Search Results for: query store

Combining DMVs, Query Store and Extended Events Is Challenging

I was recently asked a question on a forum by a person who was frustrated with all the tool choices we have for measuring performance. Moreover, they were frustrated that a simple and clear combination of the tools to achieve synergy was extremely challenging. In fact, they said that, just using the query_hash as an example, they never saw a single match between the DMVs, Query Store and Extended Events. Now, that's pretty unlikely and I'm sure we could talk about why that might be the case. However, this idea of combining the tools, I shared a bunch of thoughts on it. I decided, maybe it's worth sharing here too. Achieving Synergy Honestly, this is tough. I work for a company that makes a monitoring tool. We are trying to…
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Find Indexes Used In Query Store

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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Query Store, Plan Forcing, and DROP/CREATE

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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Announcing a New Book: Query Store for SQL Server 2019

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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Query Store, Plan Forcing and Table Variables

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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Can You Force A Parallel Plan in Query Store?

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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Missing Indexes in the Query Store

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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Query Store and a READ_ONLY Database

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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Query Store and Plan Cache Plans Compared

Query Store plans and the plans in cache are identical, right? There won't be differences because the plan that is in cache is the plan that was used to execute the query. Similarly, the plan that is in the Query Store is the plan that was used to execute the query as well. Therefore, they will be the same. However, some small differences actually can show up. Differences Between Plans In order to compare the two plans, first, we need a query. Here's a stored procedure that I'm going to use to generate a plan that will be in cache and in the query store: CREATE 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…
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Query Store and Log Backups

A question that came up recently around Query Store is what happens when there are log backups in use on the database. Let's talk about it. Query Store and Log Backups The core of the answer is very simple. Query Store, like any other data written to a database, whether a system table or a user table, is a logged operation. So, when you backup the database, you're backing up Query Store data. When you backup the logs, you're also backing up Query Store data. A point in time will include all the data written to the Query Store at that point. However, that's the kicker. At what point was the Query Store information written to disk? By default, there's a fifteen minute cycle before the Query Store moves the…
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