行大小计算测试

数据库中每一行到底占用多少空间，在这里，做个小测试~~~这里只做了堆表的计算，如果包含索引，按照文档把索引的列也加上就OK啦~

建个测试表，然后用DBCC PAGE打印出Slot的信息

CREATE TABLE TstA( col1 CHAR(5) NULL, col2 CHAR(5) NULL, col3 VARCHAR(5) NULL, col4 VARCHAR(10) NULL, col5 VARCHAR(50) NULL)INSERT INTO TstA (col1,col2,col3,col4,col5) VALUES ('aa1','2222222222','joan2','aoaonfoen','1111111')dbcc ind(TestDB, Object_id('TstA'),-1) 

DBCC PAGE(TestDB,1,11957,1)

然后我就直接把slot的消息贴出来分析吧~~

-------------------------------------------------------------------------------------------------------------------------------------

Slot 0, Offset 0x60, Length 51, DumpStyle BYTE

Record Type = PRIMARY_RECORD Record Attributes = NULL_BITMAP VARIABLE_COLUMNS

Record Size = 51

Memory Dump @0x0A93C060

00000000: 30000e00 61613120 206a6f61 6e320500 †0...aa1 joan2..

00000010: 00030023 002c0033 00323232 32323232 †...#.,.3.2222222

00000020: 32323261 6f616f6e 666f656e 31313131 †222aoaonfoen1111

00000030: 313131†††††††††††††††††††††††††††††††111

4 8 12 16 20 24 28 32 36 40 44 48 52

30000e0061613120 206a6f61 6e32050000030023 002c0033 00323232 323232332323261 6f616f6e 666f656e31313131313131

1 2 3 4 5 6 7 8 9

1： 固定长度列结束位置

2： 固定长度第一列(col1)

3： 固定长度第二列(col3) --如果之后还有更多的列，继续往后排

4： 行包含的栏位总数，本例为5

5： 空值维护：计算方式为 2+ (可为空列数+7)/8

6： 每一个可变列的结束位置。长度计算 2 + (可变列列数*2)

7+：变长列的每一个填充列

验证了这一句话，每行的开销

• ix bytes per row for status information and length information.
• One bit per fixed width column, rounding up to the nearest byte.
• If there are any variable length columns - four bytes for the first, plus two bytes for each additional variable length column
• An additional two bytes per row for the offset pointer located at the end of the page.

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经过测试，无论列的顺序怎么排，首先会先把定长的字段先排出来，然后再排变长字段~好吧~测试结束

小弟不才~欢迎大家指出不足

参考：

　　http://technet.microsoft.com/zh-cn/library/ms189124.aspx

PS：上面2个DBCC 的语法

dbcc page ( {'dbname' | dbid}, filenum, pagenum [, printopt={0|1|2|3} ])

The filenum and pagenum parameters are taken from the page IDs that come from various system tables and appear in DBCC or other system error messages. A page ID of, say, (1:354) has filenum = 1 and pagenum = 354.

The printopt parameter has the following meanings:

0 - print just the page header1 - page header plus per-row hex dumps and a dump of the page slot array (unless its a page that doesn't have one, like allocation bitmaps)2 - page header plus whole page hex dump3 - page header plus detailed per-row interpretation