It's a somewhat late addition, but I have an all-day Training Day at SQLBits. It takes place on Thursday, February 28th. You can read all about it on the SQLBits web site. I want to take a moment here to expand on the information that we're going to cover. I think the abstract does a good job of conveying what we'll be doing all day, but I figured a little more detail won't hurt. Query Tuning is Hard This is the very first thing I talk about. Query tuning is hard. I've got a nearly 1,000 page book on the topic, which should give you an idea of just how much material there is to cover. With the training day I've decided to focus on the tools that Microsoft gives…
Gathering metrics is quite difficult if there are no queries. So, if you're working in non-production environments, but you still want to see some sort of load on the server, how can you do it? I use a simple PowerShell script to simulate load. Simulate Load I've posted a sample of the meat of the script before. It's a simple way to test a procedure. However, I've modified it to do a little more than just run the procedure forever. Here's the script: # connect to the database $SqlConnection = New-Object System.Data.SqlClient.SqlConnection $SqlConnection.ConnectionString = 'Server=WIN-8A2LQANSO51;Database=AdventureWorks2017;trusted_connection=true' # gather values $RefCmd = New-Object System.Data.SqlClient.SqlCommand $RefCmd.CommandText = "SELECT th.ReferenceOrderID, COUNT(th.ReferenceOrderID) AS RefCount FROM Production.TransactionHistory AS th GROUP BY th.ReferenceOrderID;" $RefCmd.Connection = $SqlConnection $SqlAdapter = New-Object System.Data.SqlClient.SqlDataAdapter $SqlAdapter.SelectCommand = $RefCmd $RefData = New-Object System.Data.DataSet…
The question that came up during a recent class I was teaching was: What if you have a plan guide to get the plan you want, but then decide, instead of using the plan guide, you'll just force the plan? Ummmm…. No idea. Let's test it. First, Create a Plan Guide I have a couple of queries I use to teach about how statistics affects plan choice, so we'll use that here. I'm going to also define and create a plan guide that makes this plan use a small row count for all queries against it: CREATE OR ALTER PROC dbo.AddressByCity @City NVARCHAR(30) AS SELECT a.AddressID, a.AddressLine1, a.AddressLine2, a.City, sp.Name AS StateProvinceName, a.PostalCode FROM Person.Address AS a JOIN Person.StateProvince AS sp ON a.StateProvinceID = sp.StateProvinceID WHERE a.City = @City; GO…
At a recent all-day seminar on query performance tuning I was asked a question that I didn't know the answer to: "How do join hints affect adaptive joins?" I don't know. Let's find out together. Adaptive Joins Here's a query that we can run against AdventureWorks: SELECT p.Name, COUNT(th.ProductID) AS CountProductID, SUM(th.Quantity) AS SumQuantity, AVG(th.ActualCost) AS AvgActualCost FROM Production.TransactionHistory AS th JOIN Production.Product AS p ON p.ProductID = th.ProductID GROUP BY th.ProductID, p.Name; Without a columnstore index in SQL Server 2017, the execution plan looks like this: Let's introduce a columnstore index: CREATE NONCLUSTERED COLUMNSTORE INDEX ix_csTest ON Production.TransactionHistory ( ProductID, Quantity, ActualCost ); Now, if we run the same query, the execution plan changes to use an adaptive join like this: You can read more on adaptive joins here…
Four years ago, after a bunch of dithering and some negotiations with Tony Davis, my editor, I started to update my book, SQL Server Execution Plans. We managed to convince Hugo Kornelis to be the tech editor. I started to do the real writing in early 2015. I was most of the way through a first draft and no one liked it. Tony was unhappy. Hugo was unhappy. I was unhappy. I was just trying to update the existing book, SQL Server Execution Plans. It wasn't working. We all came to the conclusion that the old book was wrong. Not simply in a technical sense, although there was a lot of that, but in a structural sense. So we started rearranging things. SQL Server 2014 came out, but I was…
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…
I've posted a number of new videos to the Youtube channel that might be of interest if you're a data professional. First up, I've started migrating my Database Fundamentals posts over to Youtube as SQL Server Fundamentals. The first one is available: [embedyt] https://www.youtube.com/watch?v=NHkzj9ZRhbk[/embedyt] Speaking of DBAs, the job is not going away, but it is changing. Find out how to survive the change: [embedyt] https://www.youtube.com/watch?v=loUwmKQ_Eg4[/embedyt] Would you like to know how the Query Store works? Here's a getting started video: [embedyt] https://www.youtube.com/watch?v=XK8rBO9R43c[/embedyt] I also have a good video on how to combine capturing query metrics along with wait statistics using Extended Events: [embedyt]https://www.youtube.com/watch?v=nYyTSxry03A&t=97s[/embedyt] Wait until you see what Trace Flag 7412 can do for you. It's very cool. [embedyt]https://www.youtube.com/watch?v=ei2zJwZyRic&t=79s[/embedyt] Finally, if you are interested in attending one of my…
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…
I'm desperately working to finish up a new version of my book on Execution Plans. We're close, so close. However, you do hit snags. Here's one. My editor decided to change one of my queries. I used a local variable so that I got one set of behaviors. He used a hard-coded value to get a different set. However, the really interesting thing was that his query, at least according to the execution plan, went to simple parameterization. Or did it? Simple Parameterization The core concept of simple parameterization is easy enough to understand. You have a trivial query using a hard-coded value like this: SELECT * FROM Person.Person AS p WHERE p.BusinessEntityID = 42; The resulting execution plan looks like this: The initial, graphical, pointer that we're seeing parameterization…
I've been in love with the concept of a database as a service ever since I first laid eyes on Azure SQL Database. It just makes sense to me. Take away the mechanics of server management and database management. Focus on the guts of your database. Backups, consistency checks, these easily automated aspects can just be taken care of. Same thing goes with some, not all, but some, index management. Azure SQL Database can manage your indexes for you. I call it weaponizing Query Store. Anyway, I needed a way to automate this for the book I'm writing. I couldn't find any good examples online, so I built my own. Queries in Need of Automatic Indexing Because I want this to be as simple and repeatable as possible, I'm using…