关于sp_BlitzIndex中“High value”与“High Impact”的区别咨询

Great question—this is such a common point of confusion with sp_BlitzIndex, especially since those two labels sound interchangeable at first glance. Let’s break down exactly what each one means, using plain language and real-world examples:

What "High Value" Indicates #

High Value is all about the magnitude of performance gain you’d get by creating the missing index. It’s calculated based on three key factors:

• The average resource cost (CPU, IO, runtime) of the queries that would use the index
• The estimated percentage improvement those queries would see if the index existed
• How often those queries have been executed

In short: This index would deliver massive per-query performance improvements. For example, imagine a weekly sales report query that scans 50GB of data and takes 90 minutes to run. Creating the right missing index could cut that runtime down to 5 minutes—that’s high value, even though it only runs once a week.

What "High Impact" Indicates #

High Impact focuses on the breadth of queries affected by the missing index. It’s driven primarily by the total number of times queries have looked for this index (sum of seek and scan operations that would have used it).

This label tells you: A large number of queries (or extremely frequent queries) are being slowed down because this index doesn’t exist. For instance, a customer lookup query that runs 2,000 times per second on your e-commerce site. Each individual query might only save 10ms with the index, but over the course of a day, that adds up to hours of saved server resources—making this high impact.

When You See Both: "Indexaphobia: High value missing index with High Impact" #

This combination is your top priority for index creation. It means:

• You’ll get huge performance gains per query (high value)
• And hundreds or thousands of queries are waiting for that improvement (high impact)

Fixing this index will quickly make a tangible difference to your server’s overall performance—this is the low-hanging fruit you don’t want to ignore.

内容的提问来源于stack exchange，提问作者Robert H