Sql-server – I have Fragmented Index on a empty table!

The tables are tiny. The page counts in your tables are:

11, 8, 6, 5, 13, 8, 10

They occupy 480kb in total. There is quite literally nothing to defrag.

Edit: This warrants a little more explanation.

A new table or index is usually allocated it's first 8 pages from a mixed, rather than uniform extent. So, it's possible for each of the first 8 pages to be allocated from different mixed extents. A table or index consuming 8 pages could therefore have 8 fragments, 1 on each of 8 different mixed extents.

The more widely used defrag scripts (a couple of examples linked below) tend to exclude small tables because of this. IIRC, <500 pages is in one or both of them. At these sizes, there is very little benefit to defragmenting and the fragmentation figures are potentially skewed by the mixed extent allocations.

• Ola Hallengren - SQL Server Maintenance Solution
• SQL Fool - Index Defrag Script

Updates on data already there causes rows to be moved and forward pointers added

In this test, we can get 65% fragmentation on 115k densely packed rows

CREATE TABLE #FragTest (
    FragTestID int NOT NULL IDENTITY PRIMARY KEY,
    SomeString varchar(4100) NULL
    );

INSERT #FragTest (SomeString) VALUES ('a');
GO
INSERT #FragTest (SomeString)
    SELECT F1.SomeString FROM #FragTest F1 CROSS JOIN #FragTest F2;
GO 4
INSERT #FragTest (SomeString) SELECT F1.SomeString FROM #FragTest F1    
GO 6

SELECT COUNT(*) FROM #FragTest

SELECT object_id, avg_fragmentation_in_percent, page_count
FROM sys.dm_db_index_physical_stats(2, OBJECT_ID('tempdb..#FragTest'), NULL, NULL, NULL);

UPDATE #FragTest
SET SomeString = REPLICATE('b', 4100)
WHERE FragTestID < 10000 AND FragTestID % 3 = 0

SELECT object_id, avg_fragmentation_in_percent, page_count
FROM sys.dm_db_index_physical_stats(2, OBJECT_ID('tempdb..#FragTest'), NULL, NULL, NULL);

UPDATE #FragTest
SET SomeString = REPLICATE('c', 4100)
WHERE FragTestID < 10000 AND FragTestID % 3 = 1

SELECT object_id, avg_fragmentation_in_percent, page_count
FROM sys.dm_db_index_physical_stats(2, OBJECT_ID('tempdb..#FragTest'), NULL, NULL, NULL);

UPDATE #FragTest
SET SomeString = REPLICATE('d', 4100)
WHERE FragTestID < 10000 AND FragTestID % 3 = 2

SELECT object_id, avg_fragmentation_in_percent, page_count
FROM sys.dm_db_index_physical_stats(2, OBJECT_ID('tempdb..#FragTest'), NULL, NULL, NULL);

Edit, sorry, browser trouble

If you change the middle replicate to 2000 you get <5% at the end. This happens because there is free space from moved rows in the first update