Sql-server – Database Space Used Decreased after Index Rebuild (Ola Script)

database-sizeindex-tuningola-hallengrensql serversql-server-2012

I have rebuilt some indexes which were highly fragmented. After the index rebuild I am seeing my database space used reduced by almost 50% (from 77gb to 33 gb)

Is that normal behavior? I dont have auto shrink turned on – did I lose data?

Note: space used decreased in my database file; the actual physical size of my database file is unchanged.

Command used to calculate the space used:

SELECT sum(CAST(FILEPROPERTY(name, ''SpaceUsed'') AS INT))/128.0 as Space_Used_MB

Results of select @@version

Microsoft SQL Server 2014 (SP2-CU11) (KB4077063) – 12.0.5579.0 (X64)

Rebuild of indexes performed using Ola Hallengren's script. Parameters used:

Databases = 'USER_DATABASES',
FragmentationMedium='INDEX_REORGANIZE,INDEX_REBUILD_ONLINE,INDEX_REBUILD_OFFLINE 
',
FragmentationHigh = 'INDEX_REBUILD_ONLINE,INDEX_REBUILD_OFFLINE', 
FragmentationLevel1 = 5, FragmentationLevel2 = 30, FillFactor=80, 
UpdateStatistics = 'ALL', OnlyModifiedStatistics = 'Y', LogToTable = 'Y'" -b

Best Answer

You would not lose data with index maintenance / rebuilds. As your data is fragmented, the data would be spread over multiple leaf pages in the clustered / nonclustered indexes as data is deleted / updated over time leaving empty space in the page position where it was originally. Reorganizing / rebuilding the index recovers the space by reordering the data in the pages and releasing the space back to the database for future use.

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