Development

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?

May 14, 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

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

April 25, 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

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

April 18, 2019

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.

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

April 11, 2019

Execution Plans, 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

April 10, 2019

Adaptive Joins, 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

April 9, 2019

Execution Plans, Memory Grants, SQL Server 2019

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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

April 8, 2019

Memory Grants, 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?

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”

March 20, 2019

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.

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

February 8, 2019

Development, Videos

Distributed source control is really intimidating: branches, pull requests, merges – will somebody just take my code, for crying out loud? Why does it have to be so complicated and involved? I’m with you: I hated GitHub. For years, I struggled with it, but I’ve come to a gradual truce. I’m not a GitHub pro…

Watch Brent Tune Queries: Fixing Nested Functions

January 24, 2019

When I do performance tuning for clients, I really pride myself on making as few changes as possible in order to make a tremendous difference. I consider it a failure when I have to tell someone to rewrite a bunch of queries from scratch. However, there are some cases where I just can’t work around…

Tuning Dynamic SQL by Hand with Short Circuits

January 23, 2019

When we think about building dynamic SQL, we usually think about a stored procedure like this that takes input parameters, builds a string, and then executes that string. Here’s a simple example: Transact-SQL CREATE OR ALTER PROC dbo.usp_SearchUsers @SearchDisplayName NVARCHAR(40) = NULL, @SearchLocation NVARCHAR(100) = NULL, @SearchReputation INT = NULL AS BEGIN DECLARE @StringToExecute NVARCHAR(4000);…

How to Load Test a Database Application

January 15, 2019