Measuring Front-End Performance - What, When and How?
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This document discusses front-end performance measurement. It recommends measuring performance at every stage of a project's lifecycle using both synthetic and real user monitoring tools. Key metrics to measure include time to first byte, speed index, user timings. Both types of tools provide valuable but different insights and should be used together. Performance data should be reported visually through dashboards to make it relevant and actionable. The goal is to establish a "culture of performance" and catch problems early.
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Measuring Front-End Performance - What, When and How?
- 1. Gareth Hughes, @brassic_lint Measuring Front-end Performance: What, When and How? Gareth Hughes, @brassic_lint
- 2. What?
- 3. –Akamai study, 2009 http://uk.akamai.com/html/about/press/releases/2009/press_091409.html “47% of consumers expect a web page to load in 2 seconds or less”
- 4. –Akamai study, 2009 “47% of consumers expect a web page to load in 2 seconds or less”
- 5. Anatomy of an HTTP request TTFB (Time to First Byte)
- 6. Time to glass Render Tree HTML CSS DOM CSSOM Layout Paint DOM Content Loaded Render Start JavaScript DOM CSSOM
- 9. In the browser function myTimings() { performance.mark("startTask1"); doTask1(); // Some developer code performance.mark("endTask1"); performance.mark("startTask2"); doTask2(); // Some developer code performance.mark("endTask2"); } http://www.w3.org/TR/user-timing/
- 10. Speed Index
- 11. What?
- 12. • Response End / TTFB How quickly has my server served the base page • DOM Content Loaded A good analogy for “Page is usable” • Render Start / First Paint Gives us an indication of when the user actually sees something • Total Page Load Although this includes all 3rd-party and deferred content, it can help get a “feel” for how well everything is working • User Timings This is a little more work, but allows the ability to instrument the areas important to you • Speed Index This is a great single metric to give a pretty good idea of overall user experience What?
- 13. When?
- 15. –Brad Frost http://bradfrost.com/blog/post/performance-as-design/ “Good performance is good design”
- 16. Performance Budgets • Defines tangible numbers or metrics • May be defined by an aspiration or industry standards • Enforces the performance standards • Instills a “culture of performance” in the project team • Gives a mark to measure by • You probably already have one! • Start vague, but define early • “Performance is everyone’s problem”
- 17. When? At every stage of the lifecycle!
- 18. How?
- 19. Synthetic Domo arigato, Mr. Roboto
- 21. http://www.webpagetest.org • Free! • Real browsers • Global • Scripting • API • Mobile devices • OSS
- 24. • sitespeed.io Uses WPT & PhantomJS to run performance audits on site. • Can be used internally (CLI tool) • PerfBar (http://wpotools.github.io/perfBar/) Surfaces NavTiming data in the browser • Useful on UAT-type environments • CI plugins • Test for performance as part of the CI process Other Tools
- 25. Reporting Data
- 27. Custom Dashboards Graphite / Splunk
- 28. How? • Synthetic External, controlled testing • Real User Monitoring Browser-based reporting of real user’s experience • Don’t choose! Both synthetic and RUM provide valuable insight into performance and should be seen as complementary - either alone gives a narrow view • Report Display data on dashboards, make it visible and relevant
- 29. Summary • What: Decide what metrics are relevant to User Experience • When: At every stage of the lifecycle • How: Using tools and reports to make the data relevant and actionable
- 30. –Ian Malpass, Etsy, https://codeascraft.com/2011/02/15/measure-anything-measure-everything/ “If it moves, we track it. Sometimes we’ll draw a graph of something that isn’t moving yet, just in case it decides to make a run for it.”
- 31. Gareth Hughes, @brassic_lint Thank you! http://www.slideshare.net/GarethHughes3 Gareth Hughes, @brassic_lint
Editor's Notes
- Start with the what…? What shall we measure? more questions: meaningful? how our pages are performing? user experience?
- what do users *mean*? The page is usable? All objects are loaded?
- When the browser wheel stops spinning? Can’t answer Can help to find out Know what you can measure to ensure you are meeting you user’s expectations.
- Let’s start with the basics… request an object over HTTP basic steps to deliver an object over HTTP, measure all of these indication of the page delivery performance bundle the back-end metrics into TTFB
- HTML page has been downloaded how the rest of the page gets built and displayed DOM = document object model very simplistic model partial render tree render start may happen before DCL elephant in the room: JavaScript! blocks DOM construction CSSOM construction blocks JavaScript execution! maybe DCL is a useful metric…?
- Once in the browser, there are APIs we can use to collect these, and other metrics… The NavTiming API… Lots of metrics covering navigation, page load + browser events like DCL http://www.w3.org/TR/navigation-timing/
- The ResourceTiming API… Performance metrics for page objects / resources NB Subject to CORS Must have an allow header (Timing-Allow-Origin)
- ultimate flexibility, the UserTimings API own timing marks in JS Guardian 1st party JS app instrumented
- Measure of how quickly the visible portions are drawn Visual completeness during page load Index of how long spent Incomplete Example: Start and End at the same time Graphing completeness over time gives… Can see that A is more complete more quickly B is Incomplete longer = worse UX Index calc’d from area above Larger area = larger index = worse UX More detail on formula online Used in synthetic Can be calc’d from browser paint events unreliable & not used commercially
- So let’s return to the “What?”… Huge number of metrics What can we use to represent UX? Depends a starting point of what I use…
- Response End How quickly has my server served the base page DOM Content Loaded A good analogy for “Page is usable” Render Start / First Paint Gives us an indication of when the user actually sees something Total Page Load Although this includes all 3rd-party and deferred content, it can help get a “feel” for how well everything is working User Timings This is a little more work, but allows the ability to instrument the areas important to you Speed Index This is a great single metric to give a pretty good idea of overall user experience
- let’s look at the “When?” when to test develop then test and hope?
- Example of a waterfall methodology when to measure performance? without saying do it in test and probably development. What about requirements? Performance should be a NFR And monitoring performance after release editors add content, marketing add tags ensure that users are still getting the optimal experience. what about during Design…?
- Brad Frost tells us… Good performance is good design Many articles on designing for performance book on it by Lara Hogan. Designing to be fast from the beginning, rather than trying to optimise, will always give a better experience for end-users, saves time in development & test, and makes the life of a developer a heck of a lot easier!
- A key way to achieve this is to set Performance Budgets; dev & design collaborating on designing a fast site PERFORMANCE IS EVERYONE’S PROBLEM
- So… we come back to the question of When? At every stage of the lifecycle But how do we do that?
- We know: what to measure, when to measure. But how? I’ll walk you through some of the options, using examples of tools on the way.
- Synthetic, often referred to as “robots”. many forms simple curl-type requests measuring the HTTP req also commonly used for availability monitoring doesn’t tell us a lot about UX easy, and often free or very cheap.
- Better to test using “real” browsers - emulated browser to load the page at regularly - external (generally) Methodologies vary Test under (relatively) consistent conditions. Emulated browsers for control Graph-based portals waterfall charts Also test from real VMs running desktop (or mobile in some cases) browsers. Some will use these for regular testing, as well as for single tests. Also screenshots filmstrips videos Key is consistency - Stable - Bandwidth - Latency Can’t compare otherwise
- Webpagetest is a fantastic resource it’s free, test from real browsers all over the world. Can build scripts to do things like authentication, click-paths. API to run tests, and get results, plenty of tools use this to automate measurement build pipelines - other reporting suites (sitespeed.io) Real mobile devices (Android and iOS) - US based. Open source, available on github… own private instance on your own network, A few minutes on AWS (pre-built AMIs). Great tool for testing before production as you can put it anywhere you need!
- How our site is really performing for end users, we need to get metrics from them. We know browsers provide a mechanism for getting data how do we get the millions(?) of data points and make sense of them? Start on the rum… no,“Real User Monitoring” Typically, small JS tag collect the metrics and beacon to a portal Some analytics will also collect basic performance data Like GA, Usually very basic and heavily sampled
- But how do we make sense of all this data? Eternal question for RUM data. Portals allow you to analyse the avalanche of data Often averages, percentiles or aggregations Valuable, but takes work Allows visibility into UX Further investigation before conclusions can be drawn Poor performance in Mexico could be poor CDN performance in the region A local connectivity issue Even, a single data point from a user on dial-up ;) HISTOGRAMS
- Other Tools Sitespeed - CLI - PhantomJS - WPT runner - internal Perfbar in UAT or for internal users CI plugins - fail the build on broken budgets
- So what are we going to do with all this data we’re collecting? Use to optimise the site Find areas to improve, RUM data might show situational optimisations But what else can we do with it?
- Speedcurve offers a number of high-level visualisations. Example here shows number of images on homepage Marked performance budget Markers to show deployments. Can be used to “publicise” site performance I know teams that display around the offices Make sure everyone knows what’s going on. “performance is everyones problem”.
- API access to the data, Build custom dashboards Graphite (with Grafana as a front-end) on the left, and Splunk on the right. Flexibility to integrate performance data business needs, other data sources like analytics, combining synthetic and RUM data, Build your own story Display data in a way that’s meaningful to everyone.
- So How…
- I’ll leave you with this quote from a 2011 blog entry from Ian Malpass at Etsy… this is their philosophy. However it’s important to remember to focus on what’s important to you, while collecting all the data you possibly can - you never know when it may be useful! https://codeascraft.com/2011/02/15/measure-anything-measure-everything/