Sqldatabase fragment check DBCC showcontig meaning

Source: Internet
Author: User

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

As shown in.


Page scanned-Number of scanned pages: If you know the approximate size of 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: Divide by the number of scanned pages 8, Rounding to the next maximum value. This value should be consistent DBCC showcontig The number of scanned extended disk areas returned is the same. If DBCC showcontig The returned number is high, indicating that 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 in each extended Disk Area: This number is the number of scanned pages divided by the number of scanned extended disk areas, usually 8 . Less 8 It indicates that external fragments exist.
Scan density [best count: actual count]-scan density [optimal 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. This percentage should be as close as possible 100 %. If it is low, external fragments exist.

Logical scan fragmentation-logical scan fragmentation: Unordered page percentage. The percentage should be in 0 % 10 %. If it is higher, it indicates there are external fragments.
Extent scan fragmentation-extended Disk Area scan fragments: The percentage of unordered extended disk areas on the scanned index leaf page. The percentage should be 0 %. If it is higher, 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. However, before using this number to determine whether internal fragments exist, considerFill Factor (Fill factor ).
AVG. Page density (full)-average page density (complete ): Flat on each page The opposite of the percentage of the number of nodes. A low percentage indicates that internal fragments exist.


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