索引数据行大小不返回实际大小？

CREATE TABLE dbo.overhead ( myID INT NOT NULL ) ;

CREATE CLUSTERED INDEX CIX_overhead -- not unique!
ON dbo.overhead(myID) ;

INSERT  INTO dbo.overhead
        ( myID )
        SELECT  1 ;


SELECT  min_record_size_in_bytes ,
        max_record_size_in_bytes

FROM    sys.dm_db_index_physical_stats(DB_ID(), OBJECT_ID(N'dbo.overhead'),

                                       NULL, NULL, N'SAMPLED') ;



min_record_size_in_bytes   max_record_size_in_bytes

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

25                         25

It should give 4 bytes as INT record 1 row is inserted, why 25?

当插入INT记录1行时,它应该给4个字节,为什么25?

1 个解决方案

#1

4 bytes for the record header

记录头的4个字节

4 bytes for the int

int的4个字节

2 bytes for the count of columns in the null-bitmap

空位图中列数的2个字节

1 byte for the null bitmap

空位图为1个字节

14 bytes versioning tag because you have snapshot isolation enabled (or are using MARS)

14字节版本标记,因为您启用了快照隔离(或正在使用MARS)

That's 25 bytes in total. There are also 2 additional bytes for the slot pointer at the bottom of the page, but those are not accounted for in the DMV.

这总共是25个字节。页面底部的插槽指针还有2个额外字节,但DMV中不考虑这些字节。

Source: http://www.sqlskills.com/blogs/paul/inside-the-storage-engine-anatomy-of-a-record/

#1

4 bytes for the record header