUMNS: id: DATA_INT len 4 prec 0; title: type 12 len 100 prec 0; user_id: DATA_INT len 4 prec 0; gmt_create: DATA_INT len 8 prec 0; gmt_modified: DATA_INT len 8 prec 0; DB_ROW_ID: DATA_SYS prtype 256 len 6 prec 0; DB_TRX_ID: DATA_SYS prtype 257 len 6 prec 0; DB_ROLL_PTR: DATA_SYS prtype 258 len 7 prec 0;
INDEX: name PRIMARY, id 0 25, fields 1/7, type 3
root page 57, appr.key vals 1573185, leaf pages 5959, size pages 5991 –注意这个值
FIELDS: id DB_TRX_ID DB_ROLL_PTR title user_id gmt_create gmt_modified
INDEX: name idx_test1_userid, id 0 26, fields 2/3, type 0
root page 62, appr.key vals 9, leaf pages 2093, size pages 2279
FIELDS: user_id gmt_create id
–主键与表的数据是存放在一起的,所以primary index(size pages 5991) 比 second index(size pages 2279) 大;从索引字段上看，second index(idx_test1_userid)包含primary indexed columns(id)
————————————–
TABLE: name dc_test/test2, id 0 14, columns 9, indexes 1, appr.rows 0
COLUMNS: id: DATA_INT len 4 prec 0; title: type 12 len 100 prec 0; user_id: DATA_INT len 4 prec 0; gmt_create: DATA_INT len 8 prec 0; gmt_modified: DATA_INT len 8 prec 0; DB_ROW_ID: DATA_SYS prtype 256 len 6 prec 0; DB_TRX_ID: DATA_SYS prtype 257 len 6 prec 0; DB_ROLL_PTR: DATA_SYS prtype 258 len 7 prec 0;
INDEX: name PRIMARY, id 0 16, fields 1/7, type 3
root page 63, appr.key vals 0, leaf pages 1, size pages 1
FIELDS: id DB_TRX_ID DB_ROLL_PTR title user_id gmt_create gmt_modified
–主键与表的数据是存放在一起的
————————————–
TABLE: name dc_test/test3, id 0 17, columns 9, indexes 1, appr.rows 0
COLUMNS: id: DATA_INT len 4 prec 0; title: type 12 len 100 prec 0; user_id: DATA_INT len 4 prec 0; gmt_create: DATA_INT len 8 prec 0; gmt_modified: DATA_INT len 8 prec 0; DB_ROW_ID: DATA_SYS prtype 256 len 6 prec 0; DB_TRX_ID: DATA_SYS prtype 257 len 6 prec 0; DB_ROLL_PTR: DATA_SYS prtype 258 len 7 prec 0;
INDEX: name GEN_CLUST_INDEX, id 0 19, fields 0/8, type 1
root page 213, appr.key vals 0, leaf pages 1, size pages 1
FIELDS: DB_ROW_ID DB_TRX_ID DB_ROLL_PTR id title user_id gmt_create gmt_modified
–在创建表时，没有定义主键，innodb会在内部创建一个主键索引
———————————-
END OF INNODB TABLE MONITOR OUTPUT
==================================
关于上面一些特殊字段中的含义
DB_TRX_ID – this field is managed by InnoDB internally and contains a ID of transaction which changed a record last time
DB_ROLL_PTR – one more internal InnoDB field (TODO: find out what is it used for).
DB_ROW_ID – this internally used field should be the first field in tables without primary keys (it is an auto-increment field used by InnoDB to identify rows in such tables)
test1表大小为5991 pages,与show table status like ‘test1′中的Data_length相比，数据计算证明完全相同
mysql> show table status like ‘test1′\G
*************************** 1. row ***************************
Name: test1
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 1573185 –这个是抽样值，不是精确值
Avg_row_length: 62
Data_length: 98156544
Max_data_length: 0
Index_length: 37339136
Data_free: 0
Auto_increment: 1572865
Create_time: 2009-06-22 12:37:17
Update_time: NULL
Check_time: NULL
Collation: gbk_chinese_ci
Checksum: NULL
Create_options:
Comment: InnoDB free: 871424 kB
1 row in set (0.00 sec)mysql> select 5991*16*1024;
+————–+
| 5991*16*1024 |
+————–+
| 98156544 |
+————–+
1 row in set (0.00 sec)
参考文档:
http://code.google.com/p/innodb-tools/wiki/InnodbRecoveryHowto