Execution Plan Metrics and Units of Measure

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, SQL Server 2017
Have you ever looked at the properties inside an execution plan and wondered what the units of measure were? I know I have. I also get the question pretty frequently about all sorts of properties. What does EstimatedAvailableMemoryGrant display it's units in anyway? For that matter, what the heck is an EstimatedAvailableMemoryGrant? Showplan Schema and Units of Measure The answer to those questions and a whole lot more is pretty easy to find. You just have to look to the ShowPlan Schema. Microsoft has all the schema's published, going back to 2005. The next time you're faced with a question such as, what are the units of measure of the MemoryGrantInfo: Or, what the heck is SerialDesiredMemory and why is it exactly matching RequestedMemory, you just have to go and…
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Why I Use AdventureWorks for Demos

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, SQL Server 2017
I know that when some people see AdventureWorks, their vision turns all red around the edges, their blood pressure spikes and they begin to foam at the mouth. I do understand. AdventureWorks, Microsoft's very old, near ubiquitous, sample database suffers from a lot off issues. What's The Matter With AdventureWorks? Let's start off with the general design of the schemas. It's broken up in odd ways. Production has a TransactionHistory and a TransactionHistoryArchive instead of Sales? That doesn't make any sense. What the heck is up with the general database design anyway? I mean, pick on one example. A person can have more than one phone number. Fine. But, what about people who share phone numbers like that ancient land line in my house that is only EVER used by…
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Database Fundamentals #15: Modifying Data With T-SQL

Database Fundamentals, SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, SQL Server 2017
The preferred method for modifying your data within a database is T-SQL. While the last Fundamentals post showed how to use the GUI to get that done, it's not a very efficient mechanism. T-SQL is efficient. UPDATE The command for updating information in your tables is UPDATE. This command doesn’t work the same way as the INSERT statement. Instead of listing all the columns that are required, meaning columns that don’t allow for NULL values, you can pick and choose the individual columns that you want to update. The operation over-writes the information that was stored in the column with new information. In addition to defining the table and columns you want to update, you have to tell SQL Server which rows you’re interested in updating. This introduces the WHERE…
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Bad Parameter Sniffing Decision Flow Chart

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016
Lots of people are confused by how to deal with bad parameter sniffing when it occurs. In an effort to help with this, I'm going to try to make a decision flow chart to walk you through the process. This is a rough, quite rough, first draft. I would love to hear any input. For this draft, I won't address the things I think I've left out. I want to see what you think of the decision flow and what you think might need to be included. Click on it to embiggen. Thanks to the attendees at my SQLSaturday Louisville pre-con for the great questions and the inspiration to get this done. Thank you in advance for any and all feedback.
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There Is a Magic Button, a Rant

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, TSQL
OK guys. I think it's way past time. A bunch of us have been keeping a secret from the rest of you. We know something that you don't. I don't think we should hide this secret from the world any more. Illuminati? Incompetents. Free Masons? I am one, so I already know all those secrets. Bilderbergers, Cthulhu Cultists, MKUltra, New World Order, Rotarians? All of these are nothing compared to the vast conspiracy that I'm about to reveal. We need to just unveil the magic "Run Really Fast" button. We've been keeping that sucker a secret forever. It's been tough. Every so often some unauthorized person almost finds it or a "query tuning expert" (as if that was a real thing) tries to reveal it. But we've kept it secret…
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Why You Should Change the Cost Threshold for Parallelism

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016
I've written several times about the Cost Threshold for Parallelism and it's relationship to your execution plans, how to determine your execution plan cost, and even how to decide what value to set your Cost Threshold to. What I haven't explicitly addressed in extremely clear terms is why you should adjust your Cost Threshold for Parallelism. There are two reasons to modify this value. Cost Threshold for Parallelism Default Value The primary reason to change the Cost Threshold for Parallelism is because the default value is not a good choice for the vast majority of systems. The default value is 5. This means that when a query has an estimated cost greater than 5, it may get a parallel execution plan. Microsoft set the default value for the Cost Threshold…
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Determining the Cost Threshold for Parallelism

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016
In the previous post, I showed how you can get full listings of your execution plan costs. Knowing what the values you're dealing with for the estimated costs on your execution plans can help you determine what the Cost Threshold on your system should be. However, we don't want to just take the average and use that. You need to understand the data you're looking at. Let's explore this just a little using R. Mean, Median, Range and Standard Deviation I've used the queries in the previous blog post to generate a full listing of costs for my plans. With that, I can start to query the information. Here's how I could use R to begin to explore the data: [crayon-5a70520f96afa440158554/] The mean function is going to get me my…
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Estimated Costs of All Queries

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016
One question constantly comes up; What should the Cost Threshold for Parallelism be? The default value of 5 is pretty universally denigrated (well, not by Microsoft, but by most everyone else). However, what value should you set yours to? What Do Your Plans Cost? I have a question right back at you. What do your plans currently cost? Let's say, for argument's sake, that all your plans have an estimated cost (and all plan costs are estimates, let's please keep that in mind, even on Actual plans) value of 3 or less. Do you need to adjust the cost threshold in this case? Probably not. But the key is, how do you look at the costs for your plans? Unfortunately, there isn't a property in a DMV that shows this value. Instead,…
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Data About Execution Plans

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016
If you look at the Properties for the first operator of a graphical execution plan, you get all sorts of great information. I've talked about the data available there and how important it is in this older post. Checking out the properties of a plan you're working on is a fundamental part of tuning that plan. What happens when you don't know which plan you should be working on? What do you do, for example, if you want to see all the plans that are currently using ARITHABORT=FALSE or some other plan affecting setting? The "easy" answer to this question is to run an XQuery against the XML of the query plan itself. You can identify these properties and retrieve the appropriate values from within the plan. However, XQuery consumes quite a…
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Query Optimizer and Data Definition Language Queries

SQL Server 2005, SQL Server 2008, SQL Server 2012, SQL Server 2014, SQL Server 2016, TSQL
Data Definition Language queries don't go through the optimizer, right? While normally, my short answer to this question in the past would have been, yes. However, with testing comes knowledge and I want to be sure about the statement. I'm working with a team of people to completely rewrite the SQL Server Execution Plans book. We'll probably be published in April or May. It's going to be amazing. The structure will be completely different and the book will represent five years of additional knowledge in how execution plans work and how to read and interpret them since the last book was written. However, enough on that. Let's answer the question about Data Definition Language. First of all, we need to quickly define our terms. Data Definition Language (DDL) represents the syntax for queries that build…
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