SQL Server Reference Guide

Mar 28, 2003

␡

⎙ Print

< Back Page 181 of 365 Next >

We've arrived at the third phase of the Performance Tuning Audit. If you've been following along in this series then you have learned that one of the best ways you can tune a system is to create a systematic plan to evaluate your system from top to bottom. Having a plan helps you keep everything straight when the pressure is on, as it surely will be in a crisis. Having a documented process is even better, so I've created a four-step outline to help you work through your issues. You can find that outline explained in the first tutorial in this series.

But you will benefit even more if you develop your plan and implement it before you run into issues. The reason is that the audit creates a baseline you can work from when you do have system slowdowns. Comparing the metrics you collect when the system shows a performance issue with the baseline allows you to find changes in the metrics quickly, and more effectively direct your tuning efforts. Why fight a hardware issue when you have a poorly performing index?

At this phase of the process you've already defined your components and you've identified the individual items within those components to track. You've also learned how to select the objects and counters you need to monitor and track to create the second part of the process. As I've mentioned, how you store the results of the monitoring and the earlier component definitions is less important than the fact that you make the collections, and use tools readily available to everyone on your team. I'll cover the tools I recommend for the documentation and collection of the objects in another tutorial.

So you have a good idea about the layout of your system and a lot of data collected from multiple tools. All along I've cautioned you against watching the monitoring and then taking immediate action based on what you see. You, or other subject matter experts, will certainly find obvious corrections that you could make during the evaluation phase. Making those changes not only corrupts the test, they might mask other issues and dilute the effectiveness of the entire exercise. Of course, if there are issues which could cause major issues prior to the audit's completion, by all means correct them. But if the issue is such that you can wait, then you should wait until you’ve completed the phase I'm discussing in this section.

Another reason that you should wait until you have completed is that you should always work from as much intelligence as possible. If you've followed the process so far, you've got a great deal of information to work with — and you'll need it. The metrics you've collected don't have as much relevance by themselves as they do when combined with the documentation of each component. Here's a simple example to illustrate that point. I've examined the results of a system's monitoring that showed a high level of processor inefficiencies. At first glance, it seemed that the system needed a faster processor or more of them. When I examined the entire set of documentation, I found that the server was running Windows 2000, and it had hyper-threaded processors. Windows 2000 doesn't schedule threads onto a hyper-threaded processor in the most efficient way, so the interpretation was that the processor issue would benefit by installing an operating system such as Windows 2003 that works better with hyper-threading.

With all the information available from your earlier documentation efforts, start with the static information, specifically the layout drawings and/or documentation. Look for obvious "choke points" in the architecture, such as slow junctions in the network that use older or slower routers, and note those down. Also note any significant processing load in the design, and note down the servers in the architecture involved in that processing. Do the same thing for storage or memory requirements, from the design aspect.

Once you've noted these items, cross-reference the static information for the servers that you indicated in the design that have a heavy load. Do those servers appear to have adequate power to handle the load, or have newer servers crept into the landscape that could be rotated into that position? Now check the dynamic counters to see if the processors on those servers show a high load (above 70% utilization or so for more than a few minutes at a time). Check the metrics for the memory, storage access and other objects on those servers.

Now check the network dynamic information with the static information from those critical network junctions. Are there a high number of dropped packets showing on the routers or switches? Are you seeing a lot of CRC errors inside the WAN? Also check the latency to ensure you've got everything within tolerance.

Move on to the workstations. What you're looking for here is high resource use, such as processor, memory and storage loads. Also check for packet errors on the network interface.

If possible, you should try a representative operation from the application, such as a data entry or reporting query. Correlate the origination "click" from the workstation until the return packet on the screen. Using what you know from the landscape you can trace the packet from the client to the database and back – something called a "ripple". The dynamic information you collect during that timeframe will show where the highest lag is, and direct your tuning efforts.

In this phase you want to interpret the data you've collected. There are times when you can take the data and make direct statements about it — such as a high number of dropped packets on a network device. In those cases you can interpret that you have a networking issue. At other times you won't be able to make direct statements, because everything is working properly, or at least as efficiently as it can. In that case you might have to evaluate the system's design or the software calls. It's a little like driving to a location but taking the wrong route. There's nothing wrong with the driver, the car, or the road; it's just that you're taking the wrong path. Changing the path fixes the time problem.

It's not always as simple as "Watch this counter for this value. When it is X, the problem is Y." If that were the case, a tool could do the interpretation for you. Most of the time the answer is "it depends", which means you'll have to leverage your knowledge with others to find the issues. For instance, a latency of +600 milliseconds is normally an indicator of a network issue, but not always. In some cases this level of latency is acceptable with a properly architected application.

No matter what you encounter, write down what you think is wrong. Don't stop with the first red light that you see. Continue evaluating the system as a whole by examining the individual parts. Don't recommend corrections in this phase — that's next. Right now you're trying to say what is wrong — not what you need to do to fix the problem. Make a complete list and place it into your documentation.

In the next section I'll show you how to make suggestions for the fixes and how to create a plan to implement those fixes.

Informit Articles and Sample Chapters

The concepts I'm covering in this series aren't unique to databases. You'll find a great article here about characterizing your network layout here.

Online Resources

Did I pique your interest about hyperthreading processors and operating systems? Check out this article for more.

< Back Page 181 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