Indexes On Disk

Kendra Little has a great diagram showing which indexes are disk-based and which are memory-resident:

I was looking through some terms in SQL Server documentation the other day, thinking about what it’s like to learn about SQL Server’s indexes when you’re new to the field. I jotted down a note: B-tree = Rowstore = Disk Based

And then I realized that’s not quite right.

Not all disk based indexes are traditional clustered and nonclustered indexes. Columnstore indexes are also disk based. Updatable Columnstore indexes use special rowstore B-trees behind the scenes. And Books Online says “rowstore” also refers to Memory-Optimized tables.

If you’re new to indexing, this picture will save you some learning time.

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