Welcome!

Industrial IoT Authors: William Schmarzo, Elizabeth White, Stackify Blog, Yeshim Deniz, SmartBear Blog

Related Topics: Java IoT, Industrial IoT, Microservices Expo, Microsoft Cloud, Machine Learning

Java IoT: Article

An Introduction to Client Latency

Speed as perceived by the end user is driven by multiple factors, including how fast results are returned

What is client latency?
Let's face it, users are impatient. They demand a blazingly fast experience and accept no substitutes. Google performed a study in 2010 which proved that when a site responds slowly, visitors spend less time there.

Speed as perceived by the end user is driven by multiple factors, including how fast results are returned and how long it takes a browser to display the
content.

So while the effects of poor performance is obvious, it makes one wonder about the relationship between client latency and the "perception of speed". After all, the user can trigger many state change events (page load, submit a form, interact with a visualization, etc) and all these events have an associated latency to the client. However, are certain types of latency more noticable to the user then others?

Let's look at all the different ways latency can creep in, throughout the ‘request-to-render' cycle.

Time To First Lag
The first place for potential client latency is the infamous Time To First Byte. From a user perspective, this is the worst kind of client latency, as it leaves the user with the dreaded "white screen of death".

WSoD

"White Screen of Death" in Google Chrome

Time To First Byte (TTFB) is the duration between a user making an HTTP request and first byte of the page being received by the browser. The following is a typical scenario for TTFB:

2 seconds to first byte ... but at least everything else is fast!

Two seconds to first byte ... but at least everything else is fast!

  • User enters a URL in browser and hits enter
  • The browser parses the URL
  • The browser performs a DNS lookup (Domain => IP address)
  • The browser opens a TCP connection and sends the HTTP Request
  • (Wait on the network)
  • The browser starts receiving the HTTP Response (first byte received)

As you can see, there are many places in this segment where latency can rear it's ugly head. The DNS lookup may fail, the web server may be under heavy load so it'squeueing requests, network channel congestion may be causing packet loss, or soft errors due to cosmic rays flipping bits.

This type of latency has negative effects on the user, as the user gets stuck looking at a loading/waiting animation. This becomes a true test of the user's patience, as an long TTFB can eventually lead the user to abandon the HTTP Request and close the browser tab.

Client Latency and the DOM
Now that the HTTP Response is pouring in, the browser engine can start doing what it does best...display content! But before the browser can render (or paint) content on the screen, there is still more work to be done!

NOTE: Not all browsers engines are created equal! Consult your local open source browser source code repository for detailed inner workings.

As the browser engine receives HTML, it begins constructing the HTML DOM tree. While parsing the HTML and building the DOM tree, the browser is looking for any
assets (or sub-resources) so it can initiate a download of their content.

So now that the HTTP Response has arrived, let's take a further look into the associated latency for both CSS and Javascript sub-resource and how it effects the user experience.

CSS
CSS related latency gives the user the impression of a "broken page". This comes in two forms, a "flash of unstyled content" (FOUC) where the page appears unstyled for a short period, then it flickers into the right design. However, if the stylesheet never loads, the DOM content will just remain unstyled. While this isn't ideal, its manageable because content is still available to the user but just in a degraded state.

Let's look at the effect of latency on styling and rendering the DOM.

browser_render

  • The browser is parsing the HTML in the HTTP Reponse
  • When the browser locates a link tag, it initiates a non-blocking download of the external CSS stylesheet
  • (Wait on network)
  • Once the download completes, the browser engine begins to parse the CSS
  • While parsing CSS, the browser engine is building all the CSS style rules and begins matching DOM elements to CSS styles
  • Once complete, the browser engine then applys the style rules with the DOM nodes by constructing a render tree
  • This builds a layout, which the browser then renders or paints to the screen

Latency in this segment is highly visible to the user, as it's the last hurdle to overcome before we can actually display content to the user. The first potential bottleneck is the placement of the stylesheet tag. We want the stylesheet to be downloaded as soon as possible, so we can progressively render the page. Thus, use your HEAD and Put stylesheets at the Top. The user-visible effect of not following this is a "flash of unstyled content" or a "white screen of death" (depending on the browser).

Our next stop on the latency express is the network. We always want to use an external stylesheet, however this requires an extra download. So we want this download to be fast, optimized for user location, and highly reliable. Well if you haven't been living under a rock, then you know to Use a Content Delivery Network (CDN). The user-visible effect of not following is slower loading of styled content, as your webserver has to handle extra requests to serve the assets (increased load) and this can be slower for users in geographically distant locations.

Finally, we have how you write your CSS as the last chokepoint. Inefficiently written CSS causes the browser to take longer to build a complete render tree, thus the user-visible effect is a slower loading page render. Fortunately, this is easily avoidable if you just Write efficient CSS.

Following CSS best practices will not only improve your user experience but also provide your users with the appearance that your pages are loading faster.

JavaScript
JavaScript related latency can have differing effects on the user experience. Clicking links that don't seem to do anything, stalled loading of the page, or a "laggy" feeling when scrolling through a page.

There are many places where client latency can appear with Javascript, so let's take ahighly simplified look at how the browser deals with Javascript.

  • The browser is parsing the HTML in the HTTP Reponse
  • When the browser locates a script tag, it initiates a blocking download of the external Javascript file
  • (Wait on network)
  • The browser parses the Javascript file
  • The browser executes the Javascript file
  • (The browser is no longer blocked)
  • Once complete, if the Javascript made changes to the DOM, this forces the construction of a new render tree.
  • This builds a layout, which the browser then renders or paints to the screen

You read that correct, the browser blocks when downloading Javascript files. This can be a real deal breaker for users and can cause a progressively loading page to stop dead in it's tracks. This blocking is a result of the potential use of document.write which can write HTML or Javascript to the document. This means the user has to wait patiently for the Javascript to download, parse, and run before any progress can be made with the page rendering. To avoid this type of client latency, you want to Put Scripts at the Bottom or use async or defer script tags.

All sub-resources have been downloaded, the page has been rendered, and now the user gets to actually do something. As the user navigates around your web application, Javascript is executing as your user triggers state changing events.

Inefficient or slow executing Javascript has the effect of reducing the browsers render/paint rate. This can cause "jank" which is defined as "problematic blocking of a software application's user interface due to slow operations." Without going into great detail, it's important to note that this type of latency is highly noticable to the user. Understanding how to properly use your developer tools is key in the battle against jank. Visit jankfree.org for more information.

Javascript that heavily manipulates the DOM is prone to reduced performance and increased client latency due to the triggering of excessive reflows. Excessive reflows will make the user's browser stutter, which is quite noticable. Everytime you change the DOM, this triggers reflows which forces the construction of a new render tree and then a re-paint of the screen. The DOM is slow, so it's best to take a batch approach when dealing with the DOM. This means, do all your DOM reads first and then do all your DOM writes second (and minimizing the amount of DOM writes).

// Bad!
var height = $('.container').height();
$('.container').height(height + 100);
var width = $('.container').width();
$('.container').width(width + 100);

// Good!
var height = $('.container').height();
var width = $('.container').width();
$('.container').height(height + 100);
$('.container').width(width + 100);

Finally, client latency can also appear when you make a XMLHttpRequest in Javascript. The user has to yet again wait on the network, however clever UX tricks (i.e. loading & transition animations) can help make this feel less noticeable to the user.

Conclusion
At the end of the day, the performance of your web application directly affects the user experience. Latency is a given in any networking application, so understanding how to mitigate its effects on your application will help improve performance and your overall user experience.

More Stories By Dan Riti

Dan Riti is a software developer with AppNeta with a passion for Python, JavaScript and music with a lot of bass.

@ThingsExpo Stories
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
BnkToTheFuture.com is the largest online investment platform for investing in FinTech, Bitcoin and Blockchain companies. We believe the future of finance looks very different from the past and we aim to invest and provide trading opportunities for qualifying investors that want to build a portfolio in the sector in compliance with international financial regulations.
Imagine if you will, a retail floor so densely packed with sensors that they can pick up the movements of insects scurrying across a store aisle. Or a component of a piece of factory equipment so well-instrumented that its digital twin provides resolution down to the micrometer.
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settle...
Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
"IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
When shopping for a new data processing platform for IoT solutions, many development teams want to be able to test-drive options before making a choice. Yet when evaluating an IoT solution, it’s simply not feasible to do so at scale with physical devices. Building a sensor simulator is the next best choice; however, generating a realistic simulation at very high TPS with ease of configurability is a formidable challenge. When dealing with multiple application or transport protocols, you would be...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
We are given a desktop platform with Java 8 or Java 9 installed and seek to find a way to deploy high-performance Java applications that use Java 3D and/or Jogl without having to run an installer. We are subject to the constraint that the applications be signed and deployed so that they can be run in a trusted environment (i.e., outside of the sandbox). Further, we seek to do this in a way that does not depend on bundling a JRE with our applications, as this makes downloads and installations rat...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
Digital Transformation (DX) is not a "one-size-fits all" strategy. Each organization needs to develop its own unique, long-term DX plan. It must do so by realizing that we now live in a data-driven age, and that technologies such as Cloud Computing, Big Data, the IoT, Cognitive Computing, and Blockchain are only tools. In her general session at 21st Cloud Expo, Rebecca Wanta explained how the strategy must focus on DX and include a commitment from top management to create great IT jobs, monitor ...
"Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
The IoT Will Grow: In what might be the most obvious prediction of the decade, the IoT will continue to expand next year, with more and more devices coming online every single day. What isn’t so obvious about this prediction: where that growth will occur. The retail, healthcare, and industrial/supply chain industries will likely see the greatest growth. Forrester Research has predicted the IoT will become “the backbone” of customer value as it continues to grow. It is no surprise that retail is ...