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I recently found out that turning on nolock is a horrible idea. It doesn't just take you out of transactions. That is, you won't just get uncommitted data, but apparently can get completely inconsistent data as internal structures are updated. That is, even rows not part of a current transaction might not be seen, if you use nolock.

Edit: Turning ON nolock, that is.

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My experience with nolock is that you may get inconsistent rows with some fields before and some after update. Or even seeing duplicated rows when b-tree is rebalanced. But I never seen single fields being partially updated. Per Microsoft, page latch protects atomicity of a single field update. This is why nolock was extremely useful for insert-only tables and in our database design we had many of them.

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