Web performance is a complicated topic, but over the years it’s become easier to articulate thanks to incredible advancements in performance features, their adoption in the browser ecosystem and tools that test and give insight into which techniques might speed up your site. However, all too often a feature is implemented incorrectly, resulting in a lost opportunity for performance improvement. During this talk I’d like to explore a few common web performance techniques - some that you are likely already familiar with. We’ll dive into HTTP Archive data to find some examples of sites that are using them incorrectly, and explore the impact and potential benefits of fixing them. https://webdirections.org/lazyload/speakers/paul-calvano.php

1. Performance Mistakes
…an HTTP Archive Deep Dive
Performance Architect @Etsy
Paul Calvano
@paulcalvano

2. https://httparchive.org

3. 3
How the HTTP Archive Works
● httparchive.org
○ Monthly trends
○ Discussion forum
○ Web Almanac
Chrome UX Report
~8.5 million URLs

4. https://almanac.httparchive.org/
4

5. <img src="example.jpg" loading="lazy" />
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https://web.dev/lazy-loading-images/

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https://caniuse.com/loading-lazy-attr

7. Source: https://almanac.httparchive.org/en/2021/media#lazy-loading

8. 8
https://web.dev/lcp-lazy-loading/

9. 9
https://almanac.httparchive.org/en/2021/performance#fig-20

10. 10
https://web.dev/lcp-lazy-loading/

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Source: HTTP Archive, April 2022 - Mobile
315,940
Sites failed the
Lazy Loaded LCP audit
Examples
https://www.flipkart.com/
https://open.spotify.com/
https://ml.t-mobile.com/en/home
https://store.playstation.com/
https://www.nba.com/

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https://almanac.httparchive.org/en/2021/resource-hints

13. 13
https://almanac.httparchive.org/en/2021/resource-hints

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dns–prefetch is used more often than preconnect.
If you are using dns-prefetch and the domain is used to load content on the same page,
use preconnect instead!

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<link rel="preconnect" href="//i.etsystatic.com" />
Why does this look like a dns-prefetch instead of a preconnect?

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https://w3c.github.io/resource-hints/

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Source: HTTP Archive, April 2022
9.7 Million
Preconnect Headers
4.5 Million
Preconnects in HTML
101K
Missing crossorigin
2.8 Million
Missing crossorigin
These work fine.
¯_(ツ)_/¯
Many are blocked by CORS

18. Examples
https://www.etsy.com/
https://www.ikea.com/
https://nypost.com/
https://www.chess.com/
https://www.tiktok.com/
https://www.dell.com/
https://www.realtor.com/
18

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https://web.dev/preload-critical-assets/
<link rel="preload" as="font" href="/assets/Pacifo-Bold.woff2">

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430K
Sites’ with Unused Preloads
Examples
https://www.washingtonpost.com/
https://www.amazon.com/
https://www.redfin.com/
https://www.wayfair.com/
https://tinder.com/
https://weather.com/
https://www.dailymail.co.uk/

21. 21
318
Unused Preloads

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https://almanac.httparchive.org/en/2021/compression

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https://almanac.httparchive.org/en/2021/compression

24. 24
https://almanac.httparchive.org/en/2021/compression

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http://nginx.org/en/docs/http/ngx_http_gzip_module.html
NGINX’s default gzip compression level is 1
If you use NGINX, check your compression levels.
If you make a change to your compression levels, you will also need to purge CDN
caches, because they cache the compressed content you served.

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https://tools.paulcalvano.com/compression.php
/smart/buttons Test Expected % Diff
Uncompressed 373 KB 373 KB -
Gzip Compressed 130 KB 99 KB 31% larger
Brotli Compressed 152 KB 113 KB 35% larger

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https://tools.paulcalvano.com/compression.php

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226K
Sites’ with >5 first party
Images served compressed
Examples
https://www.costcotravel.com
https://www.cricketwireless.com
https://www.ryanair.com
https://www.basspro.com
https://support.apple.com

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● Lazy Loading
○ Don’t lazy load above-the-fold images
○ Check Lighthouse audit for lazy loading LCP image
● Resource Hints
○ If using dns-prefetch for domains loaded on the same page, use preconnect
instead.
○ Are your Preconnects are actually being used? Check the crossorigin attributes
○ Check the console to ensure you don’t have unused preloads
● Compression
○ Using NGINX? Check your gzip compression levels
○ Test your largest resource - are compression levels within expected ranges?
○ Avoid compressing binary responses such as images.

30. HTTP Archive Web Almanac

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Thanks!
bit.ly/ha-slack
Chat
github.com/HTTPArchive
Contribute
discuss.httparchive.org
Collaborate
@paulcalvano
paul@httparchive.org