Chapter 40. When is an unused index not an unused index?
Rob Farley
Indexes can help you access your data quickly and effectively, but index overhead can sometimes be costly. Keeping an index updated when data is changing is one cost, but there is also the cost of extra storage space and the increased size of backups. So if an index isn’t being used, you should remove it, right?
In this chapter, I’ll show you ways to find out if an index is used. Then I’ll show you a type of index that may appear to be unused even although it really is used. Hopefully this won’t leave you too disheartened about the idea of researching your indexes but instead convince you of the power of SQL Server.
My favorite analogy for indexes is telephone directories. I’m not sure whether I heard this analogy or came up with it—I just know that it’s a way of describing indexes that everyone grasps easily. Like most analogies, it doesn’t fit completely, but on the whole it’s fairly good.
