22Mar 2021 by Grant Fritchey 9 Comments

Query Store as an Upgrade Tool

SQL Server, Tools
There are a lot of uses for Query Store, but one of the most interesting is as an upgrade tool. We all know that upgrades in SQL Server can be more than a little bit nerve wracking. No matter how much you tested stuff in lower environments, deploying an update to production might result in performance issues as your code hits a regression. This is even more true when upgrading from versions of SQL Server prior to 2014 to anything 2014 and above. That's because of the new cardinality estimation engine introduced in 2014. Most queries won't notice it. Some queries will benefit from the better estimates. A few, problematic, queries will suffer. This is where Query Store can be used as an upgrade tool. The Steps We're going to…
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18May 2020 by Grant Fritchey 2 Comments

Can We Get Row Counts After Execution?

SQL Server, T-SQL
The general idea for this question came from dba.stackexchange.com: could we, and if we can, how, get row counts after execution. I was intrigued with the idea, so I ran some tests and did a little digging. I boiled it all down in the answer at the link, but I figured I could share a little here as well. Properly Retrieve Row Counts After Execution The right way to do this is obvious and simple. Before you need it, set up an Extended Events session. Done. The only question is what goes into the Session. First blush, sql_batch_completed and/or rpc_completed. Both will return a rows affected value. Although, interestingly, the row_count value is documented as rows returned. However, it's both. But, if you really want to get picky, batches and…
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11May 2020 by Grant Fritchey 7 Comments

Find Indexes Used In Query Store

SQL Server
One of the most frequent questions you'll hear online is how to determine if a particular index is in use. There is no perfect answer to this question. You can look at the sys.dm_db_index_usage_stats to get a pretty good picture of whether or not an index is in use. However, this DMV has a few holes through which you could be mislead. I thought of another way to get an idea of how and where an index is being used. This is also a flawed solution, but, still, an interesting one. What if we queried the information in Query Store? Indexes Used in Query Store Now Query Store itself doesn't store index usage statistics. It stores queries, wait statistics and runtime metrics on individual queries. All useful stuff. Oh, and,…
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02Mar 2020 by Grant Fritchey 5 Comments

Query Store, Plan Forcing, and DROP/CREATE

SQL Server, T-SQL
I absolutely love Query Store and the ability it provides to force a plan is amazing. However, there are a lot of little gotchas in this functionality. I just recently found one that has quite a far reaching effect. Let's talk about what happens when you DROP and then CREATE a stored procedure. Query Store and Plan Forcing Let's quickly recap how Query Store works and how Plan Forcing works. First, Query Store is driven by query, not by procedure, not by batch, but by query. Second, plan forcing is also by query. However, there are queries and there are queries. Let's take this as an example: CREATE PROC dbo.AddressByCity @City NVARCHAR(30) AS BEGIN SELECT a.AddressID, a.AddressLine1, a.AddressLine2, a.City, sp.Name AS StateProvinceName, a.PostalCode FROM Person.Address AS a JOIN Person.StateProvince AS…
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21Jan 2020 by Grant Fritchey No Comments

Microsoft Tools That Help Query Tuning

SQL Server, T-SQL, Tools
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…
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12Aug 2019 by Grant Fritchey 6 Comments

Announcing a New Book: Query Store for SQL Server 2019

SQL Server
I'm pleased as punch to be able to share with you the fact that I helped Tracy Boggiano write a whole new book on Query Store. It will be available in October. You can pre-order it now. Tracy is a great author and a serious scholar of SQL Server. She's put together an excellent resource on Query Store. I added a couple of chapters just to help her out, but this is truly her book. Query Store is incredibly simple to use. It is however a bear to manage, so getting Tracy's book is a must if you're going to be implementing Query Store on your databases. By the way, you really should be implementing Query Store on your databases. Tracy covers all the topics from reporting with Query Store,…
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06May 2019 by Grant Fritchey 2 Comments

Query Store, Plan Forcing and Table Variables

SQL Server, T-SQL
This weekend I was in Stockholm in Sweden, talking Query Store and plan forcing with Steinar Anderson, when he mentioned the problems he had while forcing plans that had table variables in them. Don't panic. Of course you can force a plan with a table variable, most of the time. Steinar had a fairly focused problem. Before I go on to explain the issue, let me be really clear, Steinar figured out the issue all on his own. When he outlined the problem, I saw immediately what his conclusion was going to be. What's spurring this blog post is that Steinar said he'd searched on the internet and no one had talked about the issue yet. So, let's talk about it. Plan Forcing With Table Variables First up, let's show…
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25Mar 2019 by Grant Fritchey 1 Comment

Can You Force A Parallel Plan in Query Store?

SQL Server 2016, SQL Server 2017
I love the questions I get when presenting: Can You Force a Parallel Plan in Query Store. I haven't a clue. The trick I think is going to be in setting up the test. Let's try it out. Reliably Getting a Parallel Plan Because this is for testing, rather than try to build some crazy query that may or may not go parallel, I've decided to cheat. I'll take advantage of a little functionality that ensures I see a parallel plan when I want to. Here's my code: DBCC TRACEON(8649); GO SELECT soh.OrderDate, soh.ShipDate, sod.OrderQty FROM Sales.SalesOrderHeader AS soh JOIN Sales.SalesOrderDetail AS sod ON sod.SalesOrderID = soh.SalesOrderID WHERE soh.SalesOrderID = 43705; GO DBCC TRACEOFF(8649); Traceflag 8649 will force all plans to go parallel by effectively making the Cost Threshold for…
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11Mar 2019 by Grant Fritchey 4 Comments

Missing Indexes in the Query Store

SQL Server 2016, SQL Server 2017, T-SQL, Tools
I've shown before how to use the DMVs that read the plan cache as a way to connect the missing indexes suggestions with specific queries, but the other place to find missing index suggestions is the Query Store. Pulling from the Query Store The plans stored in the Query Store are exactly the same as the plans stored within the plan cache. This means that the XML is available and you can try to retrieve information from it directly, just as we did with the missing index queries against the DMVs. Here's the query modified for the Query Store: WITH XMLNAMESPACES (DEFAULT 'http://schemas.microsoft.com/sqlserver/2004/07/showplan') SELECT qsqt.query_sql_text, rts.plan_id, rts.NumExecutions, rts.MinDuration, rts.MaxDuration, rts.AvgDuration, rts.AvgReads, rts.AvgWrites, qsp.QueryPlan, qsp.QueryPlan.value(N'(//MissingIndex/@Table)[1]', 'NVARCHAR(256)') AS TableName, qsp.QueryPlan.value(N'(//MissingIndex/@Schema)[1]', 'NVARCHAR(256)') AS SchemaName, qsp.QueryPlan.value(N'(//MissingIndexGroup/@Impact)[1]', 'DECIMAL(6,4)') AS ProjectedImpact, ColumnGroup.value('./@Usage', 'NVARCHAR(256)') AS ColumnGroupUsage, ColumnGroupColumn.value('./@Name',…
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11Feb 2019 by Grant Fritchey 2 Comments

Query Store and a READ_ONLY Database

T-SQL, Tools
What happens in Query Store when the database itself is READ_ONLY? Yeah, I don't know. Let's find out. READ_ONLY The only way to find out how this works is to test it. So, let's write some code: CREATE DATABASE testquerystore; GO ALTER DATABASE testquerystore SET READ_ONLY; GO ALTER DATABASE testquerystore SET QUERY_STORE = ON; Executing that resulted in a small glitch in the Matrix: 8:00:54 AMStarted executing query at Line 1Commands completed successfully.8:00:54 AMStarted executing query at Line 2Commands completed successfully.8:00:54 AMStarted executing query at Line 5Msg 5004, Level 16, State 6, Line 5To use ALTER DATABASE, the database must be in a writable state in which a checkpoint can be executed.Msg 5069, Level 16, State 1, Line 5ALTER DATABASE statement failed.Total execution time: 00:00:01.448 Well that's not going to…
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