Question

I’ve spent some time researching this and simply can’t find a definitive answer. Here is the query I am using to look for indexes not used:

SELECT object_name(i.object_id) as tableName, i.name as indexName
FROM sys.indexes i
LEFT JOIN sys.dm_db_index_usage_stats s ON i.object_id = s.object_id AND i.index_id = s.index_id AND s.database_id = db_id()
WHERE objectproperty(i.object_id,'IsUserTable') = 1 and i.index_id> 0
AND s.object_id IS NULL
AND i.is_Primary_Key = 0
AND i.is_unique_constraint = 0
AND i.is_unique = 0

My understanding is that indexes returned by this query have not been utilized by the query optimizer since sql server was last restarted. I believe I should remove them….I just don’t fully understand if there are performance implications or harm in leaving them.

Answer 1

The harm of leaving them in is the space used and the increased work for INSERT, UPDATE and DELETE statements as they have to keep the indexes updated as well as the base table.