MS SQL Server Interview Question:

How To Defragment Indexes with ALTER INDEX ... REORGANIZE?

Submitted by: Administrator

When an index is defragmented to a small percentage, like < 30%, you can use the "ALTER INDEX ... REORGANIZE" statement to defragment the index. Here is a tutorial exercise on defragmenting indexes:

SELECT i.index_id, i.name, s.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (
DB_ID(N'GlobalGuideLineDatabase'),
OBJECT_ID(N'ggl_links_indexed'),
DEFAULT, DEFAULT, DEFAULT) s, sys.indexes i
WHERE s.object_id = i.object_id
AND s.index_id = i.index_id;
GO
0 NULL 0.574712643678161
2 ggl_links_url 84.053862508859
3 ggl_links_counts 0.448430493273543

ALTER INDEX ggl_links_url ON ggl_links_indexed REORGANIZE;
GO
SELECT i.index_id, i.name, s.avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (
DB_ID(N'GlobalGuideLineDatabase'),
OBJECT_ID(N'ggl_links_indexed'),
DEFAULT, DEFAULT, DEFAULT) s, sys.indexes i
WHERE s.object_id = i.object_id
AND s.index_id = i.index_id;
GO
0 NULL 0.574712643678161
2 ggl_links_url 1.87590187590188
3 ggl_links_counts 0.448430493273543

The fragmentation level has been reduced from 84.05% to 1.88%.
Submitted by: Administrator