Software QA FYI - SQAFYI

How Fast Does a Website Need To Be?

By: Scott Barber

Abstract. Since at least the late 1990ís, many web development organizations have been asking the question ďWhat is the industry standard response time for a web page?Ē As a result various attempts have been made to create such a standard, but none of these standards have been generally accepted Ė largely because every web user has a different personal feeling about whether a particular web page is responsive enough to be considered ďacceptableĒ. This paper demonstrates why a blanket response time standard is not the best answer in terms of design criteria and explores the critical items that need to be considered in determining appropriate response time goals for websites.

1. Introduction
As an active member of the international Performance Testing community and as an experienced practitioner, I have seen questions like this one posed numerous times:

"Iím desperately trying to find out what the industry standard response times are. What are reasonable benchmarks that are acceptable for Web sites at the moment? Is 1.5 seconds a reasonable target????"
My answer to questions like this one always starts with "It depends on . . . " My friend Joe Strazzere addressed this particular question quite well on a popular internet forum, as follows:

There are no industry standards. You must analyze your site in terms of who the customers are, what their needs are, where they are located, what their equipment and connection speed might be, etc., etc. I suspect 1.5 seconds would be a rather short interval for many situations. Do you really require that quick of a response?[1]

The bottom line is that what seems fast is different in different situations. So how do you determine how fast is fast enough for your application, and how do you convert that information into explicit, testable requirements? Those are the topics this article addresses.

2. Considerations Affecting Performance Expectations
Letís start by discussing the leading factors that contribute to what we think fast is. I believe these considerations can be divided into three broad categories:
ē user psychology
ē system considerations
ē usage considerations

None of these categories is any more or less important than the others. Whatís critical is to balance these considerations, which weíll explore individually here, when determining performance requirements.

2.1. User Psychology
Of the three categories, user psychology is the one most often overlooked Ė or maybe a better way to say this is that user psychology is often overridden by system and usage considerations. I submit that this is a mistake. User psychology plays an important role in perceived performance, which is the most critical part of evaluating performance.

Consider this example. I recently filled out my tax return online. Itís a pretty simple process: you navigate through a Web application that asks you questions to determine which pages are presented for you to enter data into. As I made a preliminary pass through my return, I was happy with the performance (response time) of the application. When I later went back to complete my return, I timed the page loads (because I almost always think about performance when I use the Internet). Most of the pages returned in less than 5 seconds, but some of the section summary pages took almost a minute! Why didnít I notice the first time through that some pages were this slow? Why didnít I get frustrated with this seemingly poor performance? I usually notice performance as being poor at between 5 and 8 seconds, and at about 15 seconds Iíll abandon a site or at least get frustrated. Thereís no science behind those numbers; theyíre just my personal tolerance levels. So what made me wait a minute for some pages without even noticing that it was slow? The answer is that when I requested a section summary page, an intermediate page came up that said:

"The information you have requested is being processed. This may take several minutes depending on the information you have provided. Please be patient."

When I received that message, I went on to do something else for a minute. I went to get a drink, or checked one of my email accounts, or any of a million other things, and when I came back the page was there waiting for me. I was satisfied. If that message hadnít been presented and I had found myself just sitting and waiting for the page to display, I would have become annoyed and eventually assumed that my request wasnít submitted properly, that the server had gone down, or maybe that my Internet connection had been dropped.

So, getting back to the initial question of how fast is fast enough, from a user psychology perspective the answer is still "it depends." It depends on several key factors that determine what is and isnít acceptable performance.

The first factor is the response time that users have become accustomed to based on previous experience. This is most directly tied to the speed of their Internet connection. My mother, for example, has never experienced the Internet over anything other than a fuzzy phone line with a 56.6-kilobytes-per-second modem. Iím used to surfing via high-speed connections, so when I sign on at my motherís house Iím frustrated. My mother thinks Iím silly: "Scott, I think youíre spoiled. Thatís as fast as we can get here, and a lot faster than we used to get! You never were very patient!" Sheís right Ė Iím not very patient, so I have a low tolerance for poor Web site performance, whereas she has a high tolerance.
Another factor is activity type. All users understand that it takes time to download an MP3 or MPEG video, and therefore have more tolerance if theyíre aware that thatís the activity theyíre performing. However, if users donít know that theyíre performing an activity like downloading a file and are just waiting for the next page to load, theyíre likely to become frustrated before they realize that the performance is actually acceptable for the activity theyíre performing.
This leads us to the factor of how user expectations have been set. If users know what to expect, as they do with the tax preparation system I use, theyíre likely to be more tolerant of response times they might otherwise think of as slow. If you tell users that the system will be fast and then it isnít, they wonít be happy. If you show users how fast it will be and then follow through with that level of performance, theyíll generally be pretty happy.
The last factor we should discuss here is what I call surfing intent. When users want to accomplish a specific task, they have less tolerance for poor performance than when theyíre casually looking for information or doing research. For example, when I log on to the site I use to pay bills, I expect good performance. When Iím taking a break from work and searching for the newest technology gadgets, I have a lot of tolerance for poor performance.
So with all of these variables you can see why, as Joe Strazzere said, "There are no industry standards." But if there are no industry standards, how do we know where to start or what to compare against? Iíll describe some rules of thumb later, when we get to the topic of collecting information about performance requirements.

2.2. System Considerations
System considerations are more commonly thought about than user psychology when weíre determining how fast is fast enough. Stakeholders need to decide what kind of performance the system can handle within the given parameters. "Fastenough" decisions are often based purely on the cost to achieve performance. While cost and feasibility are important, if theyíre considered in a vacuum, youíll be doomed to fielding a system with poor performance.
Performance costs. The cost difference between building a system with "typical" performance and building a system with "fast" performance is sometimes prohibitive. Only by balancing the need for performance against the cost can stakeholders decide how much time and/or money theyíre willing to invest to improve performance.

System considerations include the following:
ē system hardware
ē network and/or Internet bandwidth of the system
ē geographical replication
ē software architecture

Entire books are dedicated to each of these considerations and many more. This is a well-documented and well-understood aspect of performance engineering, so I wonít spend more time on it here.

2.3. Usage Considerations
Usage considerations are related to but separate from user psychology. The usage considerations Iím referring to have to do with the way the Web site or Web application will be used. For example, is the application a shopping application? An interactive financial planning application? A site containing current news? An internal human resources data entry application? "Fast" means something different for each of these different applications. An application thatís used primarily by employees to enter large volumes of data needs to be faster for users to be satisfied than a Web shopping site. A news site can be fairly slow, as long as the text appears before the graphics. Interactive sites need to be faster than mostly static sites. Sites that people use for work-related activities need to be faster than sites that are used primarily for recreational purposes.

These considerations are very specific to the site and the organization. There really isnít a lot of documentation available about these types of considerations because theyíre so individual, depending on the specific application and associated user base. Whatís important is to think about how your site will be used and to determine the performance tolerance of expected users as compared to overall user psychology and system considerations. Iíll say more about this in the next section.

3. Collecting Information About Performance Requirements
So how do you translate the considerations described above into performance requirements? My approach is to first come up with descriptions of explicit and implied performance requirements in these three areas:

ē user expectations
ē resource limitations
ē stakeholder expectations

In general, user and stakeholder expectations are complementary and donít require balancing between the two. For this reason, I start by determining these requirements. Once Iíve done this, I try to balance those with the system/financial resources that are available. Truth be told, I generally donít get to do the balancing. I usually collect the data and identify the conflicts so that stakeholders can make decisions about how to balance expectations and resources to determine actual requirements.

Determining the actual requirements in the areas of speed, scalability, and stability and consolidating these into composite requirements is the final step. Iíll describe that process in detail later on, but first letís look at each of the three areas where youíll be collecting information about requirements.

3.1. User Expectations
A userís expectations when it comes to performance are all about end-to-end response time, as we touched on earlier in our look at user psychology. Individual users donít know or care how many users can be on the system at a time, how the system is designed to recover in case of disaster, or what the cost of building and maintaining the system has been. When a new system is replacing an old one, itís critical from the userís perspective for the requirements of the new system to be at least as stringent as the actual performance of the existing system. Users wonít be pleased with a new system if their perception is that its performance is worse than the system itís replacing Ė regardless of whether the previous system was a Web-based application, client/server, or some other configuration.

Aside from this situation, thereís no way to predict user expectations. Only users can tell you what they expect, so be sure you take the time to poll users and find out what their expectations are before the requirements are set. Talk to users and observe them using a similar type of system, maybe even a prototype of the system to be built. Remember that most users donít think in terms of seconds, so to quantify their expectations youíll have to find a way to observe what they think is fast, typical, or slow.

During my tenure as a performance engineer, Iíve done a lot of research in the area of user expectations. I believed at first in the "8-second rule" that became popular in the mid-1990s, simply stating that most Web surfers consider 8 seconds to be a reasonable download time for a page. But since then Iíve found no reliable research backing this rule of thumb, nor have I found any correlation between this rule of thumb and actual user psychology. Iím going to share with you what I have found, not to suggest these findings as standards but to give you a reasonable place to start as you poll your own users. Iíve found that most users have the following expectations for normal page loads when surfing on high-speed connections:

ē no delay or fast Ė under 3 seconds
ē typical Ė 3 to 5 seconds
ē slow Ė 5 to 8 seconds
ē frustrating Ė 8 to 15 seconds
ē unacceptable Ė more than 15 seconds

In my experience, if your site is highly interactive or primarily used for data entry you should probably strive for page load speeds about 20% faster than those listed. For mostly static or recreational sites, performance thatís about 25% slower than the response times listed may still be acceptable.

For any kind of file download (MP3s, MPEGs, and such):
ē If the link for the file includes a file size and the download has a progress bar, users expect performance commensurate with their connection speed.
ē If users are unaware theyíre downloading a file, the guidelines for normal pages apply. For other activity:
ē Unless user expectations are set otherwise, the guidelines for normal pages apply.
ē If users are presented with a notice that this may take a while, theyíll wait significantly longer than without a notice, but the actual amount of time theyíll wait varies drastically by individual.
When users are made aware of their connection speed, their expectations about performance shift accordingly. Part of my experiments with users was to create pages with the response times in each of the categories above over a high-speed connection, then to throttle back the connection speed and ask the users the same questions about performance. As long as I told them the connection rate I was simulating, users rated the pages in the same categories, even though the actual response times were very different.

One final note: Thereís a common industry perception that pages that users find "typical" or "slow" on high-speed connections will be "frustrating" or "unacceptable" to users on slower connections. My research doesnít support this theory. It does show that people who are used to high-speed connections at work but have slower dial-up connections at home are often frustrated at home and try to do Internet tasks at work instead. But people who are used to slower connections rate the same pages as fast, typical, slow, and unacceptable over their typical connection as people who are used to high-speed connections and try to load these pages over their typical connection.

3.2. Resource Limitations
Limitations on resources such as time, money, people, hardware, networks, and software affect our performance requirements, even though we really wish they didnít. For example, "You canít have any more hardware" is a resource limitation, and whether we like it or not, it will likely contribute to determining our requirements.
Anecdotally, thereís a lot to say about the effects of resource limitations on performance requirements, but practically all it really comes down to is this: Determine before you set your performance requirements what your available resources are, so that when youíre setting the requirements, you can do so realistically.

3.3. Stakeholder Expectations
Unlike user expectations, stakeholder expectations are easy to obtain. Just ask any stakeholder what he or she expects. "This system needs to be fast, it needs to support ten times the current user base, it needs to be up 100% of the time and recover 100% of the data in case of down time, and it must be easy to use, make us lots of money, have hot coffee on my desk when I arrive in the morning, and provide a cure for AIDS."
OK, thatís not something an actual stakeholder would say, but thatís what it feels like they often say when asked the question. Itís our job to translate these lofty goals into something quantifiable and achievable, and thatís not always an easy task. Usually stakeholders want "industry standards as written by market experts" to base their expectations on. As weíve already discussed, there are no standards. In the absence of standards, stakeholders generally want systems so fast and scalable that performance becomes a nonissue . . . until they find out how much that costs.
In short, stakeholders want the best possible system for the least possible money. This is as it should be. When it comes to stakeholders, itís our job to help them determine, quantify, and manage system performance expectations. Of the three determinants of performance requirements that weíve been discussing, the stakeholders have both the most information and the most flexibility. User expectations very rarely change, and resource limitations are generally fairly static throughout a performance testing/engineering effort. Stakeholder expectations, however, are likely to change when decisions have to be made about tradeoffs.
Consider this. Recently Iíve been involved with several projects replacing client/server applications with Web-based applications. In each case, the systems were primarily data entry systems. Initially, stakeholders wanted the performance of the new application to match the performance of the previous client/server application. While this is in line with what I just said about user expectations, itís not a reasonable expectation given system limitations. Web-based systems simply donít perform that fast in general. And Iíve found that even users who are accustomed to a subsecond response time on a client/server system are happy with a 3-second response time from a Web-based application. So Iíve had stakeholders sit next to users on the prototypes (that were responding in 3 seconds or less) and had those users tell the stakeholders how they felt about performance. When stakeholders realize that users are satisfied with a "3-second application," theyíre willing to change the requirement to "under 3 seconds."
Speed, of course, isnít the only performance requirement. Stakeholders need to either inform you of what the other requirements are or be the final authority for making decisions about those requirements. Itís our job to ensure that all of the potential performance requirements are considered Ė eve

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How Fast Does a Website Need To Be?