Click here to close now.

Welcome!

Java Authors: Liz McMillan, Carmen Gonzalez, Pat Romanski, Elizabeth White, Jnan Dash

Related Topics: Java, Microservices Journal, Virtualization, AJAX & REA

Java: Article

Why Response Times Are Often Measured Incorrectly

Response time measurements and how to interpret them

Response times are in many – if not in most – cases the basis for performance analysis. When they are within expected boundaries everything is ok. When they get to high we start optimizing our applications.

So response times play a central role in performance monitoring and analysis. In virtualized and cloud environments they are the most accurate performance metric you can get. Very often, however, people measure and interpret response times the wrong way. This is more than reason enough to discuss the topic of response time measurements and how to interpret them. Therefore I will discuss typical measurement approaches, the related misunderstandings and how to improve measurement approaches.

Averaging information away
When measuring response times, we cannot look at each and every single measurement. Even in very small production systems the number of transactions is unmanageable. Therefore measurements are aggregated for a certain timeframe. Depending on the monitoring configuration this might be seconds, minutes or even hours.

While this aggregation helps us to easily understand response times in large volume systems, it also means that we are losing information. The most common approach to measurement aggregation is using averages. This means the collected measurements are averaged and we are working with the average instead of the real values.

The problem with averages is that they in many cases do not reflect what is happening in the real world. There are two main reasons why working with averages leads to wrong or misleading results.

In the case of measurements that are highly volatile in their value, the average is not representative for actually measured response times. If our measurements range from 1 to 4 seconds the average might be around 2 seconds which certainly does not represent what many of our users perceive.

So averages only provide little insight into real world performance. Instead of working with averages you should use percentiles. If you talk to people who have been working in the performance space for some time, they will tell you that the only reliable metrics to work with are percentiles. In contrast to averages, percentiles define how many users perceived response times slower than a certain threshold. If the 50th percentile for example is 2.5 seconds this means that the response times for 50 percent of your users were less or equal to 2.5 seconds. As you can see this approach is by far closer to reality than using averages

Percentiles and Average of a Measurement Series

Percentiles and Average of a Measurement Series

The only potential downside with percentiles is that they require more data to be stored than averages do. While average calculation only requires the sum and count of all measurements, percentiles require a whole range of measurement values as their calculation is more complex. This is also the reason why not all performance management tools support them.

Putting all in a box
Another important question when aggregating data is which data you use as the basis of your aggregations. If you mix together data for different transaction types like the start page, a search and a credit card validation the results will only be of little value as the base data is kind of apple and oranges. So in addition to ensuring that you are working with percentiles it is necessary to also split transaction types properly so that the data that is the basis for your calculations fits together

The concept of splitting transactions by their business function is often referred to as business transaction management. While the field of BTM is wide, the basic idea is to distinguish transactions in an application by logical parameters like what they do or where they come from. An example would be a “put into cart” transaction or the requests of a certain user.

Only a combination of both approaches ensures that the response times you measure are a solid basis for performance analysis.

Far from the real world
Another point to consider with response times is where they are measured. Most people measure response times at the server-side and implicitly assume that they represent what real users see. While server-side response times are down to 500 milliseconds and everyone thinks everything is fine, users might experience response times of several seconds.

The reason is that server-side response times don’t take a lot of factors influencing end-user response times into account. First of all server-side measurements neglect network transfer time to the end users. This easily adds half a second or more to your response times.

Server vs. Client Response Time

Server vs. Client Response Time

At the same time server-side response times often only measure the initial document sent to the user. All images, JavaScript and CSS files that are required to render a paper properly are not included in this calculation at all. Experts like Steve Souders even say that only 10 percent of the overall response time is influenced by the server side. Even if we consider this an extreme scenario it is obvious that basing performance management solely on server-side metrics does not provide a solid basis for understanding end-user performance.

The situation gets even worse with JavaScript-heavy Web 2.0 applications where a great portion of the application logic is executed within the browser. In this case server-side metrics cannot be taken as representative for end-user performance at all.

Not measuring what you want to know
A common approach to solve this problem is to use synthetic transaction monitoring. This approach often claims to be “close to the end-user”. Commercial providers offer a huge number of locations around the world from where you can test the performance of pre-defined transactions. While this provides better insight into what the perceived performance of end-users is, it is not the full truth.

The most important thing to understand is how these measurements are collected. There are two approaches to collect this data: via emulators or real browsers. From my very personal perspective any approach that does not use real browsers should be avoided as real browsers are also what your users use. They are the only way to get accurate measurements.

The issue with using synthetic transactions for performance measurement is that it is not about real users. Your synthetic transactions might run pretty fast, but that guy with a slow internet connection who just wants to book a $5,000 holiday (ok, a rare case) still sees 10 second response times. Is it the fault of your application? No. Do you care? Yes, because this is your business. Additionally synthetic transaction monitoring cannot monitor all of your transactions. You cannot really book a holiday every couple of minutes, so you at the end only get a portion of your transactions covered by your monitoring.

This does not mean that there is no value in using synthetic transactions. They are great to be informed about availability or network problems that might affect your users, but they do not represent what your users actually see. As a consequence, they do not serve as a solid basis for performance improvements

Measuring at the End-User Level
The only way to get real user performance metrics is to measure from within the users’ browser. There are two approaches to do this. You can user a tool like the free dynaTrace Ajax Edition which uses a browser plug-in to collect performance data or inject JavaScript code to get performance metrics. The W3C now also has a number of standardization activities for browser performance APIs. The Navigation Timing Specification is already supported by recent browsers and the Resource Timing Specification. Open-source implementations like Boomerang provide a convenient way to access performance data within the browser. Products like dynaTrace UEM go further by providing a highly scalable backend and full integration into your server-side systems.

The main idea is to inject custom JavaScript code which captures timing information like the beginning of a request, DOM ready and fully loaded. While these events are sufficient for “classic” web applications they are not enough for Web 2.0 applications which execute a lot of client-side code. In this case the JavaScript code has to be instrumented as well.

Is it enough to measure on the client-side?
The question now is whether it is enough to measure performance from the end-user perspective. If we know how our web application performs for each user we have enough information to see whether an application is slow or fast. If we then combine this data with information like geo location, browser and connection speed we know for which users a problem exists. So from a pure monitoring perspective this is enough.

In case of problems, however, we want to go beyond monitoring. Monitoring only tells us that we have a problem but does not help in finding the cause of the problem. Especially when we measure end-user performance our information is less rich compared to development-centric approaches. We could still use a development-focused tool like dynaTrace Ajax Edition for production troubleshooting. This however requires installing custom software on an end user’s machine. While this might be an option for SaaS environments this is not the case in a typical eCommerce scenario.

The only way to gain this level of insight for diagnostics purposes is to collect information from the browser as well as the server side to have a holistic view on application performance. As discussed using averaged metrics is not enough in this case. Using aggregated data does not provide the insight we need. So instead of aggregated information we require the possibility to identify and relate the requests of a user’s browser to server-side requests.

Client/Server Drill Down of Pages and Actions

Client/Server Drill Down of Pages and Actions

The figure below shows an architecture based (and abstracted) from dynaTrace UEM which provides this functionality. It shows the combination of browser and server-side data capturing on a transactional basis and a centralized performance repository for analysis.

 

Architecture for End-To-End User Experience Monitoring

Architecture for End-To-End User Experience Monitoring

Conclusion
There are many ways where and how to measure response times. Depending on what we want to achieve each one of them provides more or less accurate data. For the analysis of server-side problems measuring at the server-side is enough. We however have to be aware that this does not reflect the response times of our end users. It is a purely technical metric for optimizing the way we create content and service requests. The prerequisite to meaningful measurements is that we separate different transaction types properly.

Measurements from anything but the end-user’s perspective can only be used to optimize your technical infrastructure and only indirectly the performance of end users. Only performance measurements in the browser enable you to understand and optimize user-perceived performance.

Related reading:

  1. Antivirus Add-On for IE to cause 5 times slower page load times The dynaTrace AJAX Community has been really active lately –...
  2. Troubleshooting response time problems – why you cannot trust your system metrics // Production Monitoring is about ensuring the stability and health...
  3. Why you can’t compare cross browser execution times of Selenium Tests // I am currently working on a blog where I...
  4. Application Performance Monitoring in production – A Step-by-Step Guide – Part 1 // Setting up Application Performance Monitoring is a big task,...
  5. Week 9 – How to Measure Application Performance Measurement is the most central concept in any performance-related activity....

More Stories By Alois Reitbauer

Alois Reitbauer works as a Technology Strategist for dynaTrace Software where he is leading the Methods and Technology team. As part of the R&D team he influences the dynaTrace product strategy and works closely with key customers in implementing performance management solution for the entire lifecylce. Alois has 10 years experience as architect and developer in the Java and .NET space. He is a frequent speaker at technology conferences on performance and architecture related topics and regularly publishes articles blogs on blog.dynatrace.com

@ThingsExpo Stories
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
SYS-CON Events announced today that SoftLayer, an IBM company, has been named “Gold Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place June 9-11, 2015 at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place November 3–5, 2015 at the Santa Clara Convention Center in Santa Clara, CA. SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from ...
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborate. Cisco and our partners are building the platform for the Internet of Everything by connecting the...
SYS-CON Events announced today that Liaison Technologies, a leading provider of data management and integration cloud services and solutions, has been named "Silver Sponsor" of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York, NY. Liaison Technologies is a recognized market leader in providing cloud-enabled data integration and data management solutions to break down complex information barriers, enabling enterprises to make smarter decisions, faster.
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.
SYS-CON Events announced today that Open Data Centers (ODC), a carrier-neutral colocation provider, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Open Data Centers is a carrier-neutral data center operator in New Jersey and New York City offering alternative connectivity options for carriers, service providers and enterprise customers.
SYS-CON Events announced today that On the Avenue Marketing Group, a sales and marketing firm that utilizes events to market and sell products to consumers, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. On the Avenue Marketing Group (OTA) is a sales and marketing firm that utilizes events to market and sell products to consumers. On behalf of our clients, we attend thousands of fairs, festivals, expos, concerts, conferences, and sporting events annually, helping them reach millions of individuals ...
SYS-CON Events announced today that ActiveState, the leading independent Cloud Foundry and Docker-based PaaS provider, has been named “Silver Sponsor” of SYS-CON's DevOps Summit New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. ActiveState believes that enterprises gain a competitive advantage when they are able to quickly create, deploy and efficiently manage software solutions that immediately create business value, but they face many challenges that prevent them from doing so. The Company is uniquely positioned to help address these challenges thro...
SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
SYS-CON Events announced today that Alert Logic, the leading provider of Security-as-a-Service solutions for the cloud, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® and DevOps Summit 2015 New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo® and DevOps Summit 2015 Silicon Valley, which will take place November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that kintone has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. kintone promotes cloud-based workgroup productivity, transparency and profitability with a seamless collaboration space, build your own business application (BYOA) platform, and workflow automation system.
SYS-CON Events announced today that Akana, formerly SOA Software, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Akana’s comprehensive suite of API Management, API Security, Integrated SOA Governance, and Cloud Integration solutions helps businesses accelerate digital transformation by securely extending their reach across multiple channels – mobile, cloud and Internet of Things. Akana enables enterprises to share data as APIs, connect and integrate applications, drive part...
SYS-CON Events announced today that CommVault has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. A singular vision – a belief in a better way to address current and future data management needs – guides CommVault in the development of Singular Information Management® solutions for high-performance data protection, universal availability and sim...
SYS-CON Events announced today that SafeLogic has been named “Bag Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SafeLogic provides security products for applications in mobile and server/appliance environments. SafeLogic’s flagship product CryptoComply is a FIPS 140-2 validated cryptographic engine designed to secure data on servers, workstations, appliances, mobile devices, and in the Cloud.
SYS-CON Events announced today that StorPool Storage will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. StorPool is distributed storage software that allows service providers, enterprises and other cloud builders to run data storage on standard x86 servers, instead of using expensive and inefficient storage arrays (SAN).
SYS-CON Events announced today that Site24x7, the cloud infrastructure monitoring service, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Site24x7 is a cloud infrastructure monitoring service that helps monitor the uptime and performance of websites, online applications, servers, mobile websites and custom APIs. The monitoring is done from 50+ locations across the world and from various wireless carriers, thus providing a global perspective of the end-user experience. Site24x7 supports monitoring H...
SYS-CON Events announced today that Intelligent Systems Services will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Established in 1994, Intelligent Systems Services Inc. is located near Washington, DC, with representatives and partners nationwide. ISS’s well-established track record is based on the continuous pursuit of excellence in designing, implementing and supporting nationwide clients’ mission-critical systems. ISS has completed many successful projects in Healthcare, Commercial, Manufacturing, ...
SYS-CON Events announced today that B2Cloud, a provider of enterprise resource planning software, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. B2cloud develops the software you need. They have the ideal tools to help you work with your clients. B2Cloud’s main solutions include AGIS – ERP, CLOHC, AGIS – Invoice, and IZUM
SYS-CON Events announced today that Vicom Computer Services, Inc., a provider of technology and service solutions, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. They are located at booth #427. Vicom Computer Services, Inc. is a progressive leader in the technology industry for over 30 years. Headquartered in the NY Metropolitan area. Vicom provides products and services based on today’s requirements around Unified Networks, Cloud Computing strategies, Virtualization around Software defined Data Ce...