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APDEX

Core Apdex Qualities

I’m writing a series of posts about Generalizing Apdex. The previous post contains my plan of attack. This is #2.

Today, the Apdex specification focuses only on application responsiveness. To create a version of the Apdex standard that will apply in other measurement and reporting domains, we must:

  1. Generalize any language that refers to application responsiveness
  2. Identify the core qualities we want to preserve and promote
  3. Separate core Apdex rules from domain-specific rules

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Generalizing Apdex

Today the Apdex specification is entirely focused on application response time. Its first paragraph defines Apdex as “a method for calculating and reporting a metric of transactional application response time in the form of an index with a value of 0 to 1.” But in reality, the Apdex method is much more widely applicable, and a more appropriate description is already spelled out in the first paragraph of the Wikipedia article on Apdex:

(Apdex) defines a standard method for reporting and comparing the performance of software applications in computing. Its purpose is to convert measurements into insights about user satisfaction, by specifying a uniform way to analyze and report on the degree to which measured performance meets user expectations. — Referenced on May 7, 2010

Of course, there’s a good reason why Wikipedia reflects the broader view. Over the years, the idea of generalizing the Apdex standard to apply in other domains has been discussed periodically within the Apdex community. So when I created the Apdex wiki description in 2007, I already had those discussions in mind.

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Putting Apdex in Context

The Apdex method can play a useful role in any SLM process. But it is not the whole solution. Apdex is certainly a very useful tool when you have collected measurements and need a simple way to show how well those measurements reflect your goals. But first you have to decide what those goals should be.

This aspect of SLM is a broad subject that I’ve explored previously, for example:

The SERVQUAL Gaps Model

Today I was looking for a more systematic way to put Apdex in context, to focus on where Apdex can — and cannot — help. In the process, I discovered the SERVQUAL “gap” model, first defined in a 1985 paper, A Conceptual Model of Service Quality, by Parasuraman, Zeithaml, and Berry. There’s a link to a book and a (2.3Mb) copy of the original paper below. For a more concise and readable introduction online, I recommend the Theory Of The Gaps Model In Service Marketing, published by the Marketing Association of Australia and New Zealand.

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SLM With Apdex: Webinar Announcement

Webinar Date: Wednesday, May 12, 2010
Webinar Time: 12:00 noon EDT (1 hour)
Now available: Recording and slides

Overview

Speaker: Peter Sevcik, Executive Director Apdex Alliance

Service level management (SLM) is the art and science of keeping application services running properly once in production. The key to successful SLM is the ability to use metrics that are linked to the business.

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Don’t Expect Miracles from your Database Administrator

My previous post focused on the contribution of the Database Administrator (DBA) to application performance. Even so, application performance depends upon many factors, some of which are beyond the control of even the most dedicated DBA. So if you were thinking of relying on your DBA to fix everything, this week’s performance principle provides is intended as a wake-up call:

Expecting a DBA to guarantee the performance of any application that uses the database is like asking a piano tuner to guarantee a flawless performance, regardless of the pianist.

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Be Nice to a DataBase Administrator Today

The annual Computer History Museum Fellow Awards program publicly recognizes individuals of outstanding merit who have significantly contributed to advances in computing technology or applications, and to the evolution of the information age. Fellows may have worked in such diverse fields as hardware, software, networking, computer science, business, education, public service, or journalism, but they have one thing in common: their contributions have had a direct influence on computer history, and ultimately, they have changed our lives.

Each year around this time, a “who’s who” of the technology world assembles at the museum in Mountain View CA for a banquet and ceremony to induct a new group of Fellows. This evening, among the six new Fellows chosen in 2009, Don Chamberlin will be honored. Don was a co-inventor of SQL, the world’s most widely-used database language, and one of the managers of IBM’s System R project, which produced the first SQL implementation and seeded the development of much of IBM’s relational database technology.

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Monitor Standard Application Scenarios

In recent years, much has been written about the value of use cases and scenarios for capturing functional requirements; by comparison, their usefulness for performance management has received scant attention .  An application scenario defined for performance management purposes:

  • Involves a known fixed workload
  • Runs in the normal production environment
  • Runs against the production databases
  • Is instrumented to record response time

Because standard application scenarios are application/program instances with defined behaviors, their use of computing resources is also (relatively) predictable. In a sense, they are “benchmark” programs, since they perform a similar function. Normally however, performance benchmarks are designed to mimic a particular type of workload on a component or system, and are used to measure system capacity and throughput when processing a typically broad mix of applications.  Standard application scenarios, in contrast, can be designed to measure a system’s responsiveness for a single precisely-defined set of processing needs.

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Newton’s First Law of Performance Monitoring

If Sir Isaac Newton were stating the laws of computer systems performance, his first law would surely have been: The graph of performance continues in a straight line unless the force of some external event causes it to change.

Not knowing what changed is a serious impediment to problem diagnosis.

How does performance suddenly become “abnormal”? Of course, the answer is, it doesn’t–at least, not on its own. There is always an external cause. So to fix a performance problem, we must find the cause–usually more of something, such as:

  • Increased processing volumes
  • More data in a database
  • More customers
  • A new application competing for resources
  • Increased competition from existing applications on the same servers
  • Increased interference from other traffic on the network.

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Welcoming Chris Loosley

I would like to introduce Chris to the community.  A specialist in performance management, Chris is joining us as a regular contributor to the Apdex Exchange.  Through his work at IBM, Bachman, Database Associates, and Keynote Systems, Chris has helped to guide many organizations through the dangerous waters of software performance management.  He compiled his insights in High-Performance Client/Server, which is very informative book.  However, more important to this blog, Chris has had a hand in the development of Apdex from the ground up.  Chris was one of the co-editors of the original specification and has helped deliver the Apdex Symposium over the past three years.  I look forward to his contributions to this blog.

Using Apdex to Improve Online Customer Satisfaction

New Relic hosted a fast-paced webinar where Peter Sevcik, founder and executive director of the Apdex Alliance, provided an overview of Apdex. New Relic consultant Steve Hudson followed with real-world examples of how to measure Apdex scores in production Rails or Java web applications using RPM.

Click here to see the August 26 webinar in mp4 format.