sp_BlitzIndex — ‘High value” vs ‘High Impact’

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Question :

Sorry, I may be missing something super-obvious here, but I’ve googled this and asked some colleagues and am not finding a satisfactory answer.

I’ve been using sp_BlitzIndex for a few months now along with some of my other regular index tuning tools and have found it to be a super-useful tool to add to my SQL toolbox.

But I do not quite understand the difference between ‘High value’ and ‘High Impact’ as in this example below:

‘Indexaphobia: High value missing index with High Impact’

At first I thought they meant roughly the same thing — it was identifying a missing index that would be both highly valuable and have a great impact on query performance.

But that didn’t quite make sense to me — why have two separate terms to indicate what was pretty much the same thing? So a colleague suggested that the term ‘impact’ was referring to the impact on db write operations. So ‘high impact’ in this case meant the index might cost more than other indexes when it came to updates and deletes.

But I’ve read some of Brent’s comments, and, if I’m understanding him correctly, I don’t think my colleague’s interpretation is quite right either.

Can someone please enlighten me on this? I’d really like to understand the difference before testing out some of the suggestions sp_BlitzIndex is making to me. Is ‘high impact’ good or bad? If it’s good, then what’s the difference between ‘high value’ and ‘high impact’?

Thanks very much in advance!!


Answer :

This finding in sp_BlitzIndex wasn’t really adding value, so we’ve removed “High Impact” altogether.

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