18Sep 2013 by Grant Fritchey 17 Comments

Finding Ad Hoc Queries with Query Hash

SQL Server, T-SQL
I was presenting a session on how to read execution plans when I received a question: Do you have a specific example of how you can use the query hash to identify similar query plans. I do, but I couldn't show it right then, so the person asking requested this blog post. If you're dealing with lots of application generated, dynamic or ad hoc T-SQL queries, then attempting to determine tuning opportunities, missing indexes, incorrect structures, etc., becomes much more difficult because you don't have a single place to go to see what's happening. Each ad hoc query looks different... or do they. Introduced in SQL Server 2008 and available in the standard Dynamic Management Objects (DMO), we have a mechanism to identify ad hoc queries that are similar in…
Read More
16Sep 2013 by Grant Fritchey 1 Comment

Why the Lazy Spool Is Bad

SQL Server, T-SQL
First thing, there are no bad operators, just bad parents, uh, I mean query writers, or database designers, or ORM tools. Why do I say this? Because all the operators within a query execution plan serve a purpose. They are there to fulfill a task. Depending on where and when you see them, they're doing exactly what you ask of them. The issues come up because you're asking them to do a task that they may not be well suited for. This comes from inappropriate structures and inappropriate code. Lazy spools are not really bad (that was just link bait). In fact, depending on the query, what's being done, how you're retrieving data, what data is being retrieved, the lazy spool is actually awesome. But, it's good to know what…
Read More
13Sep 2013 by Grant Fritchey 2 Comments

Are Foreign Keys Better Than Indexes?

SQL Server, T-SQL
When I first saw this question I thought to myself, "Self. Don't you think that's comparing apples to hammers? Yes, Self, I'm pretty sure it is. Good, I thought so too, self. Yeah, me too." After rebooting because of the runaway iterations on that thought, I had another, "Well... hold on there self. Both types of objects, while pretty different, are taken into account by the query optimizer." I then had to admit to myself that I had a point. So the question remains, are foreign keys better than indexes? As my first self said, these are different objects and they fulfill different purposes within SQL Server. My second self wants to point out that when you're dealing with functional objects within SQL Server, it's a bad habit to start…
Read More
11Sep 2013 by Grant Fritchey 2 Comments

Execution Plan Cost Estimates

SQL Server, T-SQL
It's been emphasized over and over that the costs of operations within an execution plan, and the estimated costs of the plan themselves are, in fact, estimates. But it goes further than that. The estimated values are based on statistics, or the lack thereof. Statistics themselves are also estimates. This means that the costs you're seeing are extrapolations based on extrapolations. So, you should just ignore those values and move on, right? Wrong. In order to understand how the optimizer is choosing to put together an execution plan for your query so that you can use that understanding to then make intelligent choices as to modifying the query or the structure of your database, you must use the values you have at hand. However, you must also understand where and…
Read More
05Sep 2013 by Grant Fritchey 7 Comments

sp_executesql, Parameters and Parameter Sniffing

SQL Server, T-SQL
I'm honestly not crazy about dynamic T-SQL within stored procedures. There are just a few too many opportunities to mess it up with dire circumstances to your server and your data. However, I absolutely recognize that dynamic T-SQL may be needed, and, in some situations, the best way to solve a problem. If you must use dynamic T-SQL, there are ways that are much more efficient than others. The very best thing you can do if you need to build dynamic strings to execute T-SQL in your stored procedures is use sp_executesql. The main reason I advocate for sp_executesql is because you can build out completely dynamic strings of T-SQL, but, you can still take advantage of parameters. Parameters help you avoid a chat with the parents of Bobby Tables…
Read More
28Aug 2013 by Grant Fritchey No Comments

Learn Query Tuning in Dallas

SQL Server, T-SQL
I am excited to be able to tell you about an all day seminar that I'll be putting on prior to the Dallas SQL Saturday #255. The seminar will be on November 1, 2013. It's called Query Performance Tuning in SQL Server. We're going to cover the topic from an understanding of the optimizer to collecting data using extended events to reading execution plans and then on to lots of standard problems and their solutions. If you sign up before September 21st you can get a substantial early-bird discount, so I'd jump on it. Also, seats are limited, so don't wait too long. Let's get together and talk query tuning.
Read More
05Aug 2013 by Grant Fritchey 19 Comments

Be Cautious Offering Guidance

Azure, SQL Server, T-SQL
Guidance is hard. Seriously, you'd think it would be easy. You'd think you say things like, don't shrink your database, most tables should have a clustered index, never go against a Sicilian when death is on the line, don't mix sharks and tornados, and that would be it. You'd be done. But it's not that easy. Even worse, it's SHOCKINGLY easy to get stuff wrong. An example. I was looking at information over at Microsoft Developers Network (MSDN) in the SQL Server Books Online. I was reading through information about wait types when I found this little beauty: Occurs when trying to synchronize the query processor exchange iterator. Know what that is? Yeah, OK, a few of you who memorize wait stats do (shut up Tom), but most of us…
Read More
04Jun 2013 by Grant Fritchey 4 Comments

Helping Database Administrators

Redgate Software, SQL Server
Let's be honest. Database administration is not all that tough. Set up your backups. Test them. Get consistency checks on line. Some maintenance routines for statistics and maybe for fragmentation are also helpful. Set up security. In most of the important ways, you're done. Sit back, monitor the whole thing and collect your paycheck. BWA-HA-HA! Yeah, well, it's a nice dream. The reality is that you're dealing with constant change that throw this simple set of maintenance monitoring tasks into the garbage. No, you've got new databases under development. Sometimes by development teams that are absolute rocket scientists and you sit at their feet learning how they did some really cool piece of code. And sometimes by development teams that more resemble crazed monkeys throwing poo at the walls to…
Read More
03Jan 2013 by Grant Fritchey No Comments

SQLBits Public Sessions

SQL Server
If you're over in the UK, or close to it, you've probably heard of SQL Bits even if you haven't attended. If you're across the pond here in the US or somewhere else you may have heard of SQL Bits, but few of you have gone. Well, let me tell you, from everything I've heard, this is a community event you want to find your way to. So, I'm trying. This is my first time submitting to this outstanding event and I really want to go. But, in order to make the cut, I need your help. They base who presents on community feedback. This means you go over and vote. You'll have to have a SQL Bits login, but if you're even thinking about attending you're going to have…
Read More
30Nov 2012 by Grant Fritchey 2 Comments

Sharing the Love

SQL Server, T-SQL
Just a few blog posts that you ought to go and read. First up, Tom LaRock maintains a listing of SQL bloggers split up into various cleverly named groups to show you where to go to get good information. This really is an excellent collection of bloggers. It's the people I go to when I need information. Some of them are better resources than the Books Online when they post something. Personally, I've made the list for the last several years, but Tom has decided that I'm worth of elevation, so I've gone from the Model database to the Master database. Thanks Tom. One blog that's not on Tom's list is Tom's blog. You should be reading that regularly too. And congratulations to Tom again on making MCM. Next, one…
Read More