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rhandloff (3) [Avatar] Offline
The index related DMV queries are extremely useful but it would have been nice to know more about certain key columns such as avg_user_impact. What does this column actually measure? What are the units of measure? Stuff like that.
ian.stirk (27) [Avatar] Offline
Re: More information on Index related DMVs

Thanks for your message.

The aim of the code snippets is to target areas for improvement. This can be achieved without knowing the details of each specific column (similarly, it is possible to be a good driver without knowing how the car’s engine works). I basically say avg_user_impact is a measure of query improvement. The column avg_user_impact is a percentage, so doesn’t have a unit.

That said, it is possible to get details of the DMV columns in SQL Server Books Online, which defines avg_user_impact as: Average percentage benefit that user queries could experience if this missing index group was implemented. The value means that the query cost would on average drop by this percentage if this missing index group was implemented.

I will try to include this in the chapter.


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