SQL Server Reference Guide

Mar 28, 2003

␡

⎙ Print

< Back Page 196 of 365 Next >

There are two primary methods for your tuning work. The first is the "manual" method. What you do here is examine as many system views, dynamic management views, performance counters and any other meta data you can find about what is happening on the system. You compile all that data, and then learn about what those numbers and responses mean when they line up in a certain way.

This method works great — in fact, for a performance tuning expert, this is the preferred way to work.

But some of us don't have time to be an expert in every arcane Performance Counter and Dynamic Management View (DMV), along with all the ways they can interact with the Query Processing engine with its Algebrizers, Parsers and so on, and the hardware and software configurations on the systems. Sure, we like to learn things in this area, but we have other work to do.

That brings up the second method — automatic tools. And automatic tools are good things — most of the time. Tools allow you to leverage far more work than you can without them, they automate processes that we might make errors in, and they do it far faster than we can. So it makes sense, even for an expert, to take some time and learn the automated tools we have in SQL Server to help us with performance.

But there are limits. If the tools could be blindly trusted, Microsoft would have built them into the engine's intelligence and just make the queries better to begin with. The very fact that they exist as a separate tool means that there is a time to use them and a time not to. In this tutorial we'll take a look at the SQL Server 2005 Database Tuning Advisor, and give some indication as to when to use it, and when to trust your own judgement.

SQL Server 2000 included a tool called the "Index Tuning Wizard". It would examine a query and suggest changes or additions to the indexes on a table or set of tables. That's great — as far as it goes. But there is far more involved in a tuning effort than just the indexes, as I've explained in my previous articles.

The other issue with the Index Tuning Wizard is that it needed fairly high permissions to run. If you wanted a DBA to tune only the databases they owned, they were out of luck unless they were the sysadmin on the whole box. In addition, the Index Tuning Wizard didn't always take everything into account. You could even trick it by running a query from one database in another!

A new tool was called for in SQL Server 2005. This tool is called the "Database Tuning Advisor", or DTA, and it goes much further in what it examines for the tuning suggestions. In addition, you can include any portions of the system you want the DTA to examine, and it will make suggestions just for those items.

So what will the DTA do for you? Well, Books Online tells us that the Database Engine Tuning Advisor can:

Recommend the best mix of indexes for databases by using the query optimizer to analyze queries in a workload.
Recommend aligned or non-aligned partitions for databases referenced in a workload.
Recommend indexed views for databases referenced in a workload.
Analyze the effects of the proposed changes, including index usage, query distribution among tables, and query performance in the workload.
Recommend ways to tune the database for a small set of problem queries.
Allow you to customize the recommendation by specifying advanced options such as disk space constraints.
Provide reports that summarize the effects of implementing the recommendations for a given workload.
Consider alternatives in which you supply possible design choices in the form of hypothetical configurations for Database Engine Tuning Advisor to evaluate.

So what does all that mean? Well, it means that the DTA goes a lot further in examining the whole system for your tuning efforts. But all this analysis depends a great deal on one thing: how well you represent the system to the DTA.

What this means is that the DTA has to "watch" activity on the system to see what to do to make it better. It's kind of like a golfing coach. If you tell the coach, "Whenever I hit the golf ball, it always arcs to the right." The coach can make a couple of guesses right from the start about what you're doing to cause that, but what he or she will probably tell you is "I need to watch your swing, and even better, watch you play an entire game." The reason they want to see that is that it provides lots of clues that they can use.

Suppose you swing the golf club one time for the coach. They might notice that your stance, or your grip, or your swing is causing you to "slice" the ball, meaning it will go to the right. But perhaps you do everything properly — at first. Perhaps after you've been playing for an hour or two on a hot golf course your grip relaxes, or you get too tired to swing properly.

What does all this have to do with the DTA? A lot. You can tell the DTA to watch three things: a query, a set of Profiler Trace Tables, or a Profiler Trace. I almost never use the query method. There's just too little data there, and it's like allowing the golf coach to only watch one swing. It's just not enough data to make any recommendations from.

So I normally use a SQL Server Trace file. In case you're not familiar with what that is, it is the output from the SQL Server Profiler, yet another tool (which I've described here) that can record the activity of SQL Server for you. You can include several items, like counters in the Windows Performance Monitor, which indicate system activity, both from the users and the system. Of course, you don't want to watch everything, because the system would take so much time recording every single event that it would affect the performance itself – which kind of defeats the purpose!

So which objects to collect? Ah — Microsoft thought about that. There's a "Trace Template" that you can choose called "Tuning" , which has everything the DTA needs to do its job.

But we're not finished yet. Not only do you need to collect the right items, you need to collect the right "profile" of activity. For instance, if you run the Profiler Trace on a weekend or when not many people are on, you won't stress the system to the point of failure, and the DTA needs to see the "real" problem to fix it. Think of the golf coach watching your entire game. The coach can then fix not only your swing but suggest some exercises to make your game that much better. The key, then, is collecting the right data, at the right times. That's what I focus on.

As far as running through the screens for the DTA — I don't think you need me to do that here. You have the information you need to get started, and the DTA is very simple to use. But you do need to know how to start it.

To start the DTA, you have a lot of options. It all depends on where you are when you want to run it. You'll find the tool listed on the Windows Start menu, and you can start it from there by clicking All Programs, then Microsoft SQL Server 2005, then Performance Tools, and then Database Engine Tuning Advisor.

You can also start the DTA in SQL Server Management Studio by selecting the Tools menu, and then selecting Database Engine Tuning Advisor.

But that's not all. You can also start the DTA from the SQL Server Management Studio Query Editor, inside a Transact-SQL script file. Just select a query in the Transact-SQL script, or select the entire script, and then right-click the selection. Now choose Analyze Query in Database Engine Tuning Advisor. The DTA will open and import the script as a workload. You can specify a session name and tuning options to tune the selected Transact-SQL queries as your workload.

One more — if you want to start the DTA in SQL Server Profiler, on the Tools menu, click Database Engine Tuning Advisor.

Here's how I use this amazing tool. I create my application, and then set up a test run, both automated and manual. I capture that activity on a very underpowered system and select all the options. I then parse out what I need to change, and see what change I get in performance when I run those test suites again. Notice I said "change" I get — not "increase". I've run the DTA and gotten a decrease in performance. There are a lot of reasons for that, but what I do is to un-check options and run the DTA again. It's pretty fast — the hard part is getting the Trace set up, and you already have that. I then follow the instructions and run my tests again. Usually there is one or two suggestions that "fight" over the right solution, and when I remove one them, the gain is worth the work.

Get out there and experiment — once you know how to use this powerful tool, you're a leg up on the performance problems you face.

< Back Page 196 of 365 Next >

🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Privacy Notice

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
Such marketing is consistent with applicable law and Pearson's legal obligations.
Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

As required by law.
With the consent of the individual (or their parent, if the individual is a minor)
In response to a subpoena, court order or legal process, to the extent permitted or required by law
To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
To investigate or address actual or suspected fraud or other illegal activities
To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020

Email Address