10Sep 2018 by Grant Fritchey 1 Comment

Estimated Plans and Forced Plans from Query Store

SQL Server 2016, SQL Server 2017, T-SQL
While all plans are estimated plans, there is still a difference between capturing an estimated plan and looking at a plan from the cache or from query store. Or is there? A question came up during a recent presentation; what happens to capturing an estimated plan when you're forcing plans? Let's find out. The answer is interesting. Estimated Plans Here's my stored procedure that I'll be using with AdventureWorks2017: CREATE OR ALTER PROC dbo.ProductTransactionHistoryByReference (@ReferenceOrderID INT) AS BEGIN SELECT p.Name, p.ProductNumber, th.ReferenceOrderID FROM Production.Product AS p JOIN Production.TransactionHistory AS th ON th.ProductID = p.ProductID WHERE th.ReferenceOrderID = @ReferenceOrderID; END; For reasons I'll explain in a bit, I'm going to free the procedure cache: ALTER DATABASE SCOPED CONFIGURATION CLEAR PROCEDURE_CACHE; Then, if I capture an estimated plan for two different values:…
Read More
27Aug 2018 by Grant Fritchey 4 Comments

Why I Love Extended Events, Reason 394: Customize Live Data

Azure, SQL Server, SQL Server 2016, SQL Server 2017
There are so many reasons to love Extended Events that it can really be overwhelming, but, one more reason that I love them are the ability to customize Live Data. More importantly, you can share that customization with others or move it between machines. Let's explore this. Customize Live Data If you open up an Extended Events file, or connect to a running Session, you're looking at the Live Data window and it looks something like this: I won't lie, that's a pretty ugly UI. At the top are all the events you've captured. At the bottom are the event fields. If you want to look at the information in different events, you click on the event, then down at the fields... blech! However, I have some options. Let's right…
Read More
20Aug 2018 by Grant Fritchey 1 Comment

Actual Execution Plan Costs

T-SQL
Why don't "actual execution plans" have "actual execution plan costs"? This is a question and a myth I have to fight against all the time. It's so hard to convince people that all execution plans are estimated plans in the first place (by the way, all execution plans are estimated plans). If we execute a query at the same time we capture a plan, we have enabled SQL Server to also capture run-time metrics with that plan. So we end up with what is known as an actual plan, but it's still just an estimated plan plus those run-time metrics. Execution Plan Costs When you look at a given operator within an estimated plan, it's going to show you four numbers related to cost: Estimated CPU Cost Estimated I/O Cost…
Read More
13Aug 2018 by Grant Fritchey 3 Comments

Measuring Query Execution Time: What Is Most Accurate

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL, Tools
Probably the single most important factor when deciding which query to tune, or actively tuning a query, is how you go about measuring query execution time. SQL Server provides a number of different mechanisms (really, maybe too many) to get this done. However, all measures are not created equally. In fact, they frequently disagree with one another. Let's take a look at this odd phenomenon. Measuring Query Execution Time Before we get into all the choices and compare them, let's baseline on methodology and a query to use. Not sure why, but many people give me blow back when I say "on average, this query runs in X amount of time." The feedback goes "You can't say that. What if it was just blocking or resources or..." I get it.…
Read More
06Aug 2018 by Grant Fritchey 2 Comments

Analyze Actual Execution Plan

SQL Server
One of the many new sets of functionality introduced in SQL Server Management Studio 17 is the new option "Analyze Actual Execution Plan." If Microsoft continues down this path, there will be a lot of useful functionality at some point. If you haven't yet looked at Analyze Actual Execution Plan, well, read on. Analyze Actual Execution Plan To get to the new functionality, you have to have an Actual Execution Plan open within SSMS 17. After that, it's just a matter of right clicking to bring up the context menu: If you select the menu choice, then a new window opens at the bottom of the execution plan, showing each of the batch statements in one tab, and some interesting stuff in the next tab: You can click that to…
Read More
23Jul 2018 by Grant Fritchey 5 Comments

Database Fundamentals #18: The SELECT Statement

Database Fundamentals
In my previous Database Fundamentals post, I showed you how to use the Query Designer to build a query. That was a SELECT statement. The basic construct of all your SELECT statements will be the same. You’re going to define a list of columns, the table or tables you’re interested in, and some sort of filter criteria. That’s the bare bones basics of how it works. But, as we all know, the devil is in the details. There are lots and lots of details. This section will introduce the T-SQL SELECT statement and start explaining some of those details. Column List You’ve been introduced to the basic concepts of the column list in the SELECT statement. It represents the information that is going to be available for display by whatever…
Read More
05Jul 2018 by Grant Fritchey 60 Comments

Why Aren’t You Using SSMS 17?

SQL Server, SQL Server 2016, SQL Server 2017
Last fall, Microsoft split the coding and release of SQL Server Management Studio away from any dependency on the server code. With that, they began an aggressive and exciting series of releases with exciting new functionality in each release. However, you don't care. How do I know? I've seen the telemetry that shows that most of you are still using old versions of SSMS. I want to know why. Please, post comments below so I can understand. Why You Should Move to SSMS 17 There are a ton of reasons for you to make the move. The least of which is bug fixes are coming hot and fast. The more exciting things are the ability to compare execution plans or the new Extended Events sessions that look just like those…
Read More
18Jun 2018 by Grant Fritchey 11 Comments

Database Fundamentals #17: Learning T-SQL

Database Fundamentals
While SQL Server Management Studio (SSMS) provides a robust graphical user interface (GUI), the commands you're going to use the most to control databases and the data within them in SQL Server are going to be done through T-SQL. Therefore, you really need to spend time learning how to write, read, and edit T-SQL. Previous posts in the Fundamentals series have showed how to INSERT, UPDATE and DELETE data using T-SQL. Next, we're going to learn SELECT. However, I want to show you a crutch you can use as you get started learning how to write T-SQL, the Query Designer window. The instruction on this topic is only meant to provide a mechanism to focus on the more important topic, learning T-SQL. However, this may be an easier path for…
Read More
11Jun 2018 by Grant Fritchey 6 Comments

Plan Metrics Without the Plan: Trace Flag 7412

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I place a lot of emphasis on capturing actual execution plans because of the runtime metrics, but with Trace Flag 7412, we don't need the plan. This is great news, because capturing execution plans, even using extended events, is an expensive proposition. However, using either the query_thread_profile event, or, Trace Flag 7412, we can get the runtime metrics without the plan. Trace Flag 7412 Here's how it works.You can either be running the extended event, query_thread_profile (a debug event, but one documented and supported by Microsoft) or, enable the Trace Flag 7412. I like to use the extended event in a targeted fashion to easily see behaviors on a query without having to capture the plan. You can even capture the information and then combine it with an estimated plan…
Read More
04Jun 2018 by Grant Fritchey 5 Comments

Extended Events, the system_health Session, and Waits

SQL Server, SQL Server 2016, SQL Server 2017, T-SQL
I advocate for, use, document, teach, and just downright love, Extended Events. They are so much better than the old Trace Events (aka, Profiler) that it's sometimes difficult to keep from just gushing. Let's talk about a common situation that you're going to run into on your servers all the time and how you can put Extended Events to work to help you, without actually doing any work at all. What's that? Be lazy and get rewards? Yes. The Extended Events system_health Session On your servers, any of them that are SQL Server 2008 or newer, right now, unless you've performed actions to prevent this, you're running the Extended Events system_health session. It's just happening, currently, on all your servers. Nothing you need to do about it at all. I'll…
Read More