Are Today’s Good Practices… Tomorrow’s Performance Anti-Patterns?

Independent Web Performance Consultant at Asteno
Nov. 15, 2013

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Are Today’s Good Practices… Tomorrow’s Performance Anti-Patterns?

  1. Are Today’s Good Practices… Tomorrow’s Performance Anti-Patterns? @andydavies #VelocityConf, London
  2. What if … … dataURIs are an anti-pattern?
  4. dataURIs for CSS images Makes a blocking resource larger by including non-blocking resources • Browser can’t start rendering page until CSS has downloaded * • Images don’t block Do they have the same caching lifetime? * Some browsers defer download of CSS when media query doesn’t match
  5. Test the theory
  6. 1. Take 50 icons 2. Create 50 stylesheets, each with one more dataURI than previous 3. Create matching HTML file for each stylesheet 4. Test them all!
  7. Larger CSS download = longer time to RenderStart RenderStart - TTFB (ms) 1000 875 750 625 500 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 Number of Sprites
  8. This got me thinking!
  9. We have our rules…
  10. and we love recipes…
  11. But, what happens when things change?
  12. Browsers already use the network differently
  13. New network protocols are coming here
  14. Differences in TCP Connection Use HTTP 1.1 SPDY
  15. New Standards - opportunities and challenges
  16. How much do we rely on inline JavaScript?
  17. 73% of visitors support async attribute <script async src="myscript.js"><script>
  18. Yet, this is how we typically asynchronously load scripts <script type="text/javascript"> function() { var js = document.createElement('script'); js.async = true; js.src = 'myscript.js'; var e = document.getElementsByTagName('script')[0]; e.parentNode.insertBefore(js, first); })(); </script>
  19. XSS
  20. Content-Security-Policy “Content Security Policy, a mechanism web applications can use to mitigate a broad class of content injection vulnerabilities, such as cross-site scripting (XSS)”
  21. Example Only allow scripts to be executed if they come from a designated host, disables inline scripts by default. Content-Security-Policy: script-src Can re-enable inline scripts, but increases XSS risk Content-Security-Policy script-src 'self'
  22. What other performance enhancements do we rely on inline JS for? Guardian split page into - Content - Enhancements - Leftovers Others rely on scroll handlers for lazyloading
  23. Resource Priorities - adds lazyload and postpone attributes
  24. So what about the network?
  25. Tested some scenarios, measured the outcomes
  26. Test Environment - EC2 - Medium Instance - Dublin - Apache 2.2 - GZIP - Keep-Alive - mod_pagespeed - mod_spdy - WepPageTest, Dulles / Chrome / Cable
  27. Off the shelf website template
  28. Minimal Optimisations - HTTP 1.1 vs SPDY 0s 1s 2s 3s 4s HTTP SPDY SPDY is faster (GZIP / Keep-Alive / initcwnd 10) 5s 6s
  29. Waterfall for HTTP Test
  30. Waterfall for SPDY Test
  31. So which rules are most likely to be at risk? - Split dominant content domains - Reduce requests - Merging - Sprites - DataURIs
  32. Sharding CSS background: url() images 0s 1s 2s 3s 4s 5s Sharded Not Sharded Sharded page is much slower 6s 7s 8s
  33. Connection to shard opened later New TCP connection opened
  34. New connection shouldn’t have been opened “Both chrome and firefox will automatically unshard transparently for you when using spdy and both of the sharded hosts are at the same IP address and covered under one SSL cert (e.g. *” Patrick McManus, Mozilla
  35. Sharding <img src= 0s 1s 2s 3s 4s 5s 6s Sharded Not Sharded Sharded page is marginally faster??? 7s 8s
  36. Other tests carried out - Sharding JS / CSS Horrible - Merging CSS Slower - Server Push No noticable difference - jQuery from Google CDN Suprisingly quick
  37. Hmm… How do we move forward?
  38. It’s only going to get more complex “Situational Performance Optimization, The Next Frontier” Guy Podjarny
  39. Will complexity lead to the end of hand crafted optimisations?
  40. mod_pagespeed & mod_spdy == tools to experiment # Disable concatenation for SPDY/HTTP 2.0 clients <ModPagespeedIf spdy> ModPagespeedDisableFilters combine_css,combine_javascript </ModPagespeedIf> # Shard assets for HTTP 1.x clients only <ModPagespeedIf !spdy> ModPagespeedShardDomain, </ModPagespeedIf> High Performance Browser Networking, Ilya Grigorik
  41. Start experimenting, share your experiences
  42. We need to improve our toolkit
  43. SPDY waterfall in Firefox! We need to help fix things like this
  44. Limits to what new protocols or automation can fix Requests by Domain Bytes by Domain
  46. Thank You! @andydavies