InnoDB與Oracle單行儲存長度對比

眾所周知，MySQL InnoDB儲存引擎與Oracle非常相似,支援事務，row-locking,經過實際測試，innodb與oracle一個比較大的差異點為，相同資料，innodb單行儲存長度大概是oracle單行儲存長度的1.8倍。
測試的表，常見的各種類型都有,number,varchar2,date

--首先在Oracle中做測試 , 在Oracle資料庫中此表單行長度平均為458位元組

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作對比測試
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   --統計資訊不準確
 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,發現執行分析操作時間非常快，資料也比較準確，估計mysql的分析的演算法原理為基於抽樣的統計，比如說一個page裡有多少記錄，總的page數是多少,兩者相乘即可得到行數。
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的表中平均單行長度為835位元組

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

--同一行記錄，在oracle與mysql儲存空間對比為1.8:1,所以在做容量估計的時候要注意。
root@test_mysql 09:48:14>select 835.4738/458.855242 ;
+---------------------+
| 835.4738/458.855242 |
+---------------------+
|          1.82077859 |
+---------------------+
1 row in set (0.00 sec)