Beavis v. Butthead I was a bit surprised that this was a possibility with ColumnStore indexes, since “keys” aren’t really their strong point, but since we’re now able to have both clustered ColumnStore indexes alongside row store nonclustered indexes AND nonclustered ColumnStore indexes on tables with row store clustered indexes, this kind of stuff should…
That’s when it all gets blown away At one point or another in everyone’s SQL-querying career, they end up writing a query that goes something like this: SELECT something FROM stuff WHERE (@thing1 is NULL or whatever = @thing1) AND … These are often called optional parameters, and if you spend any time looking at…
Life Is Messy Demo queries have this nasty habit of being clean. Even using a pit of despair like Adventure Works or World Wide Importers, it’s easy to craft demo queries that fit the scenario you need to make yourself look like a genius. Stack Overflow, in all its simplicity, makes this even easier (lucky…
What happened in Part 1? Join Elimination, naturally. Until the end. My copy of the Stack Overflow database doesn’t have a single foreign key in it, anywhere. If we go down the rabbit hole a couple steps, we end up at a very quotable place, with Rob Farley. 2. Duplicated rows Not necessarily duplicated completely,…
My public SQL Server database copy of the Stack Overflow data dump only includes clustered indexes by default. I want to keep your database size as small as possible for quick downloading. But like any database – when you create it, should you add your own indexes to make queries go faster? The answer lies…
It’s one of those fierce religious wars that divides families and tears loved ones apart. First, if two tables are related, should we tell SQL Server about it? If SQL Server knows that there’s a relationship, then it can make better decisions when building execution plans. The problem is that SQL Server has to be…
Yazoo Over on his blog, fellow Query Plan aficionado Joe Obbish has a Great Post, Brent® about query patterns that qualify for Rowgroup Elimination. This is really important to performance! It allows scans to skip over stuff it doesn’t need, like skipping over the dialog in, uh… movies with really good fight scenes. Car chases?…
Sometimes I need to reset stuff during performance training classes. I know some of you teach classes, too, and some of you just like doing crazy stuff. So here you go, a stored procedure to lose weight fast: CREATE PROCEDURE [dbo].[DropIndexes] AS SET NOCOUNT ON CREATE TABLE #commands (ID INT IDENTITY(1,1) PRIMARY KEY CLUSTERED, Command…
There’s no Top in the title And that’s because a TOP without an ORDER BY is non-deterministic, and you’ll get yelled at on the internet for doing that. This is just a short collection of things that I’ve done in the past, and still find people doing today when troubleshooting performance. Sure, this list could…
Demo Day We use StackOverflow for demos a lot. For all the reasons Brent mentions in his Great Post, Brent©, it’s pretty awesome. Where things get tricky is with locking demos. Sometimes the modifications can take a long time. This may be by design if you need to show long-held locks by sessions that aren’t…
Using the good ol’ Stack Overflow public database, get the execution plan for this query – either estimated or actual, doesn’t matter: SELECT Id FROM dbo.Users WHERE LastAccessDate = ‘2016/11/10’; In the execution plan, SQL Server asks for a missing index on the LastAccessDate field: If you right-click on the plan and click Show Execution…
Alone Together When I think about SQL Server features, I often picture a high school cafeteria. AGs are making fun of Mirroring, index rebuilds are walking around taking everyone’s lunch, dta is making a glue sandwich, and no one knows who Service Broker is even though they’ve been going to school together since Kindergarten. At…
Mindless Self Promotion I liked writing this blog post so much that I wrote an entire presentation on it. If you’d like to see it at GroupBy, click the link and vote. Much has been written about this It’s probably one of the lowest hanging items a performance tuner can deal with. Don’t need all…
Facemaking You know when you think you know something, and the obviousness of it makes you all the more confident that you know it? That’s usually the first sign that there’s a giant gotcha waiting for you. And that’s what happened to me over the weekend. The setup I answered a question. And after I…
I often get the question of “Will SQL Server do an index seek with ____?” Another way to phrase it is, “Is this query sargable?” We throw the term “sargable” around to mean that SQL Server can do an index seek to satisfy your search arguments. (We’re specifically talking about index seeks here, not scans – not…
Disclaimer I found this totally by accident, and it even surprised me. You can probably guess the TL;DR on this is yes, huh? Dude, where’s my table variable? I was trying to come up with a demo for something totally different. Don’t ask. Seriously. It’s top secret. Okay, so it’s just embarrassing. Anyway. I had…
In my performance training class, people get really excited when I cover filtered indexes, computed columns, and indexed views. Then they get a really strange expression on their face when I talk about one of the biggest drawbacks: if your connection options aren’t set correctly, your delete/update/insert (DUI) operations will fail. That gave me a really…
Love/Hate When indexed views help, they make aggregation queries super fast. There are some kind of horrible limitations and requirements. When they hurt, your modifications slow to a crawl because SQL has to not only keep your horrible indexes synchronized, it also has to keep your indexed view indexes in sync now, too. But SQL…
When you’re tuning queries It’s sort of a relief when the first time you get your hands on it, you get the plan and there’s a missing index request. Even if it’s not a super high-value one, something in there is crying for help. Where there’s smoke, there’s a bingo parlor. But does adding missing…
Kid Tested When you work with something a lot, you tend to extrapolate concepts from it out to everything you see. That one person collecting tickets is a serial zone. That food truck line is a HEAP. The empty subway car that smells like a toilet is Replication. Stuff like that. If you have one…
