DBCC showcontig Parameters

Original article:Http://www.cnblogs.com/petitprince/archive/2009/10/23/1588603.html

DBCC showcontig is used to display the data and index fragmentation information of a specified table.

Explanation:

Page scanned-Number of scanned pages: If you know the approximate size of the rows and the number of rows in the table or index, You can estimate the number of pages in the index. Look at the number of scanned pages. If it is significantly higher than your estimated number of pages, it indicates there are internal fragments.

Extents scanned-Number of scanned extended disk partitions: divided by the number of scanned pages by 8, rounded to the next maximum value. This value should be consistent with the number of scan extended disk areas returned by DBCC showcontig. If the number returned by DBCC showcontig is high, external fragments exist. The severity of fragments depends on the value displayed just now, which is higher than the estimated value.

Extent switches-Number of switches in the extended Disk Area: this number should be equal to the number of scanned extended disk areas minus 1. If it is high, external fragments exist.

AVG. pages per extent-average page number on each extended Disk Area: this is the number of scanned pages divided by the number of scanned extended disk areas, usually 8. If the value is smaller than 8, external fragments exist.

Scan density [best count: actual count]-scan density [Best Value: actual value]: DBCC showcontig returns the most useful percentage. This is the ratio of the Best Value of the extended disk to the actual value. The percentage should be close to 100% as much as possible. If it is low, external fragments exist.

Logical scan fragmentation-logical scan fragmentation: Percentage of unordered pages. The percentage should be between 0% and 10%. If the percentage is high, external fragments exist.

Extent scan fragmentation-extended Disk Area scan fragmentation: the percentage of unordered extended disk areas that scan index leaf pages. The percentage should be 0%. If the percentage is high, external fragments exist.

AVG. bytes free per page-average number of available bytes per page: the average number of available bytes on the scanned page. The higher the description, the more internal fragments are. But before you use this number to determine whether there are internal fragments, consider the fill factor ).

AVG. Page density (full)-average page density (complete): the opposite of the percentage of average available bytes per page. A low percentage indicates that internal fragments exist.