Indexing

You’re lazy and overconfident. You’ve been reading this blog for a while, and you’ve been telling yourself, “Yeah, I’m pretty good at this database thing. I’ve got years of experience under my belt. I know the fundamentals.” You’ve told yourself, “Yeah, someday I’ll get to Brent’s How to Think Like the Engine class,” but…you’ve never…

Free Columnstore Training Class on Tuesday

Last Updated April 1, 2021

Your report queries are too slow. You’ve tried throwing some hardware at it: your production SQL Server has 12 CPU cores or more, 128GB RAM, and SQL Server 2016 or newer. It’s still not enough to handle your growing data. It’s already up over 250GB, and they’re not letting you purge old data. Will columnstore…

Partitioned Tables Cause Longer Plan Compilation Times.

Last Updated February 26, 2021

Partitioning

Folks sometimes ask me, “When a table has more indexes, and SQL Server has more decisions to make, does that slow down execution plan generation?” Well, maybe, but the table design choice that really screws you on compilation time is partitioning. If you choose to partition your tables, even tiny simple queries can cause dramatically higher…

Free Webcast: Help! My SQL Server Maintenance is Taking Too Long!

Last Updated January 22, 2021

Backup and Recovery, Company News, Index Maintenance, Production Database Administration

“Time for a smoke break.” You manage growing SQL Server databases with shrinking nightly maintenance windows. You just don’t have enough time left each night to do the necessary backups, corruption checking, index maintenance, and data jobs that your users and apps want to run. Cloud storage isn’t helping the problem, either. Stop playing Tetris…

Autoparameterized Trivial Queries May Not Get Partition Elimination

Last Updated November 26, 2020

Partitioning

How’s that for a niche topic? You’re probably never going to know this, but since I had to figure it out the hard way, I’m writing this down so I don’t forget it: queries that get trivial optimization may not get partition elimination. This post is going to be a little on the long side…

When Do I Need to Use DESC in Indexes?

Last Updated November 30, 2020

If I take the Users table from any Stack Overflow database, put an index on Reputation, and write a query to find the top 100 users sorted by reputation, descending: CREATE INDEX Reputation ON dbo.Users (Reputation); SELECT TOP 100 * FROM dbo.Users ORDER BY Reputation DESC; 12345 CREATE INDEX Reputation ON dbo.Users (Reputation); SELECT TOP 100…

Want to use columnstore indexes? Take the ColumnScore test.

Last Updated September 27, 2020

When columnstore indexes first came out in SQL Server 2012, they didn’t get a lot of adoption. Adding a columnstore index made your entire table read-only. I often talk about how indexing is a tradeoff between fast reads and slow writes, but not a lot of folks can make their writes quite that slow. Thankfully, Microsoft…

Announcing a New Class: Fundamentals of Columnstore

Last Updated September 26, 2020

Your report queries are too slow. Will columnstore indexes help? You’ve tried throwing some hardware at it: your production SQL Server has 12 CPU cores or more, 128GB RAM, and SQL Server 2016 or newer. It’s still not enough to handle your growing data. It’s already up over 250GB, and they’re not letting you purge…

Unindexed Foreign Keys Can Make Performance Worse.

Last Updated December 29, 2021

Foreign Keys

I know. You, dear reader, saw that title and you came in here because you’re furious. You want foreign key relationships configured in all of your tables to prevent bad data from getting in. But you gotta make sure to index them, too. Let’s take the Stack Overflow database – I’m using the 50GB Stack…

Free Webcast Wednesday: Pushing the Envelope with Indexing for Edge Case Performance

Last Updated September 13, 2020

Most of the time, conventional clustered and non-clustered indexes work just fine – but not all the time. When you really need to push performance, hand-crafted special index types can give you an amazing boost. Join Microsoft Certified Master, Brent Ozar, to learn the right use cases for filtered indexes, indexed views, computed columns, table…

SQLBits Attendees: Here Are Your Prerequisites for Mastering Index Tuning.

Last Updated September 1, 2020

Howdy folks. It’s time for SQLBits! This year, I’m teaching a one-day Mastering Index Tuning workshop from 9AM-5PM London time, and you can join in online. Pricing is £300 for the one-day workshop, or £800 for a full conference pass. You can register here. Once you’re registered, here’s what you need to do: Watch my…

[Video] How to Think Like Clippy (Subtitle: Watch Brent Wear Another Costume)

Last Updated July 27, 2020

Indexing, Videos

Remember Clippy, the Microsoft Office assistant from the late 1990s? He would pop up at the slightest provocation and offer to help you do something – usually completely unrelated to the task you were trying to accomplish. Sadly, the Office team told Clippy that he didn’t make the stack rankings cut, so he relocated over…

When a Columnstore Index Makes Your Query Fail

Last Updated June 8, 2020

If you wanna count the number of rows in a table, I’ve usually said, “It doesn’t matter what you put inside the COUNT() – it can be COUNT(*), COUNT(Id), COUNT(1), or COUNT(‘Chocula’), or even COUNT(1/0) – it all works the same.” And that was true right up until I added a columnstore index. Start with…

SQL ConstantCare® Now Tells You Which Indexes to Drop.

Last Updated May 25, 2020

Indexing, SQL ConstantCare

Indexes slow down data changes. SQL Server doesn’t have the concept of asynchronous indexes – copies of the data that it could update later when it’s bored. It has to keep every nonclustered index up to date, every single time you change data, like a delete/update/insert. Mo’ indexes, mo’ problems. That’s why in my Mastering…

No, You Can’t Calculate the Tipping Point with Simple Percentages.

Last Updated May 7, 2020

This morning, Greg Gonzalez (who I respect) posted about visualizing the tipping point with Plan Explorer (a product I respect), and he wrote: The tipping point is the threshold at which a query plan will “tip” from seeking a non-covering nonclustered index to scanning the clustered index or heap. The basic formula is: A clustered…

If You Have Foreign Keys, Don’t Update Fields That Aren’t Changing.

Last Updated December 29, 2021

Foreign Keys, T-SQL

If you update a row without actually changing its contents, does it still hurt? Paul White wrote in detail about the impact of non-updating updates, proving that SQL Server works hard to avoid doing extra work where it can. That’s a great post, and you should read it. But foreign keys add another level of…

Why Ordering Isn’t Guaranteed Without an ORDER BY

Last Updated April 11, 2020

Indexing, T-SQL

If your query doesn’t have an ORDER BY clause, you can’t reliably predict the order of your results over time. Sure, it’s going to look predictable at first, but down the road, as things change – the indexes, the table, the server’s configuration, the size of your data – you can end up with some ugly…

[Video] What Percent Complete Is That Index Build?

Last Updated March 24, 2020

Index Maintenance, SQL Server 2017, Videos

SQL Server 2017 & newer have a new DMV, sys.index_resumable_operations, that show you the percent_completion for index creations and rebuilds. It works, but…only if the data isn’t changing. But of course your data is changing – that’s the whole point of doing these operations as resumable. If they weren’t changing, we could just let the operations…

Things to Consider When SQL Server Asks for an Index

Last Updated March 1, 2020