Development

DBA Training Plan, Locking, Blocking, and Isolation Levels

Locking isn’t a problem – queries are gonna lock data. As long as nobody else wants the lock, you can take your sweet time locking it, and it won’t show up as a problem. (That’s one of the many reasons queries work so well in development, and then hit performance issues in production.) Blocking, now…

DBA Training Plan 13: Why Do Cached Plans Go Bad?

August 26, 2019

DBA Training Plan, Execution Plans

It’s a little bit of a trick question: what could make a good query plan turn bad? In the last episode, we used sp_BlitzCache to spot the most resource-intensive, longest-running query plans in your server’s cache. Go run those queries again, right now, and I bet you’re going to see plans in the cache that…

Research Paper Week: Plan Stitch: Harnessing the Best of Many Plans

August 19, 2019

Those of you who follow me on Instagram, Twitter, or Facebook know I’m taking most of August off for vacation. Erika and I spent the last couple of weeks in Telluride, had a brief stop in Sacramento for SQL Saturday, and this week we’re touring wineries in Napa and Sonoma. As part of recharging, I…

DBA Training Plan 12: What Query Plans Are In Cache?

August 15, 2019

DBA Training Plan, Execution Plans, sp_BlitzCache

In the last episode, while talking about the basics of executing queries, I said that SQL Server caches execution plans in memory, reusing them whenever the same query gets executed again. I’ve also talked about the dynamic management views (DMVs) that let you query what’s in SQL Server’s memory. Let’s put those two things together…

DBA Training Plan 11: The Basics of Executing a Query

August 14, 2019

DBA Training Plan, Execution Plans

Up til now in the DBA Training Plan, we’ve been taking inventory of our servers, making sure the data’s well-protected, and understanding the basics of how the data’s stored in indexes inside those data files. Now, let’s start looking at performance, and let’s start by zooming really far out to think about how SQL Server…

“But NOLOCK Is Okay When The Data Isn’t Changing, Right?”

August 5, 2019

I’ve already covered how NOLOCK gives you random results when you’re querying data that’s changing, and that’s a really powerful demo to show folks who think NOLOCK is safe to use in production. However, I’ve gotten a question from several users: But I’m querying data that isn’t changing – sure, OTHER rows in the table…

Using Implicit Transactions? You Really Need RCSI.

July 9, 2019

Locking, Blocking, and Isolation Levels, Videos

Implicit transactions are a hell of a bad idea in SQL Server: they require you to micromanage your transactions, staying on top of every single thing in code. If you miss just one little DELETE/UPDATE/INSERT operation and don’t commit it quickly enough, you can have a blocking firestorm. The ideal answer is to stop using…

Poll Results: Yep, Developers are Using Unmasked Production Data.

July 5, 2019

Earlier this week, I asked where your developers are getting their development databases from. The poll results are in: 9% of development happens on the production database server 57% are copying the production data to another server, and using it as-is 31% are copying the production data, but then masking/scrambling private data before developers get…

What the Arrow Sizes in Query Plans Really Mean

June 21, 2019

Precisely 80.3% of you are going to learn something in this post. Earlier this week, I asked what you thought the arrows in estimated and actual query plans meant. I asked you to just guess without doing any research, and here’s what you answered: There are a lot of different opinions, and I can see…

Poll: What Do You Think The Arrow Sizes in Query Plans Mean?

June 18, 2019

Don’t read the documentation – just guess. What do you think the arrow sizes in query plans mean in SSMS 17/18? After you take the poll – just guess – then you can see what other people think. Friday, I’ll share a demo you can use to prove the answer.

Forced Parameterization Doesn’t Work on Partially Parameterized Queries.

June 12, 2019

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?

June 6, 2019

T-SQL

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.

May 28, 2019

T-SQL

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

May 21, 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

May 15, 2019

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

T-SQL

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