The Value Of Statistics In SQL Server

Monica Rathbun walks us through the benefits of having statistics on tables in SQL Server:

Statistics are made up of three parts. Each part tells the optimizer important information regarding the make up the table’s data distribution.

Header – Last Time Stats were updated and number of sample rows

Density Vector – Uniqueness of the columns or set of columns

Histogram– Data’s distribution and frequency of distinct values

Let’s look at a Header, Density and Histogram example.

You can read what the statistic are broken down into using DBCC SHOW_STATISTICS. All field definitions are taken from MSDN.

This is from AdventureWorks2016CTP3 sample database, if you want to follow along. Using the Sales. SalesOrderDetail table let’s look the stats and see what we can find out what it shows us.

Read the whole thing.

Related Posts

Troubleshooting Query Performance Changes

Erin Stellato walks us through a troubleshooting guide when users complain about poorly-performing queries: This is tale of troubleshooting… When you unexpectedly or intermittently encounter a change in query performance, it can be extremely frustrating and troublesome for a DBA or developer. If you’re not using Query Store, a third-party application, or your own method […]

Read More

Workarounds for Updating Stats on Secondaries

Niko Neugebauer wants statistics updates on tables running on readable Availability Group secondary nodes: Let’s list the basic known details for the possible solution(for the Enterprise Edition of the Sql Server that is):– We can make the secondary replica readable and read the same data on it. (Not that you should do that by default, […]

Read More

Categories

May 2018
MTWTFSS
« Apr Jun »
 123456
78910111213
14151617181920
21222324252627
28293031