Development

Over and over again, I run into applications that don’t parameterize their queries, and as a result: Compilations/sec is nearly as high as Batch Requests/sec CPU is high due to all those compilations Plans rarely last for more than a few hours in the cache Monitoring tools that track resource-intensive queries are useless because every…

What’s Better, CTEs or Temp Tables?

Last Updated August 1, 2020

I get this question a lot, so let’s set up an example with the Stack Overflow database. My query’s goal is to: Find the top 5 Locations List the users who live in those top 5 Locations, alphabetized by their DisplayName There are a LOT of ways I could write this query, but for the…

Scalar function execution plans, SQL Server 2017

User-defined scalar functions suck – even when they don’t access data.

Last Updated May 27, 2019

The performance of scalar functions sucks hard. Let’s see it in action using the Stack Overflow database – any size will work. I’ll set things up first in case you want to follow along: Transact-SQL USE StackOverflow2013; GO ALTER DATABASE CURRENT SET COMPATIBILITY_LEVEL = 140; GO EXEC DropIndexes; GO EXEC sp_configure 'cost threshold', 5; EXEC…

9 Tips for Faster SQL Server Applications

Last Updated May 23, 2019

Wanna make your SQL Server applications go faster? Here are 9 simple tips that will give you a better chance for success. They’re not carved in stone, but they’re a good place to start. Query Design Tips 1. Code for readability first. The easier your query is for humans to understand, the more likely SQL…

Why Order Isn’t Guaranteed Without an ORDER BY

Last Updated May 15, 2019

Execution Plans

Start with the Stack Overflow database, with no nonclustered indexes. If you’ve been playing around with demos, run my DropIndexes proc just to clear things out, which leaves the clustered indexes in place. Say you run this query: Transact-SQL SELECT TOP 100 Id, DisplayName FROM dbo.Users; 12 SELECT TOP 100 Id, DisplayName FROM dbo.Users; By default,…

Which Queries Should You Cache in the Application?

Last Updated May 9, 2019

I’ve talked about how the fastest query is the one you never make, and why when you’re scaling up a database application, you probably want to start caching query results in the app tier. Caching means: Less licensing costs for SQL Server Lower CPU usage both for query execution and for compilation time Lower locking/blocking…

The Silent Bug I Find in Most Triggers

Last Updated May 6, 2019

Get Notebook – FAQ I don’t have a problem with triggers. They get the job done when you need to implement business logic in a hurry, and you’re not allowed to change the application. As long as you keep the number of statements to a minimum (say, 2-3), and don’t try to do something really…

SSMS v18 and Azure Data Studio: The Golden Age of SQL Server Tooling

Last Updated April 27, 2019

Azure Data Studio

Yesterday, SQL Server Management Studio 18.0 shipped. Here’s the official announcement, the download page, and the release notes. Yes, it’s still free, and yes, they’re still adding features. Yes, they removed database diagrams and the debugger. (Update Apr 27: if you want the debugger, use Visual Studio – download.) No, SSMS 18 doesn’t run on…

Free SQL Server Load Testing Tools

Last Updated April 22, 2019

Load Testing

So you wanna run a load test against SQL Server. One thing I need you to understand first: you have to provide the database and the queries. Almost all of the tools in this post, except the last one, are designed to help you run queries, but they don’t include the queries. The whole idea…

15 Reasons Your Query Was Fast Yesterday, But Slow Today

Last Updated May 26, 2020

Development, Parameter Sniffing

SQLSaturday Israel 2019 speaker shirt In rough order of how frequently I see ’em: There are different workloads running on the server (like a backup is running right now.) You have a different query plan due to parameter sniffing. The query changed, like someone did a deployment or added a field to the select list.…

Index scans aren’t always bad, and index seeks aren’t always great.

Last Updated April 16, 2019

Execution Plans, Indexing

Somewhere along the way in your career, you were told that: Index seeks are quick, lightweight operations Table scans are ugly, slow operations And ever since, you’ve kept an eye on your execution plans looking for those performance-intensive clustered index scans. When you see ’em, you go root ’em out, believing you’ve got a performance…

Finding Froid’s Limits: Testing Inlined User-Defined Functions

Last Updated June 25, 2020

Execution Plans, Parameter Sniffing, SQL Server 2019, T-SQL

This week, I’ve been writing about how SQL Server 2019’s bringing a few new features to mitigate parameter sniffing, but they’re more complex than they appear at first glance: adaptive memory grants, air_quote_actual plans, and adaptive joins. Today, let’s talk about another common cause of wildly varying durations for a single query: user-defined functions. Scalar…

1 query, 3 parameters, 3 different plans

Parameter Sniffing in SQL Server 2019: Adaptive Joins

Last Updated May 26, 2020

Adaptive Joins, Parameter Sniffing, SQL Server 2019

So far, I’ve talked about how adaptive memory grants both help and worsen parameter sniffing, and how the new air_quote_actual plans don’t accurately show what happened. But so far, I’ve been using a simple one-table query – let’s see what happens when I add a join and a supporting index: Transact-SQL CREATE INDEX IX_OwnerUserId_Includes ON…

Parameter Sniffing in SQL Server 2019: Air_Quote_Actual Plans

Last Updated May 26, 2020

Execution Plans, Memory Grants, Parameter Sniffing, SQL Server 2019

My last post talked about how parameter sniffing caused 3 problems for a query, and how SQL Server 2019 fixes one of them – kinda – with adaptive memory grants. However, the post finished up by talking about how much harder performance troubleshooting will be on 2019 because your query’s memory grant is based on…

Parameter Sniffing in SQL Server 2019: Adaptive Memory Grants

Last Updated May 26, 2020

Memory Grants, Parameter Sniffing, SQL Server 2019

This week, I’m demoing SQL Server 2019 features that I’m really excited about, and they all center around a theme we all know and love: parameter sniffing. If you haven’t seen me talk about parameter sniffing before, you’ll probably wanna start with this session from SQLDay in Poland. This week, I’m going to be using…

Should we use stored procedures or queries built in the app?

Last Updated March 27, 2019

A client asked a great architecture question that deserved its own blog post: Should we use more “stored procedures” for select, insert, update, delete or should that just be sent as queries from the application? If you ask a junior database administrator where to put something, she’ll probably say “in the database” because that’s the…

How to fix the error “String or binary data would be truncated”

Last Updated January 18, 2020

To fix this error, patch to SQL Server 2016 SP2, CU6 or newer (including SQL Server 2017), and then turn on trace flag 460. You can enable it at the query level or at the server level. First, let’s see the error happen: let’s create a table with small fields, and then try to insert…

You know what your deadlock graphs need? Animation.

Last Updated February 21, 2019

Deadlocks

In SQL Server Management Studio, plain ol’ deadlock graphs look like this: Two thumbs down, would not lock the dead again BOOOOO-RING. That’s why I prefer opening deadlock graphs in SentryOne Plan Explorer, which presents a much better visual in the form of a circle…a circle, let’s just stop there: Deadlock graph in SentryOne Plan…

[Video] An Introduction to GitHub for DBAs

Last Updated February 8, 2019