10Oct 2016 by Grant Fritchey 2 Comments

Statistics Are Vital For Query Performance

SQL Server, SQL Server 2016
This is post #10 supporting  Tim Ford’s (b|t) initiative on #iwanttohelp, #entrylevel. Read about it here. When you send a query to your SQL Server database (and this applies to Azure SQL Database, APS, and Azure SQL Data Warehouse), that query is going to go through a process known as query optimization. The query optimization process figures out if you can use indexes to assist the query, whether or not it can seek against those indexes or has to use a scan, and a whole bunch of other stuff. The primary driving force in making these decisions are the statistics available on the indexes and on your tables. What Are Statistics Statistics are a mathematical construct to represent the data in your tables. Instead of scanning through the data each and every…
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22Aug 2011 by Grant Fritchey 3 Comments

Expert? Ha!

SQL Server, T-SQL
How do you define an expert? My personal definition: An expert is the person that is a chapter ahead of you in the book. Why am I talking about this? Just that I’m feeling more stupid than usual lately. In the last two weeks I’ve had people bring up through various discussions, documents, what have you, four different SQL Server trace flags that will affect how SQL Server builds execution plans and I’ve never heard of any of them before. I’ve never, ever, thought of myself as an expert in execution plans, despite having written a book about them. I just thought I had a good grasp on how they worked and I was willing to share. I didn’t know everything and never pretended to, but I thought I knew…
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30Nov 2010 by Grant Fritchey 6 Comments

Regressions

SQL Server
[caption id="" align="alignleft" width="244" caption="Hannah Dustin, Upset about Regression"][/caption] One of the most important take-aways from David Dewitt's presentation at the PASS Summit was the level of fear within the Query Processing team at Microsoft caused by regressions. If you missed Dr. Dewitt's presentation, I tried to capture as much of it as I could here, and it will be available within the DVDs from PASS. Regression is when something moves backwards to a less perfect state. When talking about the optimizer in SQL Server, a regression is when you see a query that used to run fast in SQL Server 2000 or 2005 and suddenly after upgrading to 2005 or 2008, the exact same query now generates a different execution plan and runs slowly. Now do you know why…
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18Nov 2010 by Grant Fritchey 18 Comments

Reason for Early Termination of Statement

SQL Server, T-SQL
Wouldn't you like to know why the optimizer stopped tuning the execution plan you're looking at? It's actually possible and simple to get this information. I talked about this a little more than a year ago, but I left out some information that might be useful. Let's take a very simple query: SELECT * FROM Person.Address AS a; This generates a simple execution plan, in fact a trivial plan: I know that this is a trivial plan one of two ways. The hard way is to look at the XML (BTW, this is the type of thing you can't see it in STATISTICS PROFILE, which I understand a lot of people are using). Right at the top is the SELECT element. You can see the value for StatementOptmLevel property is…
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26Oct 2010 by Grant Fritchey 1 Comment

New Book on Query Optimizer

Uncategorized
Benjamin Nevarez (blog) has been working really hard on a book on the Query Optimizer. It just got finished in time so that there will be copies available at the PASS Summit. I strongly recommend you track it down. There's a lot to learn between the covers. How do I know since the book just got finished and isn't in anyone's hands yet? Because I've been watching it get built. I put in my small efforts as the technical editor. I feel bad about that because I've always learned from my technical editors and I'm fairly sure I learned more from Benjamin than he did from me. Get a copy of the book. You won't be disappointed.
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