performance-tuning

Estimated vs. Actual Number of Rows in Nested Loop Operators

Estimated vs. Actual Number of Rows in Nested Loop Operators

This is one of those little details that confused me a ton when I was first working with execution plans.

One problem with learning to work with plans is that there’s just SO MUCH to look at. And it’s a bit spread out. So, even when looking at a single tooltip, things can be confusing.

Let’s talk about the nested loop operator, who can be particularly weird to understand.

Live Query Statistics Don't Replace Actual Execution Plans

Live Query Statistics Don't Replace Actual Execution Plans

I like SQL Server’s new Live Query Statistics feature a lot for testing and tuning large queries. One of my first questions was whether this could replace using actual execution plans, or if it’s useful to use both during testing.

Finding: Both are useful. And both can impact query performance.