--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)