Abusing JavaScript to Measure Web Performance

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While building boomerang, we developed many interesting methods to measure network performance characteristics using JavaScript running in the browser. While the W3C's NavigationTiming API provides access to many performance metrics, there's far more you can get at with some creative tweaking and analysis of how the browser reacts to certain requests.

In this talk, I'll go into the details of how boomerang works to measure network throughput, latency, TCP connect time, DNS time and IPv6 connectivity. I'll also touch upon some of the other performance related browser APIs we use to gather useful information. I will NOT be covering the W3C Navigation Timing API since that's been covered by Alois Reitbauer in a previous Boston Web Perf talk.

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Abusing JavaScript to Measure Web Performance

  1. 1. • Philip Tellis• .com• philip@lognormal.com• @bluesmoon• geek paranoid speedfreak• http://bluesmoon.info/ Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 1
  2. 2. I <3 JavaScriptBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 2
  3. 3. So much that I wore Mustache socks to my wedding Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 3
  4. 4. I’m also a Web SpeedfreakBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 4
  5. 5. We measure real user website performanceBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 5
  6. 6. This talk is (mostly) about how we abuse JavaScript to do it Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 6
  7. 7. Abusing JavaScript to Measure Web Performance Philip Tellis / philip@lognormal.com Boston #WebPerf Meetup / 2012-07-24Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 7
  8. 8. First, a note about the code Note that in the code that follows, + new Date is equivalent to new Date().getTime() Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 8
  9. 9. 1 LatencyBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 9
  10. 10. 1 Blinking Lights It takes about 16ms for light to get from SF to Boston (24ms through fibre) ... Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 10
  11. 11. 1 Blinking Lights It takes about 16ms for light to get from SF to Boston (24ms through fibre) Though it takes about 100ms to ping... why? Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 10
  12. 12. 1 HTTP Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 11
  13. 13. So to measure latency, we need to send 1 packet each way, and time it Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 12
  14. 14. 1 Network latency in JavaScript var ts, rtt, img = new Image; img.onload=function() { rtt=(+new Date - ts) }; ts = +new Date; img.src="/1x1.gif"; Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 13
  15. 15. 1 Notes • 1x1 gif is 35 bytes • including HTTP headers, is smaller than a TCP packet • Fires onload on all browsers • 0 byte image fires onerror • which is indistinguishable from network error Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 14
  16. 16. 2 TCP handshakeBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 15
  17. 17. 2 ACK-ACK-ACK Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 16
  18. 18. 2 Connection: keep-alive Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 17
  19. 19. 2 Network latency & TCP handshake in JavaScript var t=[], tcp, rtt; var ld = function() { t.push(+new Date); if(t.length > 2) // run 2 times done(); else { var img = new Image; img.onload = ld; img.src="/1x1.gif?" + Math.random() + ’=’ + new Date; } }; var done = function() { rtt=t[2]-t[1]; tcp=t[1]-t[0]-rtt; }; ld(); Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 18
  20. 20. Notice that we’ve ignored DNS lookup time here... how would you measure it? Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 19
  21. 21. Network Throughput 3Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 20
  22. 22. 3 Measuring Network Throughput data_length download_time Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 21
  23. 23. Should you fly a 747 or a 737? • A 747 seats 400+ passengers • A 737 seats about 150 • Both take about the same time to fly from SFO to BOS • A 747 takes longer to load and unload The best selling aircraft to date is the 737 Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 22
  24. 24. 3 Network Throughput in JavaScript // Assume global object // image={ url: ..., size: ... } var ts, rtt, bw, img = new Image; img.onload=function() { rtt=(+new Date - ts); bw = image.size*1000/rtt; // rtt is in ms }; ts = +new Date; img.src=image.url; Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 23
  25. 25. 3 Measuring Network Throughput If it were that simple, I wouldn’t be doing this talk. Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 24
  26. 26. 3 TCP Slow Start Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 25
  27. 27. 3 Measuring Network Throughput So to make the best use of bandwidth, we need resources that fit in a TCP window Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 26
  28. 28. 3 There is no single size that will tax all available networks http://www.yuiblog.com/blog/2010/04/08/analyzing-bandwidth-and-latency/ Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 27
  29. 29. 3 Network Throughput in JavaScript – Take 2 // image object is now an array of multiple images var i=0; var ld = function() { if(i>0) image[i-1].end = +new Date; if(i >= image.length) done(); else { var img = new Image; img.onload = ld; image[i].start = +new Date; img.src=image[i].url; } i++; }; Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 28
  30. 30. 3 Measuring Network Throughput Slow network connection, meet really huge image Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 29
  31. 31. 3 Network Throughput in JavaScript – Take 3 var img = new Image; img.onload = ld; image[i].start = +new Date; image[i].timer = setTimeout(function() { image[i].expired=true }, image[i].timeout); img.src=image[i].url; Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 30
  32. 32. 3 Network Throughput in JavaScript – Take 3 if(i>0) { image[i-1].end = +new Date; clearTimeout(image[i-1].timer); } Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 31
  33. 33. 3 Network Throughput in JavaScript – Take 3 if(i >= image.length || (i > 0 && image[i-1].expired)) { done(); } Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 32
  34. 34. 3 Measuring Network Throughput Are we done yet? Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 33
  35. 35. 3 Measuring Network Throughput Are we done yet? sure... Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 33
  36. 36. 3 Measuring Network Throughput Except network throughput is different every time you test it Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 34
  37. 37. Statistics to the Rescueflickr/sophistechate/4264466015/ Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 35
  38. 38. 3 Measuring Network Throughput The code for that is NOT gonna fit on a slide Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 36
  39. 39. But this is sort of what we see world-wide Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 37
  40. 40. And it’s different for different countries This is India Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 38
  41. 41. 4 DNSBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 39
  42. 42. 4 Measuring DNS time_with_dns − time_without_dns Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 40
  43. 43. 4 Measuring DNS in JavaScript var t=[], dns, ip, hosts=[’http://hostname.com/’, ’http://ip.ad.dr.ess/’]; var ld = function() { t.push(+new Date); if(t.length > hosts.length) done(); else { var img = new Image; img.onload = ld; img.src=hosts[t.length-1] + "/1x1.gif"; } }; var done = function() { ip=t[2]-t[1]; dns=t[1]-t[0]-ip; }; ld(); Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 41
  44. 44. 4 Measuring DNS • What if the IP changes? • What if DNS is cached? • What if you map DNS based on geo location? Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 42
  45. 45. 4 Wildcard DNS Entries *.foo.com → IP address Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 43
  46. 46. 4 Measuring DNS in JavaScript – take 2 var base_url="http://*.foo.com/", timers = {}, gen_url=""; function start() { var random = Math.random().toString(36), cache_bust = Math.random(), img = new Image(); gen_url = base_url.replace(/*/, random); img.onload = A_loaded; timers.start = +new Date; img.src = gen_url + "image-l.gif?t=" + cache_bust; } Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 44
  47. 47. 4 Measuring DNS in JavaScript – take 2 function A_loaded() { var cache_bust = Math.random(), img = new Image(); img.onload = B_loaded; timers.a_loaded = +new Date; img.src = gen_url + "image-l.gif?t=" + cache_bust; } I’ll let you figure out B_loaded Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 45
  48. 48. 4 Measuring DNS Full code in boomerang’s DNS plugin Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 46
  49. 49. 5 IPv6Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 47
  50. 50. 5 Measuring IPv6 support and latency 1 Try to load image from IPv6 host • If timeout or error, then no IPv6 support • If successful, then calculate latency and proceed 2 Try to load image from hostname that resolves only to IPv6 host • If timeout or error, then DNS server doesn’t support IPv6 • If successful, calculate latency Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 48
  51. 51. 5 Measuring IPv6 support and latency Full code in boomerang’s IPv6 plugin Note, only run this if you know IPv6 is supported by the client Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 49
  52. 52. 6 Other StuffBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 50
  53. 53. 6 Other Stuff We Measure • NavTiming – navtiming.js • navigation.connection.type – mobile.js • window.performance.memory – memory.js • Number of DOM nodes and byte size of HTML – memory.js Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 51
  54. 54. And we try to do it fastBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 52
  55. 55. – .done()Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 53
  56. 56. Code/References • http://lognormal.github.com/boomerang/doc/ (BSD Licensed) • www.lognormal.com Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 54
  57. 57. • Philip Tellis• .com• philip@lognormal.com• @bluesmoon• geek paranoid speedfreak• http://bluesmoon.info/ Boston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 55
  58. 58. Thank you Ask me about a discount codeBoston #WebPerf Meetup / 2012-07-24 Abusing JavaScript to Measure Web Performance 56
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