InnoDB与Oracle单行存储长度对比

众所周知,MySQL InnoDB存储引擎与Oracle非常相似,支持事务,row-locking,经过实际测试,innodb与oracle一个比较大的差异点为,相

众所周知,MySQL InnoDB存储引擎与Oracle非常相似,支持事务,row-locking,经过实际测试,innodb与oracle一个比较大的差异点为,相同数据,innodb单行存储长度大概是oracle单行存储长度的1.8倍。
测试的表,常见的各种类型都有,number,varchar2,date

--首先在Oracle中做测试 , 在Oracle数据库中此表单行长度平均为458字节

09:49:45 danchen@ test_oracle>select blocks from dba_extents where segment_name='test_dc' and rownum<2;

BLOCKS
----------
1280

1 row selected.

09:52:55 danchen@ test_oracle>select /*+ rowid(u)*/ count(*) from test_dc u where rowid>=CHARTOROWID('AAADQdAA6AAADcJAAA') and rowid<=CHARTOROWID('AAADQdAA6AAADwICcQ');

COUNT(*)
----------

22852

09:54:55 danchen@ test_oracle>select 1280*8*1024/22852 bytes from dual;

BYTES
----------
458.855242

--在mysql作对比测试
root@test_mysql 09:47:47>select count(*) from test_dc_181;
+----------+
| count(*) |
+----------+
| 128928 |
+----------+
1 row in set (0.08 sec)

root@test_mysql 09:45:57>show table status like 'test_dc_181'\G;
*************************** 1. row ***************************
Name: test_dc_181
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 85668 --统计信息不准确
Avg_row_length: 1122
Data_length: 96141312
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2009-05-27 11:23:55
Update_time: NULL
Check_time: NULL
Collation: gbk_chinese_ci
Checksum: NULL
Create_options:
Comment: InnoDB free: 292984832 kB
1 row in set (0.00 sec)

ERROR:
No query specified


--重新分析一下,发现执行分析操作时间非常快,数据也比较准确,估计mysql的分析的算法原理为基于抽样的统计,比如说一个page里有多少记录,,总的page数是多少,两者相乘即可得到行数。
root@test_mysql 09:46:01>analyze table test_dc_181;
+---------------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+---------------------+---------+----------+----------+
| test_mysql.test_dc_181 | analyze | status | OK |
+---------------------+---------+----------+----------+
1 row in set (0.00 sec)

root@test_mysql 09:46:46>show table status like 'test_dc_181'\G;
*************************** 1. row ***************************
Name: test_dc_181
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 115074
Avg_row_length: 835
Data_length: 96141312
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2009-05-27 11:23:55
Update_time: NULL
Check_time: NULL
Collation: gbk_chinese_ci
Checksum: NULL
Create_options:
Comment: InnoDB free: 292984832 kB
1 row in set (0.00 sec)

ERROR:
No query specified

--在mysql innodb的表中平均单行长度为835字节

root@test_mysql 09:46:50>select 96141312/115074;
+-----------------+
| 96141312/115074 |
+-----------------+
| 835.4738 |
+-----------------+
1 row in set (0.00 sec)


--同一行记录,在oracle与mysql存储空间对比为1.8:1,所以在做容量估计的时候要注意。
root@test_mysql 09:48:14>select 835.4738/458.855242 ;
+---------------------+
| 835.4738/458.855242 |
+---------------------+
| 1.82077859 |
+---------------------+
1 row in set (0.00 sec)

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