07Feb 2017 by Grant Fritchey 4 Comments

Does Query Store Pre-Allocate Space

SQL Server 2016, T-SQL
I love the questions I get while I'm presenting because they force me to think and learn. The question in the title is one I received recently. The answer, now that I'm not standing in front of people, is easy. Of course the space is not pre-allocated. Query Store tables are just system tables. They have a limit on how big they can grow (100mb by default), but that space isn't going to be pre-allocated in any way. The space will just get used as and when it's needed, just like any other system table. However, don't take my word for it, let's prove that. The Test Testing whether or not enabling Query Store is straight forward. Here's a query that should give us information rather quickly: CREATE DATABASE QSTest; GO USE…
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10Jan 2017 by Grant Fritchey 3 Comments

Query Optimizer and Data Definition Language Queries

SQL Server, SQL Server 2016, T-SQL
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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20Dec 2016 by Grant Fritchey 1 Comment

Database Configuration

Azure, SQL Server 2016
It's amazing just how much the landscape changed with the release of SQL Server 2016 SP1. For example, I just found out that you can disable parameter sniffing at the database level using the database configuration. Not only does this work for SQL Server 2016 SP1, but it's enabled for Azure SQL Database. How Database Configuration Works The syntax is very simple and documented here. So, if I want to disable parameter sniffing for a single database, I can do this: ALTER DATABASE SCOPED CONFIGURATION SET PARAMETER_SNIFFING = OFF; That's it. Done. It works from within the database and doesn't require rebooting or anything else. Changing this setting does flush the cache of all the execution plans for that database. No other actions are necessary. You can control parameter sniffing at the…
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12Dec 2016 by Grant Fritchey 7 Comments

OPTIMIZE FOR Hints When Parameter Sniffing is Turned Off

Azure, SQL Server, SQL Server 2016, T-SQL
While presenting recently and talking about dealing with bad Parameter Sniffing, I got the question; what happens to OPTIMIZE FOR hints when parameter sniffing is disabled? This is my favorite kind of question because the answer is simple: I don't know. Parameter Sniffing For those who don't know, parameter sniffing is when SQL Server uses the precise values passed into a query as a parameter (this means stored procedures or prepared statements) to generate an execution plan from the statistics using the value from the parameter. Most of the time, parameter sniffing is either helping you, or is not hurting you. Sometimes, parameter sniffing turns bad and hurts you quite severely. Usually, but not always, this is because you either have severely skewed data (some data is very different than the rest, lots…
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05Dec 2016 by Grant Fritchey 3 Comments

Presentations for SQL Server Beginners

Azure, PASS, PowerShell, Professional Development, SQL Server, SQL Server 2016
[caption id="attachment_2548" align="alignleft" width="300"] Tired from all those blog posts[/caption] For my final blog post in the #gettingstarted, #iwanttohelp series, I decided to curate a set of presentations from the PASS Virtual Chapters. This content is available online. It's free. Most importantly for the person just getting started as a SQL Server data pro, it's good. I'm going to marry each of the presentations with my eleven blog posts in this series. The Importance of a Full Backup in SQL Server For this one I'm going to recommend Tim Radney's session Understanding SQL Server Backup and Restore. I know Tim personally and guarantee this is a good session. Why Is The Server Slow Jes Borland is a very close personal friend and an absolutely outstanding presenter (and person). She has…
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28Nov 2016 by Grant Fritchey 1 Comment

Database Clone

SQL Server 2016, T-SQL
There are a bunch of ways you could create a database clone. Backup and restore is one method. Export/Import is another. There are even third party tools that will help with that. However, each of these has a problem. It's moving all the data, not just once, but twice. You move the data when you export it and you move it again when import it (same thing with backup and restore). That makes these methods slow for larger databases. How can you create a database clone without moving the data multiple times? Don't Move the Data At All New with SQL Server 2016, expanded in SP1, and added to SQL Server 2014 SP2 is a new command, DBCC CLONEDATABASE. This is like a dream come true. The use is extremely…
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23Nov 2016 by Grant Fritchey 5 Comments

PowerShell to Test a Query

DevOps, PowerShell, SQL Server, SQL Server 2016, T-SQL
So you want to do some tuning, but you're not sure how to test a query on it's performance. Not a problem. Here's a very rough script that I use to do some recent testing. This script to test a query is post #11 of the #enterylevel #iwanttohelp effort started by Tim Ford (b|t). Read about it here. The Script The goal here is to load a bunch of parameter values from one table and then use those values to run a query to test it. To do this I connect up to my SQL Server instance, naturally. Then I retrieve the values I'm interested in. I set up the query I want to test. Finally a loop through the data set, calling the query once for each value. [reflection.assembly]::LoadWithPartialName("Microsoft.SqlServer.Smo") | out-null #…
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22Nov 2016 by Grant Fritchey 19 Comments

SQL Server on Linux: Boring

SQL Server 2016
As a concept, SQL Server on Linux is thrilling. Due to this, the OS doesn't stand in the way of taking advantage of everything that SQL Server offers. Because we have Linux, we have opportunity for all sorts of new fun. I first saw SQL Server running on Linux about six months ago. The install was shockingly easy. I saw a few command line commands run and it all looked good. I didn't have the opportunity to set up my own full blown install then, but I do now. My Installation Today I did all the work necessary to get this thing running. I got a copy of Ubuntu Desktop and put it on VMWare Workstation in a virtual machine. That was a painless process. SIDE NOTE: It was a painless process…
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07Nov 2016 by Grant Fritchey 2 Comments

sp_executesql Is Not Faster Than an Ad Hoc Query

SQL Server, SQL Server 2016, T-SQL
This requires an immediate caveat. You should absolutely be using sp_executesql over any type of non-parameterized execution of T-SQL. You must parameterize your T-SQL because the lack of parameters in building up and executing strings is a classic SQL Injection attack vector. Using straight ad hoc T-SQL is an extremely poor coding choice because of SQL Injection, not because there is something that makes one method faster than the other. Yet, I see in performance checklists that you should be using sp_executesql over straight ad hoc T-SQL because it will perform faster. That statement is incorrect. Some Discussion Let me reiterate the caveat before we continue. I 100% advocate for the use of sp_executesql. This function is preferred over ad hoc SQL because, used properly (and isn't that usually one of the main problems,…
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24Oct 2016 by Grant Fritchey 10 Comments

A Sub-Query Does Not Hurt Performance

SQL Server, SQL Server 2016, T-SQL
The things you read on the internet, for example, "don't use a sub-query because that hurts performance." Truly? Where do people get these things? Let's Test It I've written before about the concept of cargo cult data professionals. They see one issue, one time, and consequently extrapolate that to all issues, all the time. It's the best explanation I have for why someone would suggest that a sub-query is flat out wrong and will hurt performance. Let me put a caveat up front (which I will reiterate in the conclusion, just so we're clear), there's nothing magically good about sub-queries just like there is nothing magically evil about sub-queries. You can absolutely write a sub-query that performs horribly, does horrible things, runs badly, and therefore absolutely screws up your system. Just as…
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