Development

T-SQL

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

T-SQL

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

Development

I stay in the nicest hotels It sounds really simple: Capture a bunch of production queries Replay those same queries over in a load test environment So what’s the big deal? Why is it so hard to find good guidance on how to pull this off? How hard can it be? Problem 1: many queries…

The Pleasure Of Presenting With Joe Obbish

January 3, 2019

Execution Plans, GroupBy Conference, Indexing, Videos

Grouple On At the December 2018 GroupBy I had the honor of co-presenting with one of the smartest guys around, Joe Obbish. Here’s the video of our session, “The Problems With Optional Operators”, and a link to the resources. Enjoy! Resources: Slides and Demos

Why Do Some Indexes Create Faster Than Others?

January 3, 2019

To warn you ahead of time, this post is an exploration without an answer (yet). There’s some interesting stuff in here, but no conclusions. If that’s not your kind of post, feel free to skip it. If it is, well, here goes nothin’… Wild, Wild Life Creating indexes is kind of a funny thing. By…

When Does SARGability Matter Most?

December 27, 2018

!erehT iH I know what you’re thinking. Another post about how you should just never do this one thing and all your queries will magically end up faster. Just watch the video. For more reading, check out these posts: Sargability: Why %string% Is Slow Optional Parameters and Missing Index Requests Computed Columns: Reversing Data…

5 Ways to Change Execution Plans Without Tuning

December 21, 2018

A couple years back, I realized there were at least Ten Ways to Set MAXDOP. These days, as I write and tune queries, I realize there are an awful lot of ways to change the Cardinality Estimator (CE) and Query Optimizer, too. Let’s take a quick survey of five intriguing options. 1. Change your SQL…

Do Functions Stop You From Using Indexes?

December 20, 2018

Indexing, T-SQL

Say I’ve got a function in my WHERE clause: Transact-SQL SELECT DisplayName FROM dbo.Users WHERE LTRIM(RTRIM(DisplayName)) = 'Brent Ozar'; 123 SELECT DisplayName FROM dbo.Users WHERE LTRIM(RTRIM(DisplayName)) = 'Brent Ozar'; If I have an index on DisplayName, will SQL Server use it? Sure: Function in the WHERE clause Even though SQL Server can’t seek to “Brent Ozar,” it will…

Query Store And Cruel Defaults

December 19, 2018

Execution Plans, Query Store (QDS)

Gosh Darn Now, look, it’s no secret that I think Query Store is cool. Heck, I went and wrote sp_BlitzQueryStore so you can examine it similarly to how sp_BlitzCache looks at the plan cache. For a variety of reasons, though, we run into people who can’t or won’t turn it on, or who had to turn…

Comparison Review: Microsoft SSDT vs Redgate SQL Source Control

December 17, 2018

Alex Yates

Development

Hi. I’m still not Brent. My name’s Alex, and I care about databases, DevOps and data protection. Last year I delivered a session on GroupBy all about how to do Database DevOps right, and back in May I wrote a blog post for BOU about how to screw it up. Now, dear reader, I’m going…

Never Judge A Query By Its Cost

December 13, 2018

Signs and Numbers When tuning queries, or even finding queries to tune, there’s a rather misguided desire to look for queries with a high cost, or judge improvement by lowering query cost. The problem is that no matter what you’re looking at, costs are estimates, and often don’t reflect how long a query runs for…

“Surely this one will get a clustered index scan.”

December 7, 2018

I love building demos for our training classes because I’m constantly in a battle of the minds with SQL Server. I try to guess what he’s going to do next, and I love it when he surprises me. I started by building a new parameter sniffing demo with the Stack Overflow database, and in this…

Indexed View Matching With GROUP BY And DISTINCT

December 5, 2018

Bit Of A Kick I’ve been playing with indexed views a little bit lately for some demos in my Bits Precon. There are a whole bunch of limitations in creating indexed views. One of them is that you can’t base the query on DISTINCT. Fair enough, but you can do GROUP BY. And what’s pretty…

What Is SQL Injection?

December 1, 2018

T-SQL

Say we have a stored procedure that queries the Stack Overflow database. We have two separate parameters, @DisplayName and @Location, so folks can search for people by name, location, or both. For performance reasons, we decide to build dynamic SQL: Transact-SQL CREATE OR ALTER PROC dbo.UserSearch @DisplayName NVARCHAR(40) = NULL, @Location NVARCHAR(100) = NULL AS…

Tales From Overindexing: Too Many One Column Indexes

November 29, 2018

Execution Plans, Indexing, SQL Server

Master Plan Sometimes you see a query, and it’s hitting one table, and then the query plan looks like a vase full of spaghetti. Usually, there’s a view involved. Usually. Sometimes, there’s just really weird indexing. Here’s A Thing, Look At It Promises This is a query against one table. No views, no functions, no…

How to Troubleshoot Blocking and Deadlocking with Scripts and Tools

November 28, 2018

Deadlocks, Monitoring, sp_BlitzLock

When you need to find which queries are blocking other queries, your decision comes down to when the blocking happened. Is it happening now, recently, or coming up soon? During a live emergency, start with sp_WhoIsActive. Adam Machanic’s excellent free sp_WhoIsActive replaces Activity Monitor, sp_who, and sp_who2, and it’s way more powerful. The documentation is extensive –…

Getting Sneaky With Forced Parameterization

November 27, 2018

Silly Rules I’ve blogged about some of the silly rules about where Forced Parameterization doesn’t work. One rule that really irked me is this one: The TOP, TABLESAMPLE, HAVING, GROUP BY, ORDER BY, OUTPUT…INTO, or FOR XML clauses of a query. TOP and FOR XML, get used, like, everywhere. TOP is pretty obvious in its usage.…

Not So Forced Parameterization

November 26, 2018

Asking The Wrong Question Sometimes, when you wanna turn on a feature, you spend so much time wondering if you should, you don’t bother asking if it’ll even work when you do. There are a long list of things that are incompatible with Forced Parameterization, on a page that’s pretty hard to find. Now, there’s…

Adventures In Foreign Keys 5: How Join Elimination Makes Queries Faster

November 16, 2018