How Bad Statistics Cause Bad SQL Server Query Performance

SQL Server uses statistics to guess how many rows will match what your query is looking for. When it guesses too low, your queries will perform poorly because they won’t get enough memory or CPU resources. When it guesses too high, SQL Server will allocate too much memory and your Page Life Expectancy (PLE) will nosedive.

A common fix is to update your statistics regularly.

In this post, I’ll explain why bad stats cause bad performance, and give you some links on how to improve your statistics & performance.

When Statistics are Accurate…

Let’s start with a query against the