Why Is The Server Slow?

SQL Server, SQL Server 2016, T-SQL
This is blog post #2 in support of Tim Ford's (b|t) #iwanttohelp, #entrylevel. If you haven't been working in SQL Server for very long, you may not have got this phone call yet, but you will: Hi, yeah, the server is slow. Thanks. Bye. Let's pretend for a moment that you know which server they're referring to (because just finding out that piece of information can be a challenge). Now what? The list of tools and mechanisms within SQL Server for gathering metrics is extremely long: Performance Monitor Dynamic Management Views & Functions System Views Extended Events Trace Events Activity Monitor Data Collector Execution Plans 3rd Party Tools I'm leaving out lots of stuff in that list. So where do you start when you get this phone call? Where is the server slow?…
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Finding Your Query in Query Store

Azure, SQL Server 2016, T-SQL
Query Store is pretty amazing. I'm loving working with it. I think it's likely to change how query tuning will be done in the future. Lots of people are probably going to just use the reports and tools in SQL Server Management Studio. However, a pretty healthy chunk of us will start using the system views in order to programmatically access the information stored in Query Store. One of the first things you're going to want to do is track down your query. The primary views you'll want are sys.query_store_query and sys.query_store_query_text. They join together based on the query_text_id. Let's take four scenarios and see if we can retrieve the correct query. First up, an ad hoc query: SELECT e.NationalIDNumber, p.LastName, p.FirstName, a.City, bea.AddressTypeID FROM HumanResources.Employee AS e JOIN Person.BusinessEntityAddress AS…
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“Applies To…” in the MSDN Documentation

Azure, SQL Server 2016, T-SQL
Quick little post. I just wanted to share how happy I am with the new "THIS TOPIC APPLIES TO" infographic. An example here: I think it makes things much more clear when you're attempting to figure out what's up with some T-SQL syntax. Well done Microsoft and thank you. Side note, this only exists in documentation that has been updated recently. I first saw it in some documentation that was updated January 11, 2016. It's not there in another piece of documentation I saw that was updated October 15, 2015. Here's hoping it gets put everywhere. It works.
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Statistics for the New Data Pro

PASS, SQL Server, SQL Server 2016, T-SQL
Next week at the PASS Summit I'll be presenting a session called Statistics for the New Data Pro. You can read the abstract at the link. I just want to emphasize that this is a beginner level session. I think way too many people who are just starting out with SQL Server don't understand the role that statistics play in determining how your queries are going to behave. What's more, too many people don't know how to get and read statistics to understand how it is that the optimizer thinks you have X number of rows in your database that match a given value. I'm going to make darned sure that the people who attend this session come out with a full understanding of how to read the statistics. This includes…
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Trace Flags in Azure SQL Database

Azure, SQL Server 2016, T-SQL
One of the ways that you take more direct control over your SQL Server instances is through the use of trace flags. There are a number that people recommend you enable by default. Prior to Extended Events for example, I'd say you should turn on trace flag 1222 in order to capture deadlock information on your server (now I just recommend you use the system_health session). I absolutely think you should turn on trace flag 2371 to get better behavior out of your automated statistics updates. There are others that I'll leave to all the systems experts to advise you on. What about Azure SQL Database? I doubt you'll be shocked, but if I try this: DBCC TRACEON (2371,-1); I get the following error: Msg 2571, Level 14, State 3,…
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Targeted Plan Cache Removal

Azure, T-SQL
A lot of times you'll hear how people are experiencing sudden, intermittent, poor performance on a query, bad parameter sniffing at work, so they'll fix it by running the following code: DBCC FREEPROCCACHE(); BOOM! Yeah, you just nuked the cache on your server because you wanted to take out a single terrorist query. Now, yes, that problematic query is going to recompile and hopefully have a better execution plan. Also, so are all the other queries on your system. That spike in CPU and the slow-down all your business people are experiencing... Your fault for going nuclear. Instead of a nuke, why not use a sniper rifle to just remove the one problematic plan. Here's a little piece of code to help out: DECLARE @PlanHandle VARBINARY(64); SELECT @PlanHandle = deps.plan_handle FROM…
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Generating Estimated Plan and the Plan Cache

SQL Server, T-SQL
Does generating an Estimated Plan cause that plan to be loaded into the plan cache? No.   What? Still here? You want more? Proof? Fine. Let's first run this bit of code (but please, not on your production server): DBCC FREEPROCCACHE(); That will remove all plans from cache. Now, let's take this query and generate an Estimated Plan (CTL-L from your keyboard or by clicking on the "Display Estimated Execution Plan" button on the toolbar): SELECT * FROM Production.ProductModel AS pm; This will generate a trivial plan showing a scan against the Production.ProductModel table. Now, let's run another query: SELECT deqs.plan_handle FROM sys.dm_exec_query_stats AS deqs CROSS APPLY sys.dm_exec_sql_text(deqs.sql_handle) AS dest WHERE dest.text = 'SELECT * FROM Production.ProductModel AS pm;'; That's just an easy way to see if a plan_handle exists.…
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Differences Between Actual & Estimated Plans

SQL Server, T-SQL
I have, in the past, made way too much of the need for Actual Plans when doing performance troubleshooting. The primary reason for this is to get the Actual Plan in order to see the differences between the Actual and Estimated Row Counts as a means of understanding how the optimizer saw the data. But, is that the only thing that's different between Actual & Estimated Plans? Well, pretty much, yeah. I took two fairly average execution plans from SQL Server 2014 and ran them through Altova's XML Spy, which does XML comparisons similar to how Redgate SQL Compare will compare two data structures for you. Here is every single difference I found. Everything was additional information in the Actual Plan. In the information for the first operator, in my case,…
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Hey Kids! Let’s Put on a Show at the Old Barn

Azure, Database Lifecycle Management, DevOps, PASS, SQL Server, T-SQL
Alternate Title: I'm traveling a bunch. Let's get together and talk. A bunch of trips and presentations coming up, so I thought I'd share. First, I'll be SQL Saturday Omaha for my first time ever presenting in Nebraska. I'm excited to add this state to my list (which is almost over 40 now). If you're not doing anything August 15th, let's have a chat. Next, fingers crossed, I'll get selected to fly back to my home state, Oklahoma, to go to SQL Saturday OKC. These guys put on a great event and hey, it's Oklahoma so how can it be bad. I hope they announce soon. I need to schedule my flights. This one is on August 29th. September also has several events. First, I'll be at SQL Saturday Las…
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But I Don’t Have a Test Server…

Database Lifecycle Management, DevOps, SQL Server, T-SQL
I frequently see statements on forums along the lines of "I don't have a test server, so I'm going to do something I've never done before directly on my production servers..." This is usually followed by questions along the lines of: But that's OK and I won't get fired, right? So how do I know if it worked? Is that dangerous? The replies are: No. You should be fired You won't By All the Gods! Yes! It's stupidly, insanely, I don't really like my production server, my data, my boss, or my job, dangerous. Yes. I understand. You're working for a not-for-profit, so you can't afford tons of new servers. You're looking at a 50tb production server of which, you can't make a copy. Your bosses just don't want to spend the…
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