I love presenting sessions because you get so many interesting questions. For example, what happens with Optimize for Ad Hoc when Query Store is enabled? Great question. I didn't have the answer, so, on to testing. For those who don't know, Optimize for Ad Hoc is a mechanism for dealing with lots and lots of ad hoc queries. When this is enabled, instead of storing an execution plan the first time a query is called, a plan stub, basically the identifying mechanisms, for the plan is stored in cache. This reduces the amount of space wasted in your cache. The second time the query is called, the plan is then stored in cache. I'm going to set up Optimize for Ad Hoc and Query Store and, to clean the slate,…
One of the many advantages of SQL Cruise is the ability to have enough time during a presentation to be able to answer questions from the people there in great detail. One question came up while I was showing the new functionality of Query Store (available soon in SQL Server 2016, available right now in Azure SQL Database). What happens to plan forcing when you have OPTION RECOMPILE on a query? Great question. I have a favorite procedure I use to illustrate the functionality of parameter sniffing: 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; If this procedure is called with the value of 'Mentor' you get…
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…
While setting up example code for my presentation at SQL Cruise (which is going to be a fantastic event), I realized I wanted to purge all the data from my Query Store, just for testing. I did a series of searches to try to track down the information and it just wasn't there. So, I did what anyone who can phrase a question in less than 140 characters should do, I posted a question to Twitter using the #sqlhelp hash tag. Jamey Johnston (t|b) came through... and it was right there in the documentation that I had been reading, over and over. In fact, it was in the documentation in two different places. Reading is clearly a problem for me today. Just so that you know, it's actually really easy:…
The data in the Query Data Store is what makes all the magic happen. From collecting the aggregate performance metrics of a query to the various plans in use by that query to being able to force a plan, it's all controlled by the data within the Query Data Store system tables. The Question When I was presenting on this topic at the PASS Summit a few weeks ago, one great question came up (great question = answer is "I don't know"), well, I defaulted to an "I don't know" answer, but my guess was, "No." The question was: can you take a plan from one server, let's say a test server, export it in some way, and then import it to production? In this manner, you ensure that a…
The all new, in-person, PASS Data Community Summit is in just a few weeks. Since I'm shortly going to be publishing a 100% rewritten book on query tuning, I decided to take a look at what kind of sessions on the topic are going to be available at the Summit. Query Tuning With The Best You can search through the published sessions here. I didn't even bother typing in "query tuning". Far too lazy. I just typed "query" and already saw some amazing stuff. In no particular order... One of the people I've ALWAYS learned from, Kimberly Trip is delivering a precon, Indexing for Performance. That's going to be a great day of good learning. Kim is insanely knowledgeable and a fantastic presenter. Well worth your time. Erin Stellato, another…
A question that came up recently was how to track the query compile time. It's actually a pretty interesting question because, there aren't that many ways to tell how long it took to compile the query, and they don't necessarily agree. For most of us, most of the time, compile time for a given query doesn't matter. However, I love telling the story of the query I had on an old system that could run in 90ms, but took 5 minutes to compile. In short, sometimes compile time matters. How To See Query Compile Time If you want to see how long it takes a query to compile, you have, to my knowledge, three options. The first, and possibly easiest, is to look at the plan properties on an execution…
A lot of stored procedures have multiple statements and determining the most costly statement in a given proc is a very common task. After all, you want to focus your time and efforts on fixing the things that cause you the most pain. You simply don't have the time to tune every single statement in every single procedure. So, identifying the most costly statement is vital. Happily, Extended Events are here to help. Finding a Costly Statement Query tuning is initially an act of discovery. Which queries, batches, procedures are inflicting the most pain on us. That pain could be measured a bunch of ways. The three most common, in particular order, are: Frequency with with a given query/batch/procedure is called.Resources used by that query.Length of time that it takes…
Wouldn't it be great to just quickly and easily take a look at your system to see if you had any queries that ran for a long time, but, without actually doing any work to capture query metrics? Oh, yeah, I can do that right now, and so can you. All we need is something that is built into every single server you currently have under management (sorry, not Azure SQL Database) that is SQL Server 2008 or better: system_health system_health Extended Event Session The system_health Extended Events session is very well documented by Microsoft here. I've talked about it before, in relation to Azure SQL Database, and, on the same topic we're going over today, long running queries and waits (cause if you have a long running query, you…
Query tuning is not easy. In fact, for a lot of people, you shouldn't even try. It's much easier to buy more, bigger, better hardware. Yeah, the query is still slow on newer, faster hardware, but not as a slow as it was. However, sooner or later, you're going to have to start to spend time fixing queries. In fact, you can find that fixing queries actually is more cost effective than buying more hardware. The problem is, query tuning is not easy. So, what do you do? Microsoft Can Help There are a number of tools available to you, right now, provided by Microsoft that can help you better and more easily tune your queries. This ranges from extended events to query store, and absolutely includes execution plans and…