24Mar 2015 by Grant Fritchey 3 Comments

Simple Parameterization and Data Types

SQL Server, T-SQL
Simple paramaterization occurs when the optimizer determines that a query would benefit from a reusable plan, so it takes the hard coded values and converts them to a parameter. Great stuff. But... Let's take this example. Here's a very simple query: SELECT ct.* FROM Person.ContactType AS ct WHERE ct.ContactTypeID = 7; This query results in simple parameterization and we can see it in the SELECT operator of the execution plan: We can also see the parameter that was defined in use in the predicate of the seek operation: Hang on. Who the heck put the wrong data type in there that's causing an implicit conversion? The query optimizer did it. Yeah. Fun stuff. If I change the predicate value to 7000 or 700000 I'll get two more plans and I…
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06Jan 2015 by Grant Fritchey 5 Comments

Execution Plans, Performance Tuning and Rum

Misc
[caption id="attachment_2827" align="alignleft" width="150"] This is me on the last cruise[/caption] In just a few more weeks I'll be setting sail on the first of two SQL Cruise events this year. I'm honored beyond my ability to appropriately express it to be included as one of the Technical Leads for both the cruise in February (7-14, 2015, I think there's a seat or two left) to the Caribbean and the one in June (14-21, 2015, definitely a couple of seats left) to the Mediterranean. Lest you think that this is just an excuse to hang out and drink, you ought to know a little about how sessions are presented on the cruise and the sessions I'm presenting. Don't mistake sessions on the boat for your typical one hour session at…
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15Jul 2014 by Grant Fritchey 2 Comments

Execution Plan Details

PASS, SQL Server, T-SQL
I wouldn't say it's common knowledge that you should look at execution plans when tuning queries, but it's not exactly uncommon knowledge either. But, people tend to get focused on just looking at the graphical part of the plan and there's just not enough information there. Let's take a look at a query: SELECT pc.Name, ps.Name, v.Name, pr.ReviewerName, p.Name, v.ModifiedDate, p.Color FROM Production.Product AS p LEFT JOIN Production.ProductReview AS pr ON pr.ProductID = p.ProductID JOIN Production.ProductSubcategory AS ps ON p.ProductSubcategoryID = ps.ProductSubcategoryID JOIN Production.ProductCategory AS pc ON pc.ProductCategoryID = ps.ProductCategoryID JOIN Purchasing.ProductVendor AS pv JOIN Purchasing.Vendor AS v ON v.BusinessEntityID = pv.BusinessEntityID ON pv.ProductID = p.ProductID WHERE v.ModifiedDate = '2006-02-17 00:00:00.000' AND p.Color LIKE 'Y%'; This generates an execution plan that looks like this: Neither v.ModifiedDate nor p.Color have indexes.…
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02Jul 2014 by Grant Fritchey 5 Comments

Statistics and Natively Compiled Procedures

T-SQL
Statistics are one of the single most important driving factors for the behavior of the query optimizer. The cardinality estimates stored within the statistics drive costing and costing drives the decision making of the optimizer. So, how does this work with the new SQL Server 2014 natively compiled procedures? Differently. In-memory tables do not maintain their statistics automatically. Further, you can't run DBCC SHOW_STATISTICS to get information about those statistics, so you can't tell if they're out of date or not or what the distribution of the data is within them. So, if I create some memory optimized tables, skip loading any data into them and then run this standard query: SELECT a.AddressLine1, a.City, a.PostalCode, sp.Name AS StateProvinceName, cr.Name AS CountryName FROM dbo.Address AS a JOIN dbo.StateProvince AS sp ON sp.StateProvinceID =…
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14Jan 2013 by Grant Fritchey 9 Comments

Execution Plans on Azure SQL Database Portal

Azure
If you've been working with the Azure SQL Database portal, you know that you have a query window. Within the query window you can run queries against your server. You'll get back results, timing, everything you need to observe behavior within the system. What's that? You never heard of this? Let's figure it out real quick. Here's my portal to my Azure SQL Databases: [caption id="attachment_2296" align="alignnone" width="150"] Azure SQL Database Portal showing usage overview[/caption] Yes, all sorts of things you can do from here, but we're focused on the bottom of the screen at the Manage button. Clicking this button will open up the Management portal window, part of which you can see below: [caption id="attachment_2298" align="alignnone" width="150"] Part of the Azure SQL Management Portal showing some of what…
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20Aug 2012 by Grant Fritchey 2 Comments

Another Execution Plan… In the Cloud!

Azure
A couple of weeks ago I posted about how different execution plans look when using the Azure Management Portal. I promised to look at a more complex plan and here we are. The query looks like this: SELECT * FROM dbo.Agent AS a JOIN dbo.Resource AS r ON a.AgentId = r.AgentId JOIN dbo.MovieStageResource AS msr ON r.ResourceId = msr.ResourceId JOIN dbo.MovieStage AS ms ON msr.Movieid = ms.MovieID AND msr.MovieStageDefinitionId = ms.MovieStageDefinitionId JOIN dbo.Movie AS m ON ms.MovieID = m.MovieId WHERE a.AgentId = 42; I didn't go nuts in creating a crazy complex query. I just wanted to see a standard set of different operators to see how things changed. As before, I'm working off a controlled database that has identical structures and data in both the Azure database and my…
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03Aug 2011 by Grant Fritchey 1 Comment

All About Execution Plans

PASS
If you’re attending the PASS Summit this October, I’d like to make a suggestion. The Summit itself is only three days long, Wednesday to Friday. But, if you have to travel any distance to get there, you’re going to miss work on Tuesday as well. Why not take a whole week away and spend Monday with Gail Shaw (blog|twitter) and me? The reason I ask is because Gail and I are putting together 7 hours of information all about execution plans. We’re going to be presenting this information on Monday at the Summit as a pre-conference seminar. Yes, you’ll have to pay extra to attend this session. But if you register for the Summit now, there’s still a discount, which you can put towards to the seminar. And, seriously now,…
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21Jan 2011 by Grant Fritchey 2 Comments

Deprecation, Trace and Execution Plans

SQL Server, T-SQL
As I’m sure you know, Microsoft occasionally changes it’s mind. Or, it makes bad decisions and then rectifies them. Or, it even reinforces bad decisions. Regardless of the purpose, the means by which these changes are implemented when they involve taking things away is deprecation. Usually in SQL Server the deprecation process is supposed to be over three releases. So while seeing something on the deprecation list can be cause for concern if it’s something you like, you certainly don’t need to panic. I’ve finally had a chance to start working with Denali and the place that concerned me most was in the areas of deprecation. I want to make sure that when I suggest a particular approach, that the approach isn’t going to disappear in a version or two.Which…
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18Nov 2010 by Grant Fritchey 18 Comments

Reason for Early Termination of Statement

SQL Server, T-SQL
Wouldn't you like to know why the optimizer stopped tuning the execution plan you're looking at? It's actually possible and simple to get this information. I talked about this a little more than a year ago, but I left out some information that might be useful. Let's take a very simple query: SELECT * FROM Person.Address AS a; This generates a simple execution plan, in fact a trivial plan: I know that this is a trivial plan one of two ways. The hard way is to look at the XML (BTW, this is the type of thing you can't see it in STATISTICS PROFILE, which I understand a lot of people are using). Right at the top is the SELECT element. You can see the value for StatementOptmLevel property is…
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04Oct 2010 by Grant Fritchey 1 Comment

How to Tell if Execution Plans are Reused

SQL Server, T-SQL
I try to watch the search phrases that point people to the blog because sometimes, you get a sense of what problems people are running into. The latest question or phrase I've seen a lot lately is along the lines of "how do you know if an execution plan is being reused." Since compiling an execution plan can be an extremely expensive operation, it's worth your time to understand how well a given plan is getting reused. If you've seen me present, I'll frequently talk about the application that had a query with an 86 table join. Recompiles on that thing were frequent and extremely costly. The only good news was, they were recompiles. If we weren't getting plan reuse it would have been an even worse system than it was. There are…
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