Home > Articles > Programming

Analyzing Performance-Testing Results to Correlate Performance Plateaus and Stress Areas

Mike Kelly builds on Scott Barber's work to show how you can combine performance-degradation curves and complex performance scenarios to help determine "good enough" quality for an application in terms of performance.
Mike Kelly builds on Scott Barber's work to show how you can combine performance-degradation curves and complex performance scenarios to help determine "good enough" quality for an application in terms of performance.
Like this article? We recommend

A year or so ago I had the pleasure of attending a conference at which Scott Barber gave two presentations on performance testing. The first presentation was on the effective presentation of performance test data; the second was on the modeling of application user communities. After watching both presentations and talking with Scott, I was able to draw a couple of insights. First, many times we focus too much on the problems that are easy to identify, rather than taking the time to determine where the real problems may be hiding. Second, we tend to performance test for the sake of performance testing, rather than taking the time to understand the usage of the application and the business drivers within which it operates. This behavior results in not knowing what to test and in not understanding how much performance testing is enough for the application.

In this article, I'll build on some of Scott's work to show how we can combine performance-degradation curves and complex performance scenarios to help determine "good enough" quality for an application in terms of performance. Throughout the article, I'll refer to Scott's work by providing a quick summary and stealing an example for illustration, and then move on to the next topic. I leave it to you to do the research necessary to fully understand the summarized content. This article is intended for the experienced performance tester or test manager.

Performance-Degradation Curves

Before we jump into the guts of this article, it might be good to establish some working definitions and concepts. Let's start with performance-degradation curves. In his article on creating a performance degradation curve, Scott Barber outlines a basic response-time degradation curve. If you're not familiar with this work, take a minute to read that article first; it sets the stage for what we're about to cover.

Figure 1 is an example of a response-time degradation curve. Degradation curves are common among performance testers; they go by various names, so forgive me if you know this curve by another name. A response-time degradation curve plots the response time experienced by the user against the user load. It's worth pointing out that the various user loads represented on one of these plots all use the same user-community model (explained in more detail later in this article). Later on, I'll discuss how to compare loads based on different models. This example shows the response times for two web pages (the home page and page 1) under differing loads (from 1 to 200 users). Curves like the one in Figure 1 are good for comparing specific page-response times across multiple tests using the same model, graphically displaying where performance starts to decline and where performance becomes unacceptable.

Figure 1

Figure 1 A basic response-time degradation curve.

The shape of a typical response-time degradation curve can be broken down into four regions (see Figure 2):

  • The single-user region is just that—the response time for a single user on the system. This is useful for establishing a point of reference.
  • The performance plateau shows the best performance you can expect under the specific conditions of that particular test without further performance tuning. This area represents good candidates for baselines and/or benchmarks.
  • The stress region is where the application "degrades gracefully." Typically, the max recommended user load is the beginning of the stress region.
  • The knee in performance is the point where performance "degrades ungracefully."
Figure 2

Figure 2 Four regions of the response-time degradation curve.

These regions are typically used by testers to help them determine where performance starts to degrade for any given portion of the application. It has been my experience that these charts are used primarily for two purposes:

  • The effective display of performance information, in an effort to show "good enough" performance or poor performance in relation to some stated requirement. For example, if I had a requirement stating that the home page must load in under six seconds with 100 concurrent users, I could confirm that requirement using the chart in Figure 2. If the requirement was for 200 users, I could use the same graph to show that more work needs to be done to meet the requirement.
  • As a tool used to determine the knee in performance while performance tuning. Where the knee occurs is the absolute maximum load you ever want your application/system to encounter. Data collected after the knee is the load data that exploits your critical bottleneck; this data is then used to research and correct performance bottlenecks. Many times this is an iterative process in an effort to push the knee in performance further to the right (or to a higher load).

While many testers are interested in the stress region and the knee in performance, in this article we'll take a slightly different view on this data.

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.


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.


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.


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.


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


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


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.


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.


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